Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Modifications in curved pi-electronic systems, dipyrrolylbenzodiazepines, resulted in various derivatives with modulated electronic properties and assembly behaviour. The electron-rich pyrrole-based curved pi-system exhibited C-60 complexation in the form of a hydrogen-bonding cyclic hexamer, giving rise to solid-state photo-induced electron transfer as elucidated by transient absorption spectroscopy.

DOI： 10.1039/d2cp01575g

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DOI： 10.1021/acs.jpcc.1c09163

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DOI： 10.1021/acs.jpcc.1c06785

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

In this study, charged pi-electronic species are observed to develop stacking structures based on electrostatic and dispersion forces. (i)pi-(i)pi Interaction, defined herein, functions for the stacking structures consisting of charged pi-electronic species and is in contrast to conventional pi-pi interaction, which mainly exhibits dispersion force, for electronically neutral pi-electronic species. Establishing the concept of (i)pi-(i)pi interaction requires the evaluation of interionic interactions for pi-electronic ion pairs. Free base (metal-free) and diamagnetic metal complexes of 5-hydroxy-10,15,20-tris(pentafluorophenyl)porphyrin were synthesized, producing pi-electronic anions upon the deprotonation of the hydroxy unit. Coexisting cations in the ion pairs with porphyrin anions were introduced as the counter species of the hydroxy anion as a base for commercially available cations and as ion-exchanged species, via Na+ in the intermediate ion pairs, for synthesized pi-electronic cations. Solid-state ion-pairing assemblies were constructed for the porphyrin anions in combination with aliphatic tetrabutylammonium (TBA(+)) and pi-electronic 4,8,12-tripropyl-4,8,12-triazatriangulenium (TATA(+)) cations. The ordered arrangements of charged species, with the contributions of the charge-by-charge and charge-segregated modes, were observed according to the constituent charged building units. The energy decomposition analysis (EDA) of single-crystal packing structures revealed that electrostatic and dispersion forces are important factors in stabilizing the stacking of pi-electronic ions. Furthermore, crystal-state absorption spectra of the ion pairs were correlated with the assembling modes. Transient absorption spectroscopy of the single crystals revealed the occurrence of photoinduced electron transfer from the pi-electronic anion in the charge-segregated mode.

DOI： 10.1039/d1sc02260a

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>We demonstrated molecular detection using aptamer-modified gold nanoparticles with DNA-brush for the prevention of non-specific aggregation and smartphone darkfield microscopy.</p>

DOI： 10.1039/d0ra05149g

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© The Royal Society of Chemistry. Intense ns pulse laser excitation to nanoparticle colloids of a photochromic diarylethene induced an amplified cycloreversion reaction. The mechanism was explained as a 'photosynergetic response' coupled with nanoscale laser heating and the photochemical reaction in nanoparticles.

DOI： 10.1039/d0cc00884b

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Laser Institute of America  

Chloroaluminum phthalocyanine nanoparticles were successfully prepared by laser ablation in liquid, and the photoacoustic signal of the nanoparticles was measured. Chloroaluminum phthalocyanine powders were irradiated with nanosecond-pulsed laser (Nd:YAG, SHG) to prepare nanoparticles. The particle size of prepared nanoparticles decreased with the increase in laser fluence. Absorbance of prepared nanoparticles was increased with the increase in laser fluence. The ratio between two peaks would be changed because of crystal structure change by photothermal laser heating. The production yield from raw material powder to nanoparticle was 92.8% at a laser fluence of 300 mJ/cm2. The nanoparticle-dispersed solution was stable for 80 days. The photoacoustic signal intensity of prepared nanoparticles increased with the increase in laser fluence.

DOI： 10.2351/7.0000101

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© 2020 The Chemical Society of Japan. Magnetic α-Fe2O3/Fe3O4 composite spherical particles were synthesized by nanosecond pulsed laser irradiation to α-Fe2O3 nanoparticle powder suspended in pure water and acetone. It was shown that the laser-induced reduction efficiencies in two solvents were comparable. The obtained submicrometer spheres exhibited a ferromagnetic property having a higher coercivity than that of commercial Fe3O4

DOI： 10.1246/cl.190947

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A novel femtosecond pump-probe microspectroscope using a femtosecond Ti:Sapphire oscillator as a light source was developed. The fundamental specifications are the temporal resolution of 350 fs, the spatial resolution of 770 nm, and the tunable probe wavelength in the region from 500 to 900 nm. The setup has two modes of the probe light detection; one is back-scattered light detection and another conventional transmitted light detection. The back-scattering mode measurement demonstrated about 20-times higher gain of the transient signal of single nanoparticles compared to the conventional transmittance-mode one. This high-sensitivity enables the single nanoparticle ultrafast spectroscopy of organic nanomaterials which in general are low photo-durability. The femtosecond pumpprobe microspectroscopy is fruitful in the researches of solid-state photochemical processes characterized by restricted molecular motions and intermolecular electronic interactions in the confined space. The potential applications of the developed microspectroscopic system are demonstrated for the picosecond excited state dynamics of nm- to μm-sized organic crystals.

DOI： 10.1007/978-981-15-5451-3_29

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DOI： 10.1016/j.apsusc.2019.01.221

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DOI： 10.2116/analsci.18P571

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Gold nanoparticles (AuNPs) have been commonly used in molecular sensing, in the form of observation of the color change from red to blue of the AuNP solution, caused by target-molecule-induced AuNP aggregation. In this work, the changes in absorbance and scattering spectra caused by AuNP aggregation were studied using thrombin-induced AuNP aggregation as a model. We demonstrated for the first time that scattering spectra is more sensitive to the changes owing to AuNP aggregation than absorbance spectra. Moreover, a digital color analysis of darkfield images using dark field microscopy (DFM) facilitated a simple method for detection of AuNPs aggregation without the use of spectroscopic analysis. Furthermore, we demonstrated that DFM is useful for detecting AuNPs aggregation in a colored solution, in which the color change by AuNPs aggregation is not visible.

DOI： 10.2116/analsci.18P571

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DOI： 10.1021/acs.jpcc.9b01044

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DOI： 10.1021/acs.jpcc.9b01391

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© 2019 The Ceramic Society of Japan. All rights reserved. Calcium phosphates are essential compounds for the sustenance of life, since, for example, many grains that enable to convert food are necessary for use of the fertilizers made of chemically synthesized crystals. We have demonstrated two alternative dry processes for the conversion of hydroxyapatite to tricalcium phosphate by means of thermodynamically controlled heat and electronically generated heat with pulsed laser light. In addition, the conversion efficiency has been quantitatively determined from the Rietveld analysis for powder X-ray diffractionpatterns of the fired and laser-ablated samples. Both conversion processes recycled animals' bones as the source of calcium phosphate, and in the future, this could compensate for the niche area in the absence of wet process for a phosphorus containing sludge through a sewage treatment.

DOI： 10.2109/jcersj2.18190

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© 2019 The Japan Society of Applied Physics. One- and two-photon absorption coefficients in Bi2O3-B2O3 and Bi2O3-SiO2 glasses, which are characterized with zero photoelasticity and visible transparency, are studied. The two systems show a similar compositional dependence in photoelastic constant (PEC), which can be accounted for by electronic structure of Bi3+. The one-photon absorption coefficients in borate and silicate glasses depend on the existence of charge transfer phenomena, while the two-photon absorption coefficients obtained by Z-scan measurement is independent of the one-photon absorption. The interpretation by optical transition probabilities can be extended to elucidate the optical nonlinearity in ns2-type cation containing oxide glasses with zero PEC.

DOI： 10.7567/1882-0786/ab40f4

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© 2018 Wiley-VCH Verlag GmbH &amp; Co. KGaA, Weinheim. Iron-based nanoparticles (FeNPs) have unique and attractive properties such as superparamagnetism, biocompatibility, and catalytic activity. Although the synthesis of precious metal NPs from a metal in liquid and/or metal salt solution by a pulsed laser has been investigated, comparably little effort has been devoted to examine the production of FeNPs. Here we report the synthesis of carbon-shell free spherical NPs of iron oxide (magnetite) from ferrocene hexane solution by femtosecond near infrared laser pulses. Nanosecond UV laser pulses are used to compare the evolution of the particle size distribution as a function of laser irradiation time. The size of NPs remains constant even for extended exposure to femtosecond laser pulses, whereas it grows with exposure to nanosecond laser pulses. The primary particles are generated by photochemical reactions regardless of pulse duration; however, the fragmentation of NPs by successive femtosecond laser pulses regulates the particle size.

DOI： 10.1002/cphc.201800436

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：FUJI TECHNOLOGY PRESS LTD  

Sedimentation in hydropower reservoirs is one of the most important problems facing power generation. Many of the reservoirs our company's dams, built in the postwar reconstruction period, have been storing up sedimentation for decades. The percentage of sedimentation is now considerable, about 9%, because of a combination of a high degree of sediment production and the river flow regime. We have been trying to excavate the sedimentation from the reservoirs to avoid aggradations of upstream riverbeds and to eliminate obstacles to intake and outlet functions. Considering sediment properties, we have carried out representative five different ways of managing reservoir sediment. At the Sakuma dam, which is comparatively large, provisional transporting inside the reservoir is the main countermeasure, but radical management will be required in the near future. At the Futatsuno dam and Taki dam, which are medium-sized, the current volume of sedimentation excavation is not sufficient to maintain the size of the reservoir, due to flow sedimentation. Sediment routing methods, such as bypassing, will therefore be urgently planned. At the Setoishi and Yambara dams, the testing of sediment sluicing or hydro-suction sediment removal systems has already started. Regarding sedimentation sluicing, we have studied the feasibility of sediment bypass tunnels and gated outlets in the dam reservoir that is unsuitable for sluicing with the existing spillway. We found that gated outlet will be effective. Although there are no quick remedies that can reduce reservoir sedimentation dramatically, there are some methods that may be suitable, considering the size, life and basin of each reservoir. Not only the technical feasibility, but also the economic advantages and ecological acceptability should be considered. To sustain reservoirs and hydropower, sedimentation should be managed effectively and adaptively, based on the specific conditions of each reservoir.

DOI： 10.20965/jdr.2018.p0702

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The excited-state dynamics of pyrene incorporated into poly(substituted methylene)s is investigated by picosecond time-resolved fluorescence spectroscopy and femtosecond time-resolved near-IR absorption spectroscopy in the 900-1400 nm region. The pyrene rings in poly (substituted methylene)s are photoexcited to the monomer excited state immediately after UV irradiation, followed by prompt excimer formation with time constants of a few picoseconds to a few hundred picoseconds. The excimer formation in poly(substituted methylene)s proceeds with much shorter time constants than that in pyrene-incorporated polyacrylates, vinyl polymer counterparts with the same side-chain structures, indicating the presence of stronger electronic interaction between the pyrene rings in poly(substituted methylene)s. The effects of every methylene substitution hold when each pyrene ring is connected to the polymer backbone with a monomethylene linker, while the effects are observed only weakly when a tetramethylene linker is employed. The results demonstrate the effectiveness of every methylene substitution in the prompt excimer formation of pyrene connected to the polymer backbone either directly or with the monomethylene linker.

DOI： 10.1021/acs.macromol.8b01060

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

Naphthalocyanine nanoparticles were prepared by laser ablation in liquid using second-harmonics of nanosecond Nd:YAG laser as an excitation light sauce at various laser fluence, and the properties of naphthalocyanine nanoparticles, such as shape, size, zeta potential, chemical structure and optical absorption were examined. The scanning electron microscopy (SEM) and dynamic light scattering (DLS) measurements showed that the particle size of the nanoparticles could be controlled by the laser fluence. The IR spectra of the nanoparticles indicated the formation of carboxylate anion species at laser fluences above 100 mJ/cm2, which will result the zeta potential of the nanoparticles depending on the laser fluence. We also examined the potential application to contrast agents for photoacoustic, and confirmed that the naphthalocyanine nanoparticles generated a strong photoacoustic signal.

DOI： 10.7567/JJAP.57.035001

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DOI： 10.1016/j.jphotochemrev.2018.02.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Chemical Society of Japan  

We prepared aqueous nanoparticle colloids of benzothiadiazole doped with diarylethene derivatives, which showed ON/OFF fluorescence photoswitching with a giant modulation of the fluorescence intensity at low density of photocolored closedform isomer of the diarylethene. The fluorescence intensity decreased nonlinearly with the photoconversion of the isomer from open-form to closed-form. The fluorescence quenching behavior was unrelated to the concentration of composed diarylethene chromophore (535mol%) in the nanoparticles.

DOI： 10.1246/cl.170973

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© 2018 the Owner Societies. Femtosecond excited-state dynamics of fullerene-C60 nanoparticles (nC60) having a mean size of 50 nm dispersed in pure water was studied by means of femtosecond transient absorption spectroscopy. The intermolecular charge-transfer (CT) excited state in solid C60 was directly and firstly observed by femtosecond 350 nm and 420 nm excitations, and its intrinsic lifetime of 0.35 ps was found. The CT excited state relaxed to the locally excited S1 state and excimers or directly to the ground state through geminate charge recombination. We also examined the laser fluence dependence of the CT excited-state dynamics. At a high laser fluence, the mutual interactions between neighboring CT excited states were observed immediately after the excitation. The interaction disappeared through the charge recombination in the geminate CT pair or between the neighboring CT excited states with a lifetime of 0.45 ps. After that, the locally excited S1 state decayed with a few ps lifetime independent of the fluence. In this paper, the mechanism and dynamics of the intermolecular CT excited state generated by UV light excitation is discussed in detail.

DOI： 10.1039/c7cp06746a

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Language：English   Publishing type：Part of collection (book)   Publisher：Springer Japan  

In this chapter, hybrid nanomaterials based on diarylethene molecules and gold nanoparticles (GNPs) are described. The interest of diarylethene derivatives incorporated in nanosystems and coupled to GNPs is first introduced. Different strategies to prepare hybrid nanosystems are then described, pointing out designs presenting specific merits and flaws. The photochromism-plasmonic coupling is presented, considering both units of the hybrid nanosystem. On the one hand, the photochromic reaction of the diarylethene molecules greatly modifies the surface plasmon resonance (SPR) mainly due to a change of the local refractive index. On the other hand, the enhanced electromagnetic field at the surface of the GNPs induces an enhancement of the photochromic kinetics under visible light irradiation. These cross talk interactions are also considered with the help of theoretical methods, providing new tools to investigate the molecular-plasmonic coupling. Such experimental and theoretical advances are very promising in the field of innovative and multifunctional hybrid nanomaterials.

DOI： 10.1007/978-4-431-56544-4_22

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We prepared stable nanodispersions of a fluorescent perylenediimide (PDI) derivative having long alkyl chains by nanosecond laser fragmentation of its microcrystalline powder in acetonitrile (ACN). The nanoparticles had cube-like or rod shapes with a mean size of 100 nm, and they dispersed stably for longer than 1 month. The prepared nanobricks exhibited absorption and fluorescence spectra characteristic of one-dimensional aggregates with cofacial stacking of PDI planes. Single-particle fluorescence measurements demonstrated that nanobricks had a well-aligned structure of one-dimensional columns of PDI. The aqueous dispersions were also fabricated by redispersing the prepared nanobricks, utilizing lipophilic interactions of surfactants having long alkyl chains. We examined the fluorescence properties of nanoparticles dispersed in ACN and in water, and observed amplified fluorescence quenching by the surface-adsorbed dye.

DOI： 10.1002/cphc.201601413

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We prepared stable nanodispersions of a fluorescent perylenediimide (PDI) derivative having long alkyl chains by nanosecond laser fragmentation of its microcrystalline powder in acetonitrile (ACN). The nanoparticles had cube-like or rod shapes with a mean size of 100 nm, and they dispersed stably for longer than 1 month. The prepared nanobricks exhibited absorption and fluorescence spectra characteristic of one-dimensional aggregates with cofacial stacking of PDI planes. Single-particle fluorescence measurements demonstrated that nanobricks had a well-aligned structure of one-dimensional columns of PDI. The aqueous dispersions were also fabricated by redispersing the prepared nanobricks, utilizing lipophilic interactions of surfactants having long alkyl chains. We examined the fluorescence properties of nanoparticles dispersed in ACN and in water, and observed amplified fluorescence quenching by the surface-adsorbed dye.

DOI： 10.1002/cphc.201601413

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In this paper, the combination of Two-Dimensional COrrelation Spectroscopy (2D-COS) and Multivariate Curve Resolution Alternating Least Squares (MCR-ALS) is proposed to disentangle absorption and scattering contributions from extinction spectra collected during the synthesis of organic nanoparticles by laser ablation. This procedure relies on the fact that these contributions exhibit distinct dynamics in the synchronous and asynchronous modes of 2D-COS as the ablation proceeds. Thus, initial estimates for absorption and scattering spectral features can be discriminated and subsequently used when applying MCR-ALS analysis. The feasibility and the potential of this approach are demonstrated on a set of extinction spectra collected at different time intervals during the synthesis of dendronized perylenediimide (DPDI) nanoparticles. The time-dependent concentration profiles and spectra obtained provide valuable insights into the relative dynamics of its absorption and scattering. These results allow discussing the formation mechanism of DPDI nanoparticles.

DOI： 10.1016/j.chemolab.2016.11.011

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

Introducing chirality into photomechanical crystals is beneficial for the diversification of mechanical motion. Measurement of the chiroptical and optical anisotropic properties of chiral crystals is indispensable for evaluating photomechanical crystals. The platelike crystals of S- and R-enantiomers of photochromic N-3,5-di-tert-butylsalicylidene-1-phenylethylamine in enol form (enol-(S)-1 and enol-(R)-1) caused bending motion with twisting upon ultraviolet (UV) light irradiation, due to shrinkage along the length and width directions of the irradiated surface, based on the optimized crystal structure of the photoisomerized trans-keto-(S)-1. By employing the generalized high-accuracy universal polarimeter (G-HAUP), optical anisotropic (linear birefringence, LB
linear dichroism, LD) as well as chiroptical (circular birefringence, CB
circular dichroism, CD) spectra of both the enantiomeric crystals on the (001) face were simultaneously measured before and under continuous UV irradiation. The LD peak was observed at 330 nm in the negative sign, derived from the π-π∗ transition of the intramolecularly hydrogen-bonded salicylidenimino moiety. The CD spectra of the S and R crystals revealed the negative and positive Cotton effect at 330 nm, respectively, and new peaks appeared at 460 nm under UV light irradiation due to photoisomerization to the S and R trans-keto isomers at around 10% conversion. The CB and CD spectra evaluated by the HAUP measurement were opposite to those measured in the hexane solution, as well as those simulated by quantum chemical calculation. The dissymmetry parameter, g, of the enol-(S)-1 crystal along the c axis (0.013) was approximately 10 times larger than the g values in the solution (0.0010) and by calculation (0.0016).

DOI： 10.1021/jacs.6b09633

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have developed a femtosecond pump probe light scattering microspectroscopic system in which the output of a femtosecond Ti:sapphire oscillator (1 W, 82 MHz) was used as a light source; the pump light is the second harmonics (395 nm) of the laser output, and the probe light is a femtosecond white-light continuum (490-900 nm) generated with a photonic crystal fiber. Detection of the backscattered light from single nanoparticle on a glass substrate allowed us to obtain higher gain of the transient signals by similar to 20 times in comparison with the conventional transmittance-mode experiment. This high-sensitivity of the back scattering detection makes it possible to examine ultrafast relaxation dynamics of excited states in organic nanoparticles, which, in general, are lower photodurability than the inorganic one. We applied the system to single nanocrystals of a-form perylene and then succeeded in direct observation of the excimer formation dynamics on a picosecond time scale. Single nanoparticle measurements for the perylene nanocrystals having a size range of 100 to 500 nm suggested that the excimer formation time became short from 2 ps to &lt;0.3 ps for decreasing of the size.

DOI： 10.1021/acs.jpclett.6b01330

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Solvent polarity dependence of photochromic reactions such as cyclization and cycloreversion of a photochromic diarylethene derivative, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene, was investigated by steady-state spectroscopic and femtosecond laser photolysis methods. For the cyclization reaction, it was revealed that the quantum yield decreased with an increase in solvent polarities, mainly due to the decrease in the fraction of the conformer with C-2 symmetry favorable for the cyclization. This result indicated that the branching ratio for the cyclization and the deactivation to the open-ring isomer at the conical intersection was almost independent of the solvent polarity. On the other hand, it was found for the cycloreversion process that the closed-ring isomer in the S-1 state rapidly deactivated into the ground state in competition with the activated process leading to the conical intersection providing a pathway toward both open- and closed-ring minima in the ground state. The cycloreversion reaction quantum yield also decreasing with an increase in the solvent polarity was attributed to larger increase of the direct deactivation into the ground state from the excited state minimum of the closed-ring isomer.

DOI： 10.1021/acs.jpcc.5b08504

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The photomechanical bending of crystals of a stilbene-type compound substituted with anthracene and indanone groups, (E)-2-(9-anthrylmethylene)-1-indanone (trans-1), was investigated. When a narrow plate-like microcrystal was irradiated with ultraviolet (UV) light at 365 nm, the crystal gradually bent away from the light source and finally reached a semicircular shape after more than 10 min. A larger rod-like crystal, approximately 10 mm in length, also exhibited a slight bending motion. The cessation of UV irradiation caused the bent crystals to return very slowly to their straight form. In the crystals, the anthracene planes of two neighbouring trans-1 molecules are arranged in a head-to-tail parallel manner, with a short plane-to-plane distance of only 3.72 angstrom. The H-1 nuclear magnetic resonance spectra of trans-1 crystals before and after UV irradiation revealed the intermolecular [4 + 4] photodimerisation of the two anthracene planes, while the trans-to-cis photoisomerisation was not significant. The UV-vis absorption spectra of the trans-1 powder crystals, obtained using a diffuse reflectance spectrophotometer, showed a gradual increase in absorbance between 200 and 500 nm with increasing UV irradiation time, reaching a maximum after 1 h. Thermal back-monomerisation was very slow in the dark, not recovering the initial spectrum even after 25 days. The fluorescence spectra at 570 nm, derived from the anthracene excimer, decreased in intensity with increasing UV irradiation time due to a decrease in the amount of anthracene chromophore via photodimerisation. In situ X-ray measurements revealed that the bending of the crystals was caused by slight elongation of the b axis of the unit cell, corresponding to the long axis of the rod-like crystals. Calculations revealed that the observed crystal elongation could be explained by an optimised head-to-tail [4 + 4] orientation of the anthracene dimer.

DOI： 10.1039/c6ce00848h

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We have investigated the excitation intensity dependence of the singlet fission in a crystalline rubrene by means of femtosecond transient absorption microspectroscopy. When a rubrene microcrystal was excited to higher energy levels than that of the lowest singlet excited (S-1) state with a 397 nm femtosecond laser pulse, a triplet excited state was formed through two pathways of the singlet fission, i.e. the direct fission from higher vibrational levels of the S-1 state with a time constant of 2.2 ps and the thermally activated fission from the S-1 state in a few tens of ps. The time constant of the thermally activated fission changed from 35 to 17 ps for increasing of the laser fluence from 0.65 to 18 mJ cm(-2) per pulse, although that of the direct fission was constant with the excitation laser intensity. On the other hand, the yield of the triplet formation was independent of the intensity. We also examined the temperature dependence of the singlet fission and demonstrated the activation energy of the thermally activated fission to be 0.21 eV. Based on the experimental results, we considered the excitation intensity dependence of the singlet fission of the rubrene crystal in terms of the effect of transient local heating on a ps time scale after femtosecond laser excitation owing to the nonradiative vibrational relaxation from the higher vibrational level to the lower one in the S-1 state.

DOI： 10.1039/c6pp00171h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

DOI： 10.1016/j.apsusc.2015.04.104

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Red fluorescence lamellae in prismatic layers of Pinctada vulgaris shell were investigated. SEM-EDS, XRD, and TG-DTA were utilized to characterize prismatic layers. We found that prismatic layers are calcitic prismatic (CP) layers with rich organic substances. Excitation spectrum for red fluorescence determined by a spectrophotometer indicates that the fluorescent matter in the organic substances is porphyrin compound derivatives. By using a fluorescence microspectroscope, the cross section of CP layers shows red fluorescence forming lamellar pattern. The lamellar pattern consists of red and black parallel zones with a modulation of emission intensity. Elemental mapping show a correlation of the fluorescence intensity decay with sulphur-rich zones occupying the CP layers in the black zones. (C)2014 Optical Society of America

DOI： 10.1364/OME.4.001813

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Three 1,2-bis(2-alkyl-1-benzothiophene-3-yl)perhydrocyclopentenes with different alkyl chain lengths (methyl, ethyl, and propyl) at the reactive carbons were synthesized, and their photophysical properties were compared with those of 1,2-bis(2-alkyl-1-benzothiophene-3-yl)perfluorocyclopentenes. The structures of the perhydrocyclopentenes were analyzed by X-ray crystallography, and their cyclization/cycloreversion reaction and fluorescence quantum yields, and fluorescence lifetimes were measured by steady-state spectroscopy and the time-correlated single photon counting method, respectively. From these results, we found the following three differences between perhydrocyclopentenes and perfluorocyclopentenes. (1) For the closed-ring isomers, the absorption bands of the perhydrocyclopentenes (around 450 nm) shifted to a shorter wavelength than those of the perfluorocyclopentenes (around 530 nm) because of the acceptor nature of the perfluorocyclopentene moiety. (2) The cyclization/cycloreversion quantum yields of the perhydrocyclopentenes were slightly larger than those of the perfluorocyclopentenes in hexane. (3) Interestingly, the fluorescence of both the open- and closed-ring isomers was observed only for the perhydrocyclopentenes, and the lifetimes of the closed-ring isomers were estimated to be &lt;30 ps. The fluorescence of the closed-ring isomers of the perhydrocyclopentenes was mainly due to the suppression of nonradiative deactivation from the excited state directly to the ground state compared with the perfluorocyclopentenes. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2014.04.007

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The upconversion luminescence of Y2O3:Er,Yb nanoparticles was observed by an optical microscope, and in-situ measurement of the upconversion spectra in a single particle level was performed. The nanoparticles were prepared by laser ablation in liquid. The target material was synthesized by a precipitation method and sintered at 1250°C. The particle size of the prepared nanoparticles was a few hundred nm. In the upconversion spectra, the red luminescence (4F9/2 → 4I15/2) of the nanoparticles was stronger than their green luminescence (2H11/2/4S3/2 → 4I15/2), while the red luminescence of the target material was weaker than its green luminescence. Because nanoparticles have a large specific surface area, the groups with high phonon energy on the surface accelerate the nonradiative relaxation of the red luminescence process. Fragmentation of target material by laser ablation in liquid led to the increase in the ratio of red to green luminescence.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Pd-mediated polymerization of 1-pyrenylmethyl diazoacetates affords poly(1-pyrenylmethoxycarbonylmethylene) (poly4′), whose CC main chain is tightly surrounded by pyrene groups. The intensity ratio of excimer emission to monomer emission (IE/I M) of poly4′ was more than 20 times higher than that of its vinyl polymer counterpart of poly(1-pyrenylmethyl methacrylate) (polyPyrMA), clearly demonstrating much higher efficiency for excimer formation in poly4′, because of the tight arrangement of the pyrene groups around the main chain. Copyright © 2012 Wiley Periodicals, Inc.

DOI： 10.1002/pola.26480

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Hybrid materials combining gold nanoparticles (GNP) of variable diameter and an organic thin layer of photochromic diarylethenes were achieved. Solid-state photoswitching based on ring-closure/ring-opening reaction was carried out under alternate UV and visible irradiations. In addition to the spectral changes due to the photochromism itself, the surface plasmon resonance related to the GNP is significantly modified, influenced by a photoinduced change in the refractive index of its environment. These two contributions were sorted out, showing the possibility of probing a photochromic switch by following the plasmon band. The shape change of the plasmon band was consistently compared to calculations based on the Mie theory. Additionally, with one given diarylethene compound, both UV-visible spectroscopy and surface enhanced Raman scattering (SERS) spectroscopy showed an acceleration of the ring-opening photochromic reaction in the presence of GNP.

DOI： 10.1039/c3cp50770j

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The fabrication of silver nanoparticles covered with polymers with a well-defined coreshell structure and the quantitative evaluation of the plasmonic enhancement effect on a photochemical reaction in the vicinity of these silver nanoparticles individually dispersed in a medium are described. The photocycloreversion reaction of a diarylethene polymer in the vicinity of silver nanoparticles was enhanced by 2-6 times relative to the reaction without the nanoparticles. The promotion of the photocycloreversion reaction is due to enhancement of the electromagnetic field near the surface of the silver core.

DOI： 10.1002/cphc.201200442

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Femtosecond transient absorption dynamics of C-60 nanoparticles in pure water revealed a strong quenching of the singlet excited state, independent of the excitation light intensity on a 10-ps time scale, and an extremely low yield of the triplet state of C-60 nanoparticles upon photoexcitation.

DOI： 10.1246/cl.2012.1104

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

Dispersions of reduced tungsten oxide and tungsten bronze nanoparticles are known to show a remarkable absorption of near-infrared (NIR) light applicable to solar control filters for automotive and architectural windows. Origin of the NIR absorption has been investigated by analyzing dielectric constants of CsxWO3 (x = 0.15, 0.25, and 0.33) and WO2.72, and using Mie scattering theory. The optical analysis and Mie scattering theory analysis indicate that a localized surface plasmon resonance and polarons of localized electrons contribute alongside to the observed NIR absorption at different wavelengths.

DOI： 10.1557/jmr.2012.25

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

In this work, a simple method for fabricating gold nanoparticle (AuNP) layer on a poly(dimethylsiloxane) (PDMS) substrate based on electrostatic deposition of AuNP colloid onto a chemically-modified PDMS surface using 3-aminopropyltriethoxysilane (gamma-APTES) was developed. AuNPs of 100 nm diameter were successfully dispersed and deposited onto the chemically-modified PDMS surface. The morphology and optical property of the AuNP layer were examined by atomic force microscopy (AFM) and UV-visible absorption spectroscopy, respectively. It was found that the prepared AuNP layer on PDMS could work as a localized surface plasma resonance (LSPR) sensor. The sensing characteristics were examined by changing the refractive index of solution surrounding the AuNP and antigen-antibody events on the AuNP surface. Changes in absorbance intensity and peak wavelength shift of the LSPR band were both clearly observed. The developed technique can hopefully expand the applications of PDMS for not only micro channel fabrication, but also sensing construction for easier and simpler preparation of microfluidic biosensors, which were then applied for immunoassays and other biochemical analyses. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.037001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

We newly synthesized various sized gold nanoparticles covered with photochromic polymers consisting of diarylethenes with various structures to investigate an effect of the gold nanoparticles on the photocycloreversion reaction of the diarylethene chromophores upon irradiation with visible light. The gold nanoparticles covered with the photochromic polymers exhibited reversible changes in localized surface plasmon resonance (LSPR) absorption along with the photochromic reaction depending on the diameter of the particle, the distance between the gold surface and the chromophore, and the structure of the diarylethene chromophore. The rate of the photocycloreversion reaction of the chromophores around the particle was enhanced by the gold nanoparticles and the degree of the enhancement was affected by the diameter of the particle and the distance from the gold surface, while a structural difference in the diarylethene chromophore had no effect on the degree of the enhancement. The larger enhancement of the photocycloreversion reaction was observed by irradiation at longer wavelength side than visible light corresponding to the LSPR frequency.

DOI： 10.1039/c2cp23820a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The photochromic reactivity of diarylethene polymers attached to gold nanoparticle in the solid state was investigated. The photochromic diarylethene polymers around the gold nanoparticle exhibited reversible photochromism upon alternating irradiation with ultraviolet (UV) and visible light even in the solid state. The local surface plasmon resonance (LSPR) band of the gold nanoparticle in the solid state was red-shifted in comparison with that dispersed in a solution because of the closer interparticle distance. Alternating irradiation with UV and visible light led to the photoreversible changes in the LSPR band because the refractive index of the diarylethene polymer shell changes along with the photochromic reaction of the diarylethene polymers. However, the behavior of the spectral changes significantly depended on the irradiation wavelength. It reveals that the photocycloreversion reaction heterogeneously took place in the shell of the diarylethene polymers upon irradiation at longer wavelength to be enhanced in proximity to the gold nanoparticles. The promotion of the photoreaction is due to the plasmonic enhancement effect both in the vicinity and in the gap of the gold nanoparticles. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2011.03.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Modification of the excimer emission of N,N'-bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylene dicarboximide (PDI) by localized surface plasmon resonance (LSPR) of silver nanocubes (SNCs) 100-170nm in size was investigated by single-particle spectroscopy. SNCs were immobilized on a glass substrate and then covered with a 20-nm-thick PDI film via vacuum vapor deposition. Using fluorescence microscopy to compare areas with and without single SNCs on the same sample, we demonstrated the enhanced intensity and modulated spectral shape of the excimer emission by single SNCs. The excimer emission modification was examined for various sizes of SNCs and different LSPR peak positions, and the electromagnetic field enhancement effect on the radiation emission process was discussed. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2011.03.013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The photocycloreversion reaction of a diarylethene upon irradiation with visible light was found to be accelerated in proximity to a gold nanoparticle covered with diarylethene polymers (Au-poly(DE)) dispersed in a solution. Enhancement of the reaction rate by the gold nanoparticle was quantitatively evaluated by kinetic analysis on the basis of absorption spectroscopy. Multicomponent bleaching of the dosed-ring form of poly(DE) was observed around the gold nanoparticle upon irradiation with visible light; the irradiation time dependence of the absorbance could be explained using a reaction model with two decay components rather than one. The results indicate that the cycloreversion reaction was enhanced only in the vicinity of the gold nanoparticle:. The faster reaction inside the polymer shell was confirmed by numerical spectral simulation of Au-poly(DE) using a double shell model based on Mie theory. The enhancement factor determined as the ratio of the enhanced reaction rate to the nonenhanced rate was estimated to be 2-5, and the enhanced region was evaluated to be 9-12 nm from the surface of the gold nanoparticle. The enhancement factor tended to increase with irradiation at longer incident wavelength, which did not correlate with the spectral shape of the local surface plasmon resonance (LSPR) band of the gold nanoparticle.

DOI： 10.1021/jp111807k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Stable aqueous colloids of 10-nm sized organic nanoparticles were tailored by laser ablation of microcrystalline quinacridone in water. The nanocolloids were flaky in shape and had the dimension of a width of 13 (+/- 5) nm and a height of 1.4 (+/- 0.5) nm. The formation mechanism is discussed in terms of laser-induced fragmentation of organic solids and the potential application of aqueous organic nanocolloids free from any additives and chemicals is considered. DOI 10.1002/tcr.201000024

DOI： 10.1002/tcr.201000024

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Quinacridone nanoparticles with a mean size of about 200 nm are successfully prepared using nanosecond near-infrared (NIR) laser ablation of its microcrystalline powders in heavy water. The absorption spectra of the formed colloidal solutions depend on the excitation wavelengths, which is eventually ascribed to number and energy of absorbed photons. beta-carotene has low photostability and is easily decomposed upon UV/VIS laser ablation of its solid, while its nanoparticles are prepared utilizing this NIR laser ablation technique. The advantage of nanoparticle preparation by NIR laser ablation is discussed.

DOI： 10.1007/s00339-010-5922-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have studied the photochromic reaction of p-hydroxycinnamic-thiophenyl ester in the microcrystalline state We attributed the fluorescence spectral evolution of the microcrystal under UV irradiation to the photoinduced trans-to-cis isomerization The photocyclic behavior of the chromophore was demonstrated by cis-to-trans back reaction under a subsequent visible light irradiation In addition the [2 2] topochemical photocyclodimer was observed as another photoproduct It is considered that the cooperative photoisomerization is initiated at the local lattice distortion and free spaces around the [2 + 2] cyclodimer near the crystal sui lace and the photoisomerization induces larger lattice deformation and further photoisomerization in the interior of the crystal

DOI： 10.1021/jp909850r

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MATERIALS RESEARCH SOC  

Optical absorption and scattering behaviors of lanthanum hexaboride (LaB(6)) nanoparticulate dispersion coatings with various particle sizes have been investigated in the ultraviolet to near-infrared (NIR) wavelengths for application to solar control filters. Large characteristic near-infrared absorption is introduced as the decreased particle size falls into nanoscale, and its origin is discussed in terms of a localized surface plasmon resonance (LSPR) of conduction electrons. Optical constants of LaB(6) have been measured and Mie scattering theory analysis was conducted. The theory was found to generally replicate the optical characteristics, and variations of absorbed and scattered wave fractions as well as the LSPR wavelength have been discussed with varying particle size. The absorption peaks are found as shaped narrower and located at shorter wavelength in theory than in experiment, which is suggested as ascribed mainly to the nonspherical distorted shape of LaB(6) nanoparticles.

DOI： 10.1557/JMR.2010.0075

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MATERIALS RESEARCH SOC  

Optical absorption and scattering behaviors of lanthanum hexaboride (LaB(6)) nanoparticulate dispersion coatings with various particle sizes have been investigated in the ultraviolet to near-infrared (NIR) wavelengths for application to solar control filters. Large characteristic near-infrared absorption is introduced as the decreased particle size falls into nanoscale, and its origin is discussed in terms of a localized surface plasmon resonance (LSPR) of conduction electrons. Optical constants of LaB(6) have been measured and Mie scattering theory analysis was conducted. The theory was found to generally replicate the optical characteristics, and variations of absorbed and scattered wave fractions as well as the LSPR wavelength have been discussed with varying particle size. The absorption peaks are found as shaped narrower and located at shorter wavelength in theory than in experiment, which is suggested as ascribed mainly to the nonspherical distorted shape of LaB(6) nanoparticles.

DOI： 10.1557/JMR.2010.0075

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Fluorescent nanoparticles of N,N'-bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenedicarboximide (DBPI) were fabricated by laser ablation of its microcrystals dispersed in pure water, and their optical extinction and fluorescence spectra were investigated. Colloidal nanoparticles withmean sizes of 30 to 80nm were prepared without molecular decomposition by tuning the fluence of the irradiating laser. Spectral simulation based on Mie theory explains the difference in the absorption spectra of the nanoparticles and a DBPI vapor-deposited film. The fluorescence of the nanoparticle colloids showed a monomer-like emission band with a vibrational structure, while the initial microcrystals exhibited a broad excimer band. These results indicate that the DBPI nanoparticles have crystal morphologies different from those of microcrystals. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.49.06GJ04

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Language：English   Publishing type：Part of collection (book)   Publisher：John Wiley and Sons  

DOI： 10.1002/9783527627820.ch28

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Various sizes of gold nanoparticles covered with photochromic diarylethene polymers (Au-poly(DE)s) were prepared by Brust's method, citrate reduction, or a seeding growth method. The diarylethene polymers oil the particles exhibited reversible photochromism upon alternating irradiation with ultraviolet and visible light, both in solution and in the solid state. Au-poly(DE) of larger size, prepared by the seeding growth method, showed a significant shift in the local surface plasmon resonance (LSPR) band photoreversibly as a result of photochromic reaction of the diarylethene polymers around the gold nanoparticles. This change is due to a change in the refractive index of the photochromic chromophore and is remarkably enhanced in the solid state, However, the smaller sized Au-poly(DE) prepared by Brust's method hardly showed my such spectral shift. These results are qualitatively reproduced by a theoretical simulation, which indicates that the sensitivity of the LSPR band strongly depends on the particle size of the gold nanoparticle. The Au-poly(DE)s can be potentially used as new types of plasmonic materials with a light-controllable LSPR band.

DOI： 10.1021/jp906371k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

C-60 aqueous nanocolloids were prepared by irradiating a suspended aqueous solution of C-60 with intense nanosecond 532 and 355 nm laser pulses. The initial submicron crystal of C-60 was fragmented into nanoparticles, resulting in a transparent yellow solution which was followed by UV/vis absorption spectroscopy. The obtained absorption spectra were similar to those for C-60 bulk film and its nanoparticles, which have a size on the order of 10 nm, and their formation had thresholds with respect to laser fluence. The nanoparticles were confirmed by their SEM observation and by examining the centrifuging effect on the colloids, while possible photochemical decomposition was excluded by C-13 NMR analysis of 1,2-dichlorobenzene-d(4) solution, where the possible products can be dissolved in addition to C-60 nanoparticles. The present result is the first demonstration of the preparation of pure and very stable C-60 aqueous nanocolloids without any additives. The formation mechanism and potential application to biological testing and toxicity are discussed. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2009.01.015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Photodynamics and excited-state intramolecular proton transfer (ESIPT) of N-(3,5-ditert-butylsalicylidene)-4-aminopyridine (4P) and N-(3,5-ditert-butylsalicylidene)-2-aminopyridine (2P) are studied by steady-state and transient optical spectroscopy in solution and solid state (microcrystalline powder). These two compounds are representative of anils Classes A and B, respectively. The results confirm that in solution both compounds have a similar dynamic behavior: upon excitation at 390 nm, ESIPT leads to different cis-keto* fluorescent species which relax to the photochromic trans-keto photoproduct within a few tens of picoseconds. Furthermore, for the first time, picosecond data are recorded for the two classes of anils in the solid state: in 2P, two cis-keto* fluorescent excited state species (23 and 250 ps lifetime) are relaxing exclusively to the cis-keto ground state, whereas in 4P, a single cis-keto* fluorescent species is observed which leads to the trans-keto photoproduct in 250 ps via an intermediate metastable species.

DOI： 10.1021/jp901849a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Using a confocal Rayleigh light scattering microspectroscopy and imaging system, we followed and recorded the scattering spectra of single gold nanoparticles interacting with living mouse fibroblast cells, during the scale of I h. A white light continuum produced by a femtosecond laser was focused on gold nanoparticles with a diameter of 80 nm, while an incubation system ensured viability of the living cells. After reporting spectral characteristics of gold nanoparticles and their target fibroblasts, separately and in combination, tracking sequences of single nanoparticles in contact with a single cell are described. Through the study of three separate and representative cases, transitory as well as plasmon resonance band shifts, which can be linked to biological events, have been observed and are discussed here.

DOI： 10.1021/jp9018124

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Language：English   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/jp903929e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOCIETY APPLIED PHYSICS  

Fluorescent nanoparticles of dendronized perylenediimide (DPDI) were fabricated by laser ablation in water. We succeeded in the preparation of colloidal nanoparticles of different sizes (150-400 nm) and examined their size-dependent optical absorption and fluorescence properties. The size-dependent extinction spectra can be explained by the effect of light scattering loss, and it was confirmed that their absorption spectrum is similar to that of molecules in solution. The very weak interchromophoric interaction is also confirmed by fluorescence spectral measurement. On the other hand, we found that the fluorescence quantum yield decreases with decreasing of the particle size, and we propose a new mechanism for the size-dependent reduction of emission intensity in organic nanoparticles. On the basis of the size dependent-fluorescence quantum yield and solvent polarity dependence of DPDI fluorescence in organic solvents, we considered that, while the interchromophoric interactions are weak in the nanoparticle, the excited singlet state migrates in a nanoparticle owing to energy hopping and is quenched at the surface, leading to the observed size-dependent fluorescence quantum yield (Phi(f)) and a smaller value of Of for nanoparticles than for the molecules in nonpolar solvents. (C) 2009 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.48.065002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

We studied the enhancement of excimer emission from a thin perylene dye film (10-nm thickness) by localized surface plasmon resonance (LSPR) of single gold nanoparticles (GNPs), and observed a large fluorescence enhancement factor of about 25. The absence of excitation wavelength dependence of the enhancement factor indicates that the fluorescence intensity enhancement is mainly due to an increase of the radiative emission rate by LSPR.

DOI： 10.1246/cl.2009.332

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A new photochromic diarylethene, 1,2-bis(5'-ethoxy-2'-(2'-pyridyl) thiazolyl) perfluorocyclopentene (1), is synthesized. Nanoparticles are obtained by laser ablation at both 355 and 532 nm, corresponding to the absorption wavelengths of open and the closed forms. 1 can be reversibly photoswitched in various states: organic solution, bulk crystal, nanoparticle colloidal solution, and single nanoparticle, as demonstrated by dark-field scattering spectroscopy.

DOI： 10.1002/adma.200801578

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Laser ablation of microcrystals dispersed in a poor solvent, leading to nanoparticle preparation, was examined by changing laser fluence and shot number, and its mechanism was considered. Femtosecond laser-induced crystallization of urea was followed by measuring imaging, optical scattering, and SHG detection, and its dynamics was clarified.

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Language：English   Publisher：AMER CHEMICAL SOC  

In working with nanoparticles, researchers still face two fundamental challenges: how to fabricate the nanoparticles with controlled size and shape and how to characterize them. In this Account, we describe recent advances in laser technology both for the synthesis of organic nanoparticles and for their analysis by single nanoparticle spectroscopy.
Laser ablation of organic microcrystalline powders in a poor solvent has opened new horizons for the synthesis of nanoparticles because the powder sample is converted directly into a stable colloidal solution without additives and chemicals. By tuning laser wavelength, pulse width, laser fluence, and total shot number, we could control the size and phase of the nanoparticles. For example, we describe nanoparticle formation of quinacridone, a well-known red pigment, in water. By modifying the length of time that the sample is excited by the laser, we could control the particle size (30-120 nm) for nanosecond excitation down to 13 nm for femtosecond irradiation. We prepared beta- and gamma-phase nanoparticles from the microcrystal with beta-phase by changing laser wavelength and fluence. We present further results from nanciparticles produced from several dyes, C-60, and an anticancer drug. All the prepared colloidal solutions were transparent and highly dispersive. Such materials could be used for nanoscale device development and for biomedical and environmental applications.
We also demonstrated the utility of single nanoparticle spectroscopic analysis in the characterization of organic nanoparticles. The optical properties of these organic nanoparticles depend on their size within the range from a few tens to a few hundred nanometers. We observed perylene nanoscrystals using single-particle spectroscopy coupled with atomic force microscopy. Based on these experiments, we proposed empirical equations explaining their size-dependent fluorescence spectra. We attribute the size effect to the change in elastic properties of the nanocrystal. Based on the results for nanoparticles of polymers and other molecules with flexible conformations, we assert that size-dependent optical properties are common for organic nanoparticles. While "electronic confinement" explains the size-dependent properties of inorganic nanoparticles, we propose "structural confinement" as an analogous paradigm for organic nanoparticles.

DOI： 10.1021/ar800125s

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This letter reports the optical microscopy characterization of gold nanoparticle-doped zeolite L crystals prepared by applying two key techniques: laser ablation and crystallization inclusion. The former allowed the stable formation of Au NPs in the synthesis gel, while the latter permitted the encapsulation of Au NPs exceeding the pore openings of the zeolite crystals, still maintaining the crystal structure as a whole. The microscopy characterization was performed by exploiting single particle light scattering spectroscopy and imaging techniques which offered the Rayleigh scattering images of individual An particles within the crystals and the scattering spectra ascribable to the surface plasmon resonance band of Au NPs embedded. This is a unique demonstration for the application of laser ablation-induced NPs in solution to practical use for fabricating a nanocomposite material. Furthermore, the present results revealed that the dark field microscopy is capable of visualizing metal nanoparticles as small as 40 nm diameter confined in the light scattering crystalline medium.

DOI： 10.1021/jp8063189

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

An impulsive force, which was generated by focusing tightly a femtosecond laser into a cell culture medium, was applied to inject nanoparticles into local areas of a single mouse fibroblast NIH3T3 cell. When the impulsive force was induced near the cell, the nanoparticles adhering on the cell membrane were introduced, which was directly confirmed by confocal fluorescence microscopy.

DOI： 10.1007/s00339-008-4637-5

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Highly fluorescent organic nanoparticles with size of about 300 nm were prepared by nanosecond laser ablation of micrometer-sized powder of dendronized perylenediimide dispersed in water. The nanoparticle colloidal solution provided a fluorescence quantum yield of 0.58. The absorption and emission spectral studies demonstrated that the bulky dendron groups at the side bays of perylenediimide chromophore efficiently suppress the interchromophoric interactions in the nanoparticles. Fluorescence measurement on several single nanoparticles underlines that the prepared nanoparticles are bright and photo-stable enough to be a useful probe for single particle fluorescence investigation.

DOI： 10.1007/s00339-008-4661-5

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DOI： 10.1017/S1431927608084377

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：POLISH CHEMICAL SOC  

Single particle fluorescence spectroscopy coupled with AFM observation is reported for perylene nanocrystals. Fluorescence spectral measurement for individual nanocrystals with the size from 100 nm to 500 nm and fluorescence anisotropy analysis demonstrate that the size dependence in fluorescence is in the intrinsic nature of nanometer-sized crystal of perylene. Single nanoparticle fluorescence shows the enhanced monomer (M-) emission compared to the bulk crystal and a blue-shift of excimer (E-) emission peak wavelength by decreasing the nanoparticle size. It is found for the first time that the size dependence is correlated well to the surface-to-volume. ratio of nanocrystal. The size-dependent fluorescence is not attributed to a quantum confinement effect of exciton, but to a change in the elastic properties of nanocrystal with size, which in turn affects excimer formation. We-discuss the decrease in elastic constant of crystalline lattice due to large surface-to-volume ratio, and propose an empirical formula on the size-dependence of E-emission peak in the framework of the strong coupling model of exciton-phonon interaction.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/LEOSST.2008.4590492

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We have prepared nanoparticles of five organic dye molecules by laser ablation of their microcrystals in poor solvents using the third harmonics of nanosecond Nd3+:YAG laser as an excitation light source. Their colloidal solutions were stable for longer than I week without any surfactants. The mean size was almost common to all the dyes (about 50 nm) and its distribution was narrow, which was confirmed by SEM observation. By applying electrophoretic deposition, the homogeneous thin film of quinacridone nanoparticles was fabricated on an indium-tin-oxide electrode. It was demonstrated that the films with different grain size and crystalline phase can be fabricated arbitrarily by using different nanoparticles. Laser ablation is also useful for crystallization of organic molecules, which was demonstrated for a representative organic nonlinear optical material.

DOI： 10.1117/12.771175

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOHN WILEY & SONS LTD  

Vapor deposition method was used to obtain nanocrystals of N-(3,5-di-tert-butylsalicylidene)-4-aminopyridine (1) and N-(3,5-di-tert-butylsalicylidene)-4-iodoaniline (2), and nanoscale thin layers (65 nm thick) of cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (3). Compound 3 was also deposited on a substrate previously covered by gold nanoparticles (phi = 100 nm). Nanoscale crystals of 1 and 2 showed similarities with bulk crystals: they exhibit photochromic properties and they have similar shapes according to Atomic force microscopy (AFM) investigations. The thin layers of 3, with and without gold nanoparticles, showed light-induced absorption change in the visible. Copyright (c) 2007 John Wiley & Sons, Ltd.

DOI： 10.1002/poc.1226

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have prepared quinacridone (QA) colloids with various particle sizes (25-120 nm) and different crystalline phases by nanosecond laser ablation of its microcrystalline powder dispersed in water and fabricated the prepared colloidal particles into homogeneous films on an indium-tin-oxide electrode by an electrophoretic deposition (EPD) method. The nanoparticle-assembled films consist of closely packed nanoparticles and many nanosized pores. We evaluated the porous nature of the film by scanning electron microscopy observation and by measuring the film thickness dependence of the absorption. It was found that the film morphology is sensitive to the applied bias, and the optimum bias for the QA colloid was determined to be about 10 V/cm. We also demonstrated that organic thin films with different grain sizes and crystalline phases can be fabricated arbitrarily by combining the EPD method with nanoparticle preparation by laser ablation.

DOI： 10.1021/jp074300f

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We have proposed and demonstrated a new methodology for fabricating an interpenetrating network nanostructure toward a highly efficient organic solar cell, utilizing a C60 nanoparticle assembly film on an electrode prepared by electrophoretic deposition (EPD) of its nanoparticle colloid.

DOI： 10.1246/cl.2007.1160

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We prepared quinacridone (QA) nanoparticles with a mean size of 70 run by nanosecond laser ablation of their microcrystalline powder dispersed in water, and assembled the nanoparticle colloid into a thin film on an electrode by electrophoretic deposition (EPD). The EPD film consists of closely packed QA nanoparticles and shows a photoconductive response similar to the conventional organic films by vacuum deposition. The present fabrication technique is expected to be applied to the preparation of organic nanostructure using nanoparticles as building block for novel electronic and optoelectronic device application.

DOI： 10.1143/JJAP.46.L733

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Language：Japanese   Publisher：The Laser Society of Japan  

When a near-infrared (NIR) femtosecond laser is focused in water, several kinds of nonlinear phenomena, such as shockwave propagation, cavitation bubble generation, and jet flow, are induced in the vicinity of the laser focal point. Such phenomena are also induced by near-infrared nanosecond and picosecond lasers, but femtosecond irradiation allows a better localization. Moreover NIR femtosecond laser focussing permits to perform a local processing of cell and tissue because of its efficient multi-photon absorption and photo-mechanical ablation mechanism. In this study, the impulsive force generated in cell culture medium by these nonlinear phenomena was applied to individual control of single animal cells. Mouse NIH-3T3 fibroblast cells cultured on a substrate were independently isolated by the impulsive force, and patterned by transferring them to another substrate. Furthermore nanoparticles and biological molecules are transfected to the cell by the local processing of the cell membrane. These demonstrations are promising for future femtosecond laser methodology for bioscience and biotechnology.

DOI： 10.2184/lsj.35.430

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Other Link： https://jlc.jst.go.jp/DN/JALC/00297670870?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Three-dimensional dissection of a single actin stress fiber in a living cell was performed based on multi-photon absorption of a focused femtosecond laser pulse. The realignment process of an actin stress fiber was investigated after its direct cutting by a single-shot femtosecond laser pulse irradiation by high-speed transmission and fluorescence imaging methods. It was confirmed that mechanical force led by the femtosecond laser cutting propagates to entire cell through the cytockelton in a 100 mu s time scale. The cut actin stress fiber was realigned in the time scale of a few tens of minutes. The dynamic analysis of the realignment induced by single-shot femtosecond laser gives new information on cell activity. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2007.01.047

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Polarization dependence of the second harmonic generation (SHG) was studied on a single crystal of the photochromic N-(3,5-di-tertbutylsalicylidene)-4-aminopyridine (4P). The optimal polarization condition for SHG is obtained when both the fundamental and second harmonic waves are parallel to the main axis of the crystal. This experimental result was correlated with calculations based on X-ray diffraction structure. Also, wavelength dependent studies showed that SHG-switching on near-UV irradiation could be tuned by utilizing the absorption and resonance effects of the photo-induced species. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2007.02.001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A new class of nanostructures were fabricated by one-step hydrothermal reaction of a mixture solution of TiO2 anatase powder and a Sn-porphyrin, trans-dihydroxo[5,10,15,20-tetrakis(p-tolyl)porphyrinato]tin(IV) [SnTTP], and they were found to be well-crystalline trititanate (H2Ti3O7)-type multilayered nanofibers (TiNFs) intercalated by SnTTP which have lengths in the range of 0.5-1 mu m with an average diameter of approximately 50 nm. Based on the femtosecond-diffuse reflectance transient absorption and photoluminescence spectroscopic measurements, the SnTTP-intercalated TiNFs were observed to exhibit efficient optoelectronic properties such as photoinduced electron transfer from deep surface states of trititanate layer to SnTTP, forming an anion radical SnTTP..- rapidly in a few picoseconds. These results infer that electrons and holes are effectively separated in the SnTTP-TiNFs upon illumination, and consequently remarkable UV-visible light-sensitive photocatalytic activities as compared to those of free TiNFs and SnTTP, suggesting that the SnTTP-intercalated TiNFs have potential application in development of efficient artificial photosynthetic systems and photoelectronic materials.

DOI： 10.1021/cm0629863

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The interaction between molecular exciton and localized surface plasmon (LSP) polarization has been investigated by measuring light scattering spectra of single gold nanoparticles coated with cyanine dye J-aggregate. The spectral dip reflecting absorption spectral band of the J-aggregate varies with the particle size and the distance between the J-aggregates and the surface of gold nanoparticles. By comparing the experimental results with theoretical calculations based on the Mie theory, we demonstrate that the LSP polarization affects the peak and shape of the J-aggregate absorption band when the exciton resonance peak locates near the LSP resonance peak and when the separation of the J-aggregate from the metal surafce is short. The modification of the J-aggregate exciton band induced by LSP is considered to be due to strong coupling between the molecular exciton transition and the LSP resonance of metallic nanoparticles.

DOI： 10.1021/jp067565n

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

We investigated the optical properties of the hexagonal/ triangle gold nanoplates by single particle spectroscopy. By comparison with scanning electron microscope (SEM) observations, we successfully demonstrated that light scattering spectra of the hexagonal nanoplates with 360 120-nm edge lengths and the triangular ones of 190 60nm exhibited two peaks in visible-near infrared region corresponding to quadrupole and higher multipole modes of localized surface plasmon resonance (LSPR).

DOI： 10.1246/cl.2007.318

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DOI： 10.1016/S1574-0641(07)80020-9

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DOI： 10.1016/S1574-0641(07)80021-0

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DOI： 10.1016/S1574-0641(07)80029-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CANADIAN SOC ANALYTICAL SCIENCES & SPECTROSCOPY  

The size, shape, and environment dependence of localized surface plasmon resonance (LSPR) from individual Au nanoparticles was investigated using light-scattering microspectroscopy, which is highly-sensitive to the above factors. Here we identified that scattering angle dependence of LSPR bands cannot be completely neglected when the radius of a Ag nanoparticle was larger than 40 nm. This was based on a comparison between calculated Mie-resonance and experimental results of light-scattering spectra. The variations in LSPR bands of Au nanoparticles which were embedded in polymer films were attributed to variations of particle size and shape. Interestingly, we observed twin peaks in the light-scattering spectra of several Au nanoparticles. From correlated polarization light-scattering spectroscopy and scanning electron microscopy analyses, we identified twin peaks that originated from nanoparticle aggregates in which two spheroid particles were touching each other. Also, based on the light-scattering spectroscopy of Au nanoparticles covered with different media, we identified changes of the LSPR bands in different dielectric medium which depended on the nanoparticle shape.

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The authors have developed a laser microfixation technique of J aggregates from pseudoisocyanine solution onto a glass substrate. By focusing a near-infrared (NIR) laser beam into the solution near the glass substrate, conglomerate J aggregates are deposited at the focal point and fixed on the substrate. Fixed J aggregates show a narrower fluorescence band than the deposited one without laser focusing, indicating that highly ordered J aggregates are selectively confined in the laser focus due to optical trapping. Furthermore, they have demonstrated that the orientation of the transition dipole in fixed J aggregates is controlled by the polarization direction of the NIR laser beam. © 2007 American Institute of Physics.

DOI： 10.1063/1.2759468

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WALTER DE GRUYTER GMBH  

Various time- and space-resolved spectroscopies have been developed and applied to thin films and nanoparticles. Dynamic reflection spectroscopies of total internal, diffuse, and regular reflection modes analyze photophysical and photochemical processes at the interface/surface layers with thicknesses of a few tens to a few hundreds of nm and of optically scattering materials. The excited singlet, triplet, and ionic states are identified, and intersystem crossing, isomerization, electron transfer and recombination, and photothermal conversion due to excited-state annihilation are analyzed, just as by transmittance mode spectroscopy. Fluorescence and Rayleigh light-scattering spectroscopies are developed for elucidating excited-state dynamics of single nanoparticles. The optical properties are related to their size, shape, internal structure, and environmental conditions. We prove that organic molecular materials show novel nanometer-size effects due to structural confinement. The high-intensity laser excitation induces ablation whose dynamics and mechanism are considered on the basis of time-resolved spectroscopy and imaging. For nanosecond and femtosecond ablation, we propose cyclic multiphotonic absorption and photomechanical mechanisms, respectively, while purely photochemical ablation was confirmed. Ablation studies have opened a new research approach toward expansion and contraction dynamics of polymer films, nanoparticle preparation, crystal growth control, crystallization in saturated solution, and others.

DOI： 10.1351/pac200678122205

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We have developed a dark-field optical microspectrscopic system coupled with AFM measurement, and applied it to 1, 6-di(N-carbazolyl)-2-4-hexadiyne (DCHD) nanocrystal systems. We revealed clearly the size and shape dependent peak of the polymer-backbone electronic transition of individual poly-DCHD nanocrystals. It was found that the peak energy of the resonant Rayleigh scattering spectra shifted to a lower energy for nanocrystals having larger cross-section against its long axis. In situ observation of photopolymerization of individual monomer DCHD nanocrystals is also descried. It has been successfully demonstrated that the morphological of fibrous nanocrystal changes upon polymerization. Our single particle results demonstrate that far-field microscopy coupled with AFM is a reliable experimental approach for investigating optical properties and photochemistry of organic nanoparticles.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Near-infrared (NIR) femtosecond laser microscope with Cr:Forsterite laser at ca. 1.26 mu m output wavelength was constructed and applied to two-, three- and four-photon imaging of gold nanoparticle and some organic micro crystals. The ultrafast pulse duration of 35 fs after passing through the objectives easily induced higher-order multiphoton absorption. The size of the laser focal spot and the resolution along the optical axis were discussed by comparing the present higher-order multiphoton imaging and two-photon induced processes. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2006.04.014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have studied the photoinduced trans/cis isomerization of the protonated form of p-hydroxycinnamic thiophenyl ester, a model chromophore of the photoactive yellow protein (PYP), in crystalline phase, by both fluorescence and infrared spectroscopies. The conversion from trans to cis configuration is revealed by a shift of the fluorescence peak and by inspection of the infrared maker bands. The crystal packing apparently stabilizes the cis photoproduct, suggesting different environmental effects from the solvent molecules for this model chromophore in liquid solutions or from the amino acid residues for the PYP chromophore.

DOI： 10.1021/jp064984b

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

To investigate the dynamics of photoinduced ring-opening and -closure reactions in crystalline phase, we measured transient absorption spectra of spironaphthooxazine microcrystalline powder by femtosecond diffuse reflectance spectroscopy and examined their temperature dependence. The lifetimes of the excited state of the spiro form and the Subsequent non-planar open form were about 3 ps and 3 ns at room temperature, respectively. The temperature dependence of their decay constant showed the Arrhenius type behavior and the activation energy of the ring-opening and -closure reactions are estimated to 7 and 12 kJ mol(-1), respectively. The yield of the non-planar open form became smaller at lower temperature, and it was zero below about 140 K. The experimental results and kinetic analysis indicate that a short-lived species having a molecular conformation different from the non-planar form should be considered as an intermediate in the ring-opening reaction. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2005.10.034

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Quinacridone (QA) nanoparticles were formed by nanosecond laser ablation of QA microcrystalline powder dispersed in water. The particle size and phase were examined at two different excitation wavelengths of 355 and 580 nm. At a fluence of 95 mJ/cm(2), the mean sizes of the formed nanoparticles were approximately 22 and 50 nm at 355 and 580 nm excitations, respectively. The absorption spectra of the nanoparticles prepared by 355 nm laser pulses showed the caracteristic bands of the initial beta-form QA in the fluence range from 30 to 120 mJ/cm(2). On the other hand, 580 nm laser pulses with fluences of 50 to 118 mJ/cm(2) caused the spectra to become similar to that of gamma-form QA. We demonstrate that the crystalline phase and mean size of QA nanoparticles can be controlled by tuning the intensity and wavelength of laser pulses.

DOI： 10.1143/JJAP.45.384

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Language：English   Publisher：AMER CHEMICAL SOC  

Femtosecond near-infrared laser microscope was developed with a home-built cavity-dumped chromium: forsterite laser as a light source centered at 1.26 mu m. Optimization of the pulse duration achieved 35 fs fwhm at the sample position of the microscope after passing through a 100x objective. This system was applied to the detection of multiphoton fluorescence of some organic microcrystals. Excitation intensity dependence and the interferometric autocorrelation detection of the fluorescence clearly demonstrated that simultaneous three- and four-photon absorption processes are responsible for the production of the excited state for perylene and anthracene microcrystals, respectively. The spatial resolution along the optical axis and its dependence on the order of the multiphoton process were also discussed.

DOI： 10.1021/jp0561165

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DOI： 10.1016/S1574-0641(06)80017-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Microcrystalline powders of spirooxazine and spiropyran compounds do not show photocoloration under steady-state illumination, whereas they undergo photochromism on intense femtosecond loser-pulse excitation. We investigated the characteristic mechanism of the crystalline photochromism by studying the photocoloration of spironaphthooxazine (SNO) and its chloro-substituted derivative (CI-SNO) with our femtosecond diffuse-reflectance spectroscopic system. In particular, femtosecond double-pulse excitation using 390+780-nm pulses and 390+390-nm pulses, with a variable time interval between the two pulses, was applied to reveal an intermediate species involved in the photocoloration. Although 780-nm excitation of an intermediate produced by 390-nm excitation did not lead to isomerization, the 390+390-nm excitation resulted in photocoloration. The yield for SNO decreased on increasing the interval from 40 ps to 5 ns, while that for Cl-SNO was constant. The photocoloration mechanism in the crystalline phase is considered from the viewpoint of the time-dependent density of short-lived transient species, and it is concluded that cooperative interactions of excited states and nonplanar open forms ploy an important role in femtosecond laser-induced photochromism in these crystals.

DOI： 10.1002/cphc.200500251

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Language：English   Publisher：AMER CHEMICAL SOC  

Two new anil molecules exhibiting photochromism in the crystalline state, N-(4-hydroxy)-salicylidene-amino-4-(methylbenzoate) (2) and N-(3,5-di-tert-butylsalicylidene)-4-aminopyridine (3), are obtained. Upon irradiation in the UV, the yellow crystals change color to red, owing to enol-keto intramolecular tautomerism. The red color disappears, when crystals are left in the dark or irradiated with visible light. 3 has the most stable keto form among all anil-type photochromic compounds (tau = 460 days at room temperature). Both exhibit nonlinear optical (NLO) properties and show powder second harmonic generation (SHG) of respectively 10 and 3 times vs urea. X-ray diffraction shows acentric structures where molecules line up "head-to-tail" through hydrogen bonds for 2 (space group Pc), or form a chiral helix 3 (space group P3(2)). Evidence of reversible structural change is given for 3, and we demonstrate the functionality of this crystal as an NLO switching material, as SHG can be photomodulated by about 30%.

DOI： 10.1021/cm050929o

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Organic dye nanoparticles 1-13 nm in height and 10-45 nm in width were prepared by the reprecipitation method. With single-molecule/ nanoparticle spectroscopy, two distinct types of nanoparticles were found: particles with blue emission and particles with red emission. The difference in spectral characteristics is attributed to the presence of two morphological types of particles in the samples. The presence of two types of nanoparticles in the samples was further corroborated by our ability to separate blue nanoparticles from red nanoparticles by centrifugation.

DOI： 10.1021/nl050567j

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SCIENTIFIC PUBLISHERS  

Monodispersed polymer/polydiacetylene composite particles were synthesized by soap-free seeded emulsion polymerization of styrene and methyl methacrylate; the products were characterized by XRD, SEM, TEM, UV-visible spectroscopy, and single particle scattering spectroscopy. In the synthesis process, polycliacetylene nanocrystals were found to act as inhibitor, and consequently a relatively low concentration was necessary. Different monomers lead to the differences in reaction condition and particle morphology; the PMMA composite particles were simpler in preparation than polystyrene particles, but the latter have better spherical morphology. The composite particles were composed of polymer shells and polydiacetylene cores, which kept their crystal structure and optical properties. A high percentage of cored particles could be achieved with optimized reaction conditions where the amount of seed was sufficient and the oily oligomer by-product was suppressed.

DOI： 10.1166/jnn.2005.121

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

This paper reports the dynamics of the photochromic reaction of crystalline N-(3,5di-tert-butylsalicyliden)-4-aminopyridine which can be applied for nonlinear optical photoswitches. The transient absorption spectra of the microcrystalline powder were measured by femtosecond diffuse reflectance spectroscopy and compared with those in ethanol solution. Similar photochromic reaction occurs in solid state and in solution, however some intermediate species were observed before the long lived photoproduct in solid state probably due to steric hindrance in the crystalline state.

DOI： 10.1080/15421400590947351

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：MATERIALS RESEARCH SOCIETY  

This paper presents single particle fluorescence spectroscopy of perylene nanocrystals coupled with AFM observation of their topographic shapes. The fluorescence spectra of individual nanocrystals confirmed clearly and precisely a blue-shift in the excimer emission maximum on the reduction of their volume. The result can be explained in terms of "lattice softening", which makes intermolecular interaction weaker and modified the energy level of the excimer state in nanocrystal.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

Etching dynamics of urethane-urea copolymer film was investigated by utilizing nanosecond time-resolved interferometry and tuning excitation wavelength. From the behavior of fringe pattern deformation at the irradiated areas, it is considered that irradiated polymer film was decomposed more effectively with decrease in excitation wavelength. Excitation wavelength dependence of etching dynamics of urethane-urea copolymer film was not well interpreted in terms of total energy density which was stored within the polymer film due to laser irradiation, while photochemical and photothermal processes can explain mostly the results of shorter wavelength (less than or equal to 475 nm) and longer wavelength (&gt; 530 nm) excitations, respectively.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

The nanosecond transient expansion and successive contraction dynamics of an azobenzene-substituted urethane-urea copolymer film were studied by nanosecond time-resolved interferometry. In addition, the photoisomerization dynamics of azo dyes during morphological change was investigated by transient absorption measurement. A transiently generated cis isomer absorbed a few photons during laser irradiation and its energy was effectively converted to heat. When the pulse width of the irradiated laser was 8 or 14 ns full-width at half maximum (fwhm), the expansion of the polymer film started with 3-6 its delay from the temperature elevation, while the film contracted exponentially accompanying a different absorbance change of the transient species. The expansion dynamics was well explained not in terms of volume change due to isomerization dynamics but in terms of thermal expansion involving glass-rubber transition. The film-thickness-dependent contraction dynamics could be mostly interpreted in view of the heat flow toward the quartz substrate, heat dissipation via the film itself, and phase transition of the polymer film from the rubbery to glassy states. The laser-induced transient morphological change of the urethane-urea copolymer film observed below the threshold could be well explained in terms of nanometer heating and cooling dynamics.

DOI： 10.1143/JJAP.43.5337

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Persistent radical cations can be generated in V ∝ PMO, a periodic mesoporous organosilica incorporating a viologen in its silicate framework. Photoexcitation of V ∝ PMO forms a geminate viologen-halide ion pair that can undergo rapid charge recombination or electron hopping to form the nongeminate ion pair, which persists for minutes (see picture). In contrast, viologen-halide CT complexes in solution undergo complete charge recombination on the sub-nanosecond timescale.

DOI： 10.1002/cphc.200301038

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have investigated size-dependent optical properties of poly-1,6-di(N-carbazolyi)-2,4-hexadiyne (poly-DCHD) nanocrystals in ensemble and in a single particle level. Our experimental results demonstrate that far-field microscopy coupled with an AFM setup is a reliable experimental approach for investigating optical properties of single organic nanoparticles. Single poly-DCHD nanocrystals show resonant Rayleigh scattering spectra with a lower resonance energy peak for nanocrystals having larger cross-section against its long axis. We also examined the extinction and the resonant Rayleigh scattering spectra in ensemble and the resonant Rayleigh and Raman scattering spectra and their anisotropy of single nanocrystals. The results indicate that the size-dependent resonance peak of the polymer-backbone electronic transition can be ascribed to structural confinement of nanocrystals, which reduces the effective conjugation length of pi-clectron in the polymer backbone for nanocrystals with a small cross-section.

DOI： 10.1021/jp031369o

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

We have succeeded in preparing oxo(phtalocyaninato)vanadium (IV) (VOPc) nanoparticles dispersed in water by femtosecond laser ablation of its bulk crystals. The mean size of VOPc nanoparticles was 17 +/- 7 nm, estimated by a scanning electron microscope (SEM) analysis.

DOI： 10.1246/cl.2004.724

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper is concerned with Rayleigh scattering spectroscopy using a dark-field optical microscope for the purpose of studying optical and electronic properties of isolated single nanoparticles. Size dependent optical resonance of organic nanocrystals was demonstrated using an optical microscope setup coupled with AFM. The adsorption effects of molecules on the surface plasmon resonance spectra of individual gold nanoparticles were examined in detail and the potential application of the single-nanoparticle SPR to chemical and biological sensors is discussed.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

DOI： 10.1016/S1574-0641(04)80008-1

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

DOI： 10.1016/S1574-0641(04)80019-6

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Language：Japanese  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

Intense excimer laser irradiation of vanadyl phthalocyanine (VOPc) microcrystals dispersed in poor solvents yields VOPc nanoparticles, which was confirmed to be common among some representative solvents. The mean diameters of the nanoparticles formed in water, methanol, ethanol, I-propanol, and ethyl acetate were determined to be 50 nm, 46 nm, 37 nm, 32 nm, and 38 nm, respectively. Absorption spectral analysis of the nanoparticles indicates that the VOPc nanoparticles from ethanol, I-propanol, and ethyl acetate exhibit stable phase H, while those from water exhibit phase I and those from methanol cannot be identified. To understand the solvent effect, we attempted to correlate the mean diameter and the absorption spectrum with various solvent parameters such as density, viscosity, thermal diffusivity, dipole moment, dielectric constant, and solubility. Experimentally, the thermal diffusivity of a solvent can be correlated with nanoparticle formation, which is considered in relation to the ablation mechanism.

DOI： 10.1143/JJAP.42.2725

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN CHEMICAL SOC  

Some new nanohybrid materials have been synthesized by intercalating the oxotitanium(IV) meso-tetrakis(4-sulfonatophenyl) porphyrin(O=Ti-(IV) TSPP) into the Zn/Al layered double hydroxides (LDHs), and their structures and photophysical properties have been investigated by various laser spectroscopic techniques. According to the XRD pattern of the synthesized nanohybrid materials, the macrocycle plane of O=Ti-(IV) TSPP are grafted perpendicular to the LDH layers. The O=Ti-(IV) TSPP-intercalated LDH exhibits band broadening of the absorption spectrum and a blue shift of Q-band as compared to that observed in solution. Resonance Raman spectral measurements demonstrate that the positively charged LDHs give rise to a slight decrease of the electronic density of the porphyrin ring accompanying a small change of the electronic distribution of the O=Ti-(IV) TSPP. Consequently the LDH environment affects the energies of the two highest occupied molecular orbitals (HOMOs) of the O=Ti-(IV) TSPP, a(1u) and a(2u), producing a mixed orbital character. Being consistent with these electronic structural changes of O=Ti-(IV) TSPP in LDH, both the fluorescence spectral change and the fs-diffuse reflectance transient measurements imply that the photoexcitation of the O=Ti-(IV) TSPP intercalated into LDH undergoes fast relaxation to the O=Ti-(IV) TSPP+-LDH- charge transfer (CT) state within a few picoseconds, followed by a photoinduced electron transfer between the O=Ti-(IV) TSPP and LDHs with a rate constant greater than I X 10(10)S(-1). No evidence is found for back electron transfer. In conclusion, the O=Ti-(IV) TSPP intercalated LDH seems to be a possible candidate for an artificial reaction center for an efficient solar energy conversion system.

DOI： 10.5012/bkcs.2003.24.4.446

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The spectroscopic properties of seven varieties of wire-type dendrimers, which consist of different generation numbers of dendritic wedges and molecular weights, were examined in tetrahydrofuran solution, in the solid state, and in good/poor solvent mixture for the purpose of revealing the relation between molecular conformation and spectral behavior. The second and third generation wire-type dendrimers showed a sharp aggregate band, which is ascribed to the interchain π stacked aggregate, in the solid state and in the good/poor solvent mixture, while the fourth generation wire-type dendrimer did not show the aggregate band. The absence of the aggregate band indicates that the bulky fourth generation dendritic wedges prevent the conjugated backbone from forming the interchain π stacked aggregate even in the solid state and in the good/poor solvent mixture. In the experiment on poor solvent-induced aggregation, we observed the progressive spectral change in the process of forming the aggregate, and simultaneously the aggregate formation was confirmed by observation of the fluorescence microscope image. The progressive spectral change suggested the molecular conformational change during the aggregate formation. Furthermore, the difference of molecular conformation depending on each aggregate and on some positions of the single aggregate was revealed using fluorescence microspectroscopy with the spatial resolution of about 1 μm.

DOI： 10.1021/jp021643z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The spectroscopic properties of seven varieties of wire-type dendrimers, which consist of different generation numbers of dendritic wedges and molecular weights, were examined in tetrahydrofuran solution, in the solid state, and in good/poor solvent mixture for the purpose of revealing the relation between molecular conformation and spectral behavior. The second and third generation wire-type dendrimers showed a sharp aggregate band, which is ascribed to the interchain pi stacked aggregate, in the solid state and in the good/poor solvent mixture, while the fourth generation wire-type dendrimer did not show the aggregate band. The absence of the aggregate band indicates that the bulky fourth generation dendritic wedges prevent the conjugated backbone from forming the interchain pi stacked aggregate even in the solid state and in the good/poor solvent mixture. In the experiment on poor solvent-induced aggregation, we observed the progressive spectral change in the process of forming the aggregate, and simultaneously the aggregate formation was confirmed by observation of the fluorescence microscope image. The progressive spectral change suggested the molecular conformational change during the aggregate formation. Furthermore, the difference of molecular conformation depending on each aggregate and on some positions of the single aggregate was revealed using fluorescence microspectroscopy with the spatial resolution of about 1 mum.

DOI： 10.1021/jp021643z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We investigated photoisomerization dynamics of spironaphthooxazine (SNO) and its chloro-substituted derivative (CI-SNO) in crystalline phase by femtosecond diffuse reflectance absorption spectroscopy. Although the photoinduced ring-opening reaction occurred in 3 ps and &lt;1 ps for SNO and Cl-SNO, respectively, photoisomerization to transplanar photomerocyanine did not take place. The generated non-planar open form of SNO lived for 2 ns, while that of Cl-SNO returned to the spiro form in I ps. The crystalline phase results are compared to the analogous experiments in amorphous solids with a view of restricted conformational changes of molecules embedded in a crystal lattice. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0009-2614(02)01867-5

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Language：Japanese   Publisher：シーエムシー出版  

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Femtosecond transient absorption spectroscopy was used to study how polyimide (PI) interacts with light in a nanometer-thick PI thin film. The PI containing pyromellitic diimide (PMDI) shows absorption by PMDI anions around 710 nm. Its decay occurs on two time scales: one is on the order of 10 ps and the other is on the order of a nanosecond. Each decay time is independent of the excitation wavelength and energy density, indicating that a geminate recombination would be dominant in a PI film. Under excitation by 390 nm light, the faster decay process shows one-photon absorption, but the slower decay process shows a two photon-absorption process.

DOI： 10.1021/jp013864v

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Fermosecond transient absorption spectroscopy was used to study how polyimide (PI) interacts with light in a nanometer-thick PI thin film. The PI containing pyromellitic diimide (PMDI) shows absorption by PMDI anions around 710 nm. Its decay occurs on two time scales: one is on the order of 10 ps and the other is on the order of a nanosecond. Each decay time is independent of the excitation wavelength and energy density, indicating that a geminate recombination would be dominant in a PI film. Under excitation by 390 nm light, the faster decay process shows one-photon absorption, but the slower decay process shows a two photon-absorption process.

DOI： 10.1021/jp013864v

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We report the first ultrafast ring closure kinetics of the merocyanine (MC) of a reverse photochromic spiropyran 1',3',3'-trimethyl-6,8-dinitrospiro[2H-1-benzopyran-2,2-indoline] (6,8-dinitro BIPS) and its 1'-(2-carboxyethyl) substituted derivative. The reaction is fast and essentially over in a few hundred picoseconds. The rate of MC-S-1 state decay evaluated from transient absorbance can be correlated directly with the MC-S-1 state lifetime as determined using stimulated and ordinary emission measurements. The recovery of the MC-S-0 state from MC-S-1 has a component with a lifetime of 60-78 ps in acetonitrile with a second component of 350-470 ps probably due to a metastable intermediate. We can further establish that the excited MC-S-1 state takes on the order of 500 fs to form from higher-energy states after photoexcitation with 390 nm light.

DOI： 10.1021/jp012564a

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Photochromism of indolinospironaphthooxazine (SNO) microcrystalline powder was investigated by steady state and time-resolved diffuse reflectance spectroscopy using a femtosecond laser as a light source. When laser intensity is weak, the photoinduced ring-opening reaction in a picosecond time region and subsequent thermal ring-closure one in a nanosecond scale take place in the crystal, not leading to permanent photocoloration of the powder. The same sample shows photochromism upon intense femtosecond laser excitation. The absorption spectra after laser excitation are similar to those of the photocolored form in solution. The spectral shape is independent of the laser fluence, whereas the yield increases nonlinearly with the fluence. To reveal the photocoloration mechanism, we examined the excitation fluence dependence of the transient absorption spectra and elucidated the photocoloration behavior by femtosecond double pulse excitation varying the delay of the two pulses. These experimental results show that cooperative interactions between the excited states and short-lived intermediates are important to generate a long-lived photomerocyanine. Femtosecond induced photocoloration will be discussed in terms of transient and local lattice deformations, and a cooperative photochemical reaction model is proposed.

DOI： 10.1021/jp0129838

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Excited-state dynamics of 9,9'-biantryl (BA) adsorbed on the porous glass, where the large motion of the surrounding medium or intramolecular motion of BA was not plausible, and temperature effects on it were investigated by means of steady-state fluorometry, absorption measurement, picosecond transient absorption spectroscopy, and time-resolved fluorescence measurement. Steady-state fluorescence and transient absorption spectroscopy revealed that the electronic structure of excited BA had strong charge transfer (CT) character as comparable as in the polar solutions both at room temperature and at 77 K, although the dielectric environments estimated by other inter- and intramolecular CT systems were in nonpolar or very weakly polar environments. The time constant of CT was determined to be 5-10 ps at 294 K. The CT time constant was slightly slower (ca. 20 ps) at 77 K but was much faster than that of BA in alcoholic solutions at room temperature. By integrating these results with those in solutions, the rapid CT state formation and the stabilization of the CT state were discussed from the viewpoint of the symmetry breaking in the ground state because of the heterogeneous adsorption of BA onto the glass surface.

DOI： 10.1021/jp012311h

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Water suspension of micrometer-sized vanadyl phthalocyanine (VOPc) crystals was converted into VOPc colloidal solution by irradiation with an excimer laser (351 nm, 30 ns, 5 Hz). VOPc nanoparticles with nearly equilateral triangular and hexagonal shapes were obtained from the colloidal solution, and the mean width and height are 60 and 19 nm for triangular nanoparticles, respectively, and 49 and 17 nm for hexagonal ones, respectively. Laser fluence dependence was examined and laser ablation of the microcrystals in water is considered to be responsible for the nanoparticle formation. A threshold laser fluence of the conversion was determined to be similar to20 mJ/cm(2). Nanoparticle formation processes and their phase transition during standing were analyzed by electronic absorption spectroscopy.

DOI： 10.1021/jp012518a

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Laser manipulation and laser trapping techniques were applied to μm sized gel-like wire-type dendrimer (L3PPE130 and L4PPE8) assemblies, which are formed at drying process of their tetrahydrofuran (THF) solution on a glass substrate. Deformation and extension of single gel-like assemblies were demonstrated with irradiation of a focused 1064 nm laser beam by scanning a microscope stage. In repetitive irradiation experiments, contraction and swelling of the gel-like assembly were observed in response to the switch on and off of the laser beam, respectively, and in the case of the L3PPE130 gel-like assembly, fluorescence spectra detected at a focal point changed accompanying the contraction and swelling behavior. This spectral change means molecular aggregates were formed transiently by photon pressure of the focused near-infrared laser beam.

DOI： 10.1021/jp013367e

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To test the influence of the surrounding medium on the relaxation dynamics of the plasmon band bleach recovery of gold nanoparticles after excitation with femtosecond laser pulses, we embedded 14.5 and 12.1 nm colloidal gold nanoparticles (synthesized electrochemically) in MgSO4 powder and investigated these samples by femtosecond diffuse reflectance spectroscopy. By measuring the relaxation dynamics over a wide range of excitation energies, we found that the fast decay component is slower by about a factor of 2 for the particles in the MgSO4 powder compared to those in solution while no significant change in the slow decay component is observed. In agreement with this observation, we found that adding solvent to the particles embedded in the powder caused a decrease in the relaxation time from about 10 ps to 5 ps for the fast decay component. This leads to the conclusion that the electron-phonon relaxation in these gold nanoparticles depends on the chemical nature and/or physical phase (solid vs solution) of the surrounding medium. A discussion of this in terms of the type of phonon involved, and the nature of the electron-phonon and phonon-phonon relaxation processes is discussed. To our knowledge, this also presents the first time that a transient bleach could be observed by diffuse reflectance spectroscopy.

DOI： 10.1021/jp013311k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Laser manipulation and laser trapping techniques were applied to mum sized gel-like wire-type dendrimer (L3PPE130 and L4PPE8) assemblies, which are formed at drying process of their tetrahydrofuran (THF) solution on a glass substrate. Deformation and extension of single gel-like assemblies were demonstrated with irradiation of a focused 1064 nm laser beam by scanning a microscope stage. In repetitive irradiation experiments, contraction and swelling of the gel-like assembly were observed in response to the switch on and off of the laser beam, respectively, and in the case of the L3PPE130 gel-like assembly, fluorescence spectra detected at a focal point changed accompanying the contraction and swelling behavior. This spectral change means molecular aggregates were formed transiently by photon pressure of the focused near-infrared laser beam.

DOI： 10.1021/jp013367e

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To test the influence of the surrounding medium on the relaxation dynamics of the plasmon band bleach recovery of gold nanoparticles after excitation with femtosecond laser pulses, we embedded 14.5 and 12.1 nm colloidal gold nanoparticles (synthesized electrochemically) in MgSO4 powder and investigated these samples by femtosecond diffuse reflectance spectroscopy. By measuring the relaxation dynamics over a wide range of excitation energies, we found that the fast decay component is slower by about a factor of 2 for the particles in the MgSO4 powder compared to those in solution while no significant change in the slow decay component is observed. In agreement with this observation, we found that adding solvent to the particles embedded in the powder caused a decrease in the relaxation time from about 10 ps to 5 ps for the fast decay component. This leads to the conclusion that the electron-phonon relaxation in these gold nanoparticles depends on the chemical nature and/or physical phase (solid vs solution) of the surrounding medium. A discussion of this in terms of the type of phonon involved, and the nature of the electron-phonon and phonon-phonon relaxation processes is discussed. To our knowledge, this also presents the first time that a transient bleach could be observed by diffuse reflectance spectroscopy.

DOI： 10.1021/jp013311k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We investigated single gold nanoparticles embedded in poly(vinyl alcohol) (PVA) films with different thicknesses using Rayleigh light-scattering microspectroscopy. First, gold nanoparticles with a mean radius of 40 nm were dispersed in a thin polymer film. Then, the film was covered with multiple layers of PVA to the desired thickness. As a result, we confirmed that the surface plasmon (SP) resonance band of single particles demonstrated redshift with the film thickness increase. In a thick film, the SP band peak position was well explained in terms of the size of Lite gold nanoparticles. In contrast, the spectral variance observed in a thin film did not follow the size-dependence trend. Since nanoparticles in a thin film are partially covered with PVA layers and thus are partially exposed to air, our results confirm that SP resonance strongly depends not only on a Particle's size but also on its surrounding dielectric conditions.

DOI： 10.1143/JJAP.41.L76

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Laser ablation transfer of phthalocyanine dyes to neat poly(methyl methacrylate) (PMMA) film was achieved space-selectively by femtosecond laser excitation. The transferred pattern at the laser fluence near ablation threshold was a dot with a diameter of a few micrometers, and a bigger doughnut pattern was obtained at higher fluence. By measuring the absorption spectra of original and deposited dyes, their crystal phase was confirmed to change upon femtosecond laser transfer depending on laser fluence. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0169-4332(02)00413-0

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Photocoloration of microcrystalline powder of spirooxazine and spiropyran compounds induced by femtosecond laser excitation was investigated using time-resolved and steady state diffuse reflectance spectroscopy. The intermediate products were observed in a ns time region, and assigned to non-planar open forms. On the other hand, photocoloration can occur even in the crystalline phase by intense femtosecond pulse excitation, and the yield of colored forms increased nonlinearly with laser fluence. The mechanism of photochromic reaction induced by high-density excitation is discussed on the basis of excitation fluence and shot number dependences of photocoloration, thermal bleaching of colored forms, and transient absorption spectra. It is considered that free volume around molecules to change the molecular conformation is generated due to the local deformed crystal lattice following the densely formed excited states and intermediate products.

DOI： 10.1039/b108108j

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Time-resolved interferometry, surface light scattering imaging, and optical microscopic imaging have been developed and applied to amorphous and multicrystalline films upon intense pulsed excitation. Nanosecond interferometry of neat polystyrene film gives interesting expansion dynamics followed by complete recovery. Femtosecond surface light scattering imaging reveals the roughing processes of Copper phthalocyanine (CuPc) films. Femtosecond optical microscopic imaging of a single anthracene microcrystal shows dynamics of its laser-induced fracture and destruction. All the morphological behaviors have been directly measured in the time domain by these newly developed pump-probe methods. Ablation of CuPc crystalline and amorphous films show novel dependence of etch profile on excitation pulse width; fs etch depth increases stepwise with laser fluence, while ns etch depth becomes gradually deep as fluence does. The results are discussed in view of how electronic excitation energy evolves to morphological change.

DOI： 10.1117/12.456806

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SOC CHEMICAL ENG JAPAN  

Gold nanoparticles were prepared by the reduction of sodium tetrachloroaurate in water-in-oil microemulsion, by using polyoxyethylene dodecyl ether, bis 2 ethylhexyl sodium sulfosuccinate, or didodecyl dimethyl ammonium bromide as a surfactant. When the molar ratio of water to surfactant became small, the size of microemulsion was almost monodispersed, and nanoparticles were produced and dispersed well in microemulsion solution. Furthermore, monodispersed nanoparticles were obtained when the number of gold ions per water droplet in microemulsions was above one. The diameter of gold nanoparticles was controllable by the average size of microemulsion. By use of a strong reducing agent such as hydrazine or sodium borohydride, small gold particles could be made.

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Novel laser etching was demonstrated by one-shot femtosecond laser ablation of a transparent organic amorphous film. The etch depth increased stepwise with increasing laser fluence and each step is constant and independent of the fluence, while the number of steps and etching area increase with the fluence. The successive depths were 270, 480, 690 and 820 nm, for which the thresholds were 180, 180, 210 and 290 mJ/cm(2), respectively. A fifth step was not observed in the present fluence range. Both the etched surfaces and slopes between the steps are very smooth with a roughness of less than 10 nm. The mechanism is proposed and discussed in view of the optical interference effect and a possible application is mentioned.

DOI： 10.1143/JJAP.40.L1116

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Language：Japanese   Publisher：The Laser Society of Japan  

A novel femtosecond laser etching and its mechanism of Cu-phthalocyanine solid were investigated by using fs (170 fs) and ns (100 ns) pulses of a 780 nm Ti: Sapphire laser. Above ablation thresholds, the depth etched by fs laser excitation becomes constant and is almost independent of laser fluence, while the depth etched by ns laser excitation increases gradually. We name the unique fs ablation phenomenon "discrete etching". In order to reveal the evolutions from fs laser excitation to the nm etching, we measured directly excitation energy relaxation and surface morphology change with fs transient absorption spectroscopy and fs surface light scattering imaging, respectively. On the basis of the results, we propose a fs laser ablation model that ultrafast stress increase brings about mechanical disruption leading to the discrete etching behavior.

DOI： 10.2184/lsj.29.710

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Laser ablation and etching of microcrystalline Cu-phthalocyanine thin films were examined by changing pulse duration (170 fs, 250 ps, 100 ns) of a 780 nm Ti:sapphire laser. Above fs (40 mJ/cm(2)) and ps (50 mJ/cm(2)) ablation thresholds, the etch depth becomes constant and is almost independent of laser fluence, and further increase in the fs fluence results in complete removal of the film. We name the unique ablation phenomenon discrete etching. On the other hand, the depth etched by ns laser excitation increases gradually with the fluence above its ablation threshold (80 mJ/cm(2)). In order to reveal the difference between the fs and ns etching behaviors, we measured directly excitation energy relaxation and surface morphology change with time-resolved absorption spectroscopy and time-resolved surface scattering imaging, respectively. The fs discrete etching phenomenon and its mechanism were considered in view of time evolutions from highly intense fs laser excitation to the step-wise etching. On the basis of the results, we propose a fs laser ablation model that ultrafast stress increase brings about mechanical disruption leading to the discrete etching behavior.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Nanosecond 351 nm excimer laser irradiation of microcrystalline powders of aromatic hydrocarbons and phthalocyanine (Pc) dyes in water results in conversion from opaque suspensions to transparent colloidal solutions. Formation of similar to 100 nm-sized particles an successfully confirmed for oxo(phthalocyaninato)vanadium(IV) (VOPc) by AFM observation. The particles in solution are stable, while some Pc colloid solutions show interesting slow UV absorption spectral changes, which is interpreted in terms of phase transition. It is discussed that the present laser ablation of solution is regarded not only as a new nanoparticle formation method but also as a control way of molecular aggregation in nanoparticles. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0169-4332(00)00596-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOHN WILEY & SONS LTD  

Fluorescence decay curves of single fluorescent polysryrene beads in poly(vinyl alcohol) (PVA) films are measured with a confocal microscope, and quenching dynamics of the single beans by adsorbed methylene blue (MB) is examined. The fluorescence lifetimes oft he beads are identical, while the quenching efficiency differs from bead to bend. This is related with inhomogeneity of adsorbed MB on the beads in PVA films, Nonexponential fluorescence decays of single beans with MB confirm that fluorophores near the bend surface are quenched by adsorbed quencher while the inner part of the bend is not affected. The importance of single bean florescence measurement is discussed. Copyright (C) 2000 John Wiley & Sons, Ltd.

DOI： 10.1002/1099-1581(200008/12)11:8/12<772::AID-PAT27>3.0.CO;2-S

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Language：English   Publisher：The Chemical Society of Japan  

A series of covalently linked porphyrin-quinone molecules in which a porphyrin ring is connected at two fixed distances with two different kinds of rigid spacers to benzoquinone were synthesized. The spacer is either spiro[4.4]nonane or <i>trans</i>-decalin. These compounds were designed to have a fixed orientation of different kinds with the same redox pair, the same separation distance, and the same number of intervening bonds. The forward electron-transfer rates were studied by fluorescence–lifetime measurements. Large differences in the rates were found in each pair, and the rates for those compounds having a spiro spacer were larger than those with a <i>trans</i>-decalin spacer. These differences were attributed to a difference in the molecular geometry of the spacer groups in each pair.

DOI： 10.1246/bcsj.67.3067

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE PUBL B V  

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In order to understand the mutual orientation effect in photosynthetic electron transfer, two different kinds of quinone-linked porphyrins 1 and 2 with fixed orientation were synthesized. In the two compounds only orientation is different among various factors which control electron transfer. It has been found that the electron transfer of 1 is faster than 2 by a factor of nine.

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Characteristic absorption of the anion radical of pyromellitimide around 715 nm was demonstrated to be particularly useful for studies on photoinduced electron transfer reactions. Charge recombination in pyromellitimide-linked porphyrin was greatly retarded in benzene due to the large energy gap and small reorganization energy. A long-lived charge separated state (tau = 2.5-mu-s) was formed in the case of a diporphyrin-porphyrin-pyromellitimide triad system.

DOI： 10.1246/cl.1991.1003

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5,10,15,20-Tetraphenyl-21H,23H-porphine manganese(III) chloride ((MnTPP)-T-III(Cl)) was encapsulated into MCM-41 and TiMCM-41, and its photoinduced electron transfer had been studied by using femtosecond diffuse reflectance photolysis. Two different transient species (c.a. 10 ps and c.a. 80 ps) were observed. The shorter-lived species should be originated from relaxation of a "tripmultiplet" state and the longer-lived species should be attributed to the spin-forbidden relaxation (slower than the spin-allowed decay of triptquintet) via a quintet CT state. After irradiation, MnTPPCI+. radicals are detected in MCM-41 or TiMCM-41, indicating that the mesoporous silicate framework plays a good electron acceptor. Furthermore, it has been found that the formation MnTPPCI+. is easier in TiMCM-41 than in MCM-41, indicating that framework modification by incorporating the Ti4+ into the MCM-41 enhances the electron-accepting ability of the MCM-41 framework.

DOI： 10.1021/jp0116757

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We have developed an ultrafast, light-scattering spectroscopic system combining a conventional microscope with a pump-probe setup. We successfully measured the surface plasmon resonance band for the individual gold particles with a mean radius of 40 nm. The results on the pump-probe experiment demonstrate that both the electron-phonon and the phonon-phonon coupling processes in the individual gold particles take place with the lifetimes of 4 ps and &gt; 25 ps, respectively. (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1402962

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Novel etching of Cu-phthalocyanine (CuPc) amorphous film which is characteristic of ultrashort laser irradiation was successfully confirmed by tuning Ti:Sapphire laser (780 nm) to 150 fs, 250 ps, or 100 ns, and the primary processes were investigated by fs pump-fs probe and ps pump-fs probe spectroscopic measurements. In the fs and ps laser ablation, we have found discrete laser etching in that the etch depth becomes constant and is independent of laser fluence above the ablation threshold, although gradual (normal) etching, in which the etch depth increase continuously with the fluence above ablation threshold, was observed in the ns laser ablation. The transient absorption spectral measurements reveal the nonlinear photothermal conversion processes, corresponding to exciton-exciton annihilation and cyclic multiphotonic absorption. Their time evolutions during and after the excitation pulse duration were considered and elucidated to depend strongly on the excitation pulse width. On the basis of these results, we discuss an ablation mechanism for the ps and fs ablation that the temperature elevation bringing about transient high pressure is responsible for discrete etching. (C) 2001 Published by Elsevier Science B.V.

DOI： 10.1016/S1010-6030(01)00514-7

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The primary photochemical event of photoactive yellow protein (PYP) was studied by laser flash photolysis experiments on a subpicosecond-nanosecond time scale. PYP was excited by a 390-nm pulse, and the transient difference absorption spectra were recorded by a multichannel spectrometer for a more reliable spectral analysis than previously possible. Just after excitation, an absorbance decrease due to the stimulated emission at 500 nm and photoconversion of PYP at 450 nm were observed. The stimulated emission gradually shifted to 520 nm and was retained up to 4 ps. Then, the formation of a red-shifted intermediate with a broad absorption spectrum was observed from 20 ps to 1 ns. Another red-shifted intermediate with a narrow absorption spectrum was formed after 2 ns and was stable for at least 5 ns. The latter is therefore believed to correspond to I1 (PYPL), which has been detected on a nanosecond time scale or trapped at -80 degreesC. Singular value decomposition analysis demonstrated that the spectral shifts observed from 0.5 ps to 5 ns could be explained by two-component decay of excited state(s) and conversion from PYPB to PYPL. The amount of PYPL at 5 ns was less than that of photoconverted PYP, suggesting the formation of another intermediate, PYPH. In addition, the absorption spectra of these intermediates were calculated based on the proposed reaction scheme. Together, these results indicate that the photocycle of PYP at room temperature has a branched pathway in the early stage and is essentially similar to that observed under low-temperature spectroscopy.

DOI： 10.1021/bi002437p

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：AMER CHEMICAL SOC  

The self-assembled structures by evaporation of tetrahydrofuran (THF) solution of wire-type dendrimers have been studied by some spectroscopic and microscopic techniques. Doughnut-like structures were obtained for some dendrimers with generation number of 2 and about 28 nm length by depositions their THF solutions on a quartz substrate, while yam-like and particle-like structures were obtained for other dendrimers. The size of the doughnut structure Varied from I to 8 mum in diameter and between 30 and 150 nm in height. Confocal fluorescence microscopy, atomic force microscopy (AFM), and near-field scanning optical microscopy (NSOM) were applied to elucidate assembled structures and electronic properties in addition to conventional fluorescence spectroscopy. Polarization and local fluorescence measurements at some parts of doughnuts and particles were demonstrated, however, no correlation between molecular orientation/intermolecular interaction and doughnut structures was found. The doughnut formation mechanism is considered on the basis of evaporation processes observed from in situ experiments.

DOI： 10.1021/jp0040594

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Transient absorption spectra of Pt-loaded TiO2 powder photocatalysts were measured by femtosecond diffuse reflectance spectroscopy and the dynamics of photogenerated electrons in TiO2 were investigated. The Pt-loaded TiO2 showed a new decay component of a few ps under 390 nm excitation in addition of normal charge recombination kinetics. This fast decay process can be interpreted as migration of electrons in TiO2 to Pt on the basis of detailed measurements changing experimental conditions such as Pt-loading, excitation wavelength and excitation fluence. These results clearly indicate that charge separation is responsible for the well-known enhancement of the catalytic reactivity of Pt-loaded TiO2. (C) 2001 Published by Elsevier Science B.V.

DOI： 10.1016/S0009-2614(01)00128-2

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：SPRINGER  

On the basis of transient absorption spectral measurements in the whole visible region using femtosecond diffuse reflectance spectroscopy, a hole transfer process from photoexcited TiO2 to an adsorbed molecule SCN- was elucidated. In a TiO2 aqueous suspension with KSCN. absorption rise of dimer radical anion (SCN)(2)(.-) was observed indicating hole transfer. Interestingly, there were two rise components with &lt;1 ps and several 100 ps, which were shorter in lower pH of the solution. Ultrafast hole transfer and subsequent intermolecular geometrical change of a dimmer radical anion are also discussed.

DOI： 10.1163/156856701745069

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DOI： 10.1016/S0272-8842(00)00039-0

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Fluorescence decay curves of single fluorescent polysryrene beads in poly(vinyl alcohol) (PVA) films are measured with a confocal microscope, and quenching dynamics of the single beans by adsorbed methylene blue (MB) is examined. The fluorescence lifetimes oft he beads are identical, while the quenching efficiency differs from bead to bend. This is related with inhomogeneity of adsorbed MB on the beads in PVA films, Nonexponential fluorescence decays of single beans with MB confirm that fluorophores near the bend surface are quenched by adsorbed quencher while the inner part of the bend is not affected. The importance of single bean florescence measurement is discussed. Copyright (C) 2000 John Wiley & Sons, Ltd.

DOI： 10.1002/1099-1581(200008/12)11:8/12<772::AID-PAT27>3.0.CO;2-S

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Absorption and fluorescence spectra of 4-n-pentyl-4"-cyano-p-terphenyl (5CT) films deposited on hydrophilic and hydrophobic quartz substrates were measured and compared with those of its various solutions and of its neat forms (crystalline, liquid crystal, and isotropic phases). Further, these spectra were compared with those of 4-n-alkoxy-4'-cyanobiphenyls (nOCB, n = 8, 9, 10, 12), which had been studied in detail already. The absorption and fluorescence spectra of the 5CT-deposited films were almost independent of substrate property and deposition temperature. This behavior was different from those observed for nOCB. The absorption spectra differed from those of its solution samples and suggested that cyanoterphenyl groups of 5CT molecules in the deposited films form H-aggregate-like structures with their long axes parallel to each other and relatively perpendicular to the stacking direction in the deposited films. The fluorescence spectra were also different from those of its neat and solution samples. Surface morphology of the deposited films was also investigated using atomic force microscopy (AFM), AFM images showed that the deposited films consisted of a number of small plate crystals, which was consistent with H-aggregate-like structures of cyanoterphenyl groups, and that The small plate crystals transformed to needle ones with time. The structural transformation correlated with the absorption and fluorescence spectral changes with time. The deposition processes of 5CT as revealed by in situ fluorescence spectra during deposition were simple compared with those of nOCB and are discussed on the basis of the in situ fluorescence spectra and the AFM images. (C) 2000 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0040-6090(00)00933-0

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Femtosecond laser ablation dynamics of an amorphous thin film of a substituted Cu-phthalocyanine was studied using time-resolved absorption spectroscopic and scattering imaging methods. Above the ablation threshold of 45 mJ/cm(2), the etch-depth is about 400 nm and almost constant up to a laser fluence of 300 mJ/cm(2). Transient absorption spectra confirmed that the electronic excitation energy is converted to heat through exciton-exciton annihilation within 100 ps after excitation. The etching profile and ablation threshold are discussed in connection with the heating rate. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0169-4332(99)00484-5

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Language：Japanese   Publisher：The Laser Society of Japan  

DOI： 10.2184/lsj.28.314

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Language：Japanese   Publisher：The Laser Society of Japan  

DOI： 10.2184/lsj.28.374

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Language：Japanese   Publisher：The Laser Society of Japan  

DOI： 10.2184/lsj.28.450

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Language：English   Publisher：GORDON BREACH SCI PUBL LTD  

Transient absorption spectra of 1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-(2H)-indole] (6-nitro-BIPS) microcrystalline powder were measured by femtosecond diffuse reflectance spectroscopy and compared with those in the benzene solution and in a PMMA film. A very similar photochromic reaction occurs even in the crystal, although the structure of the generated photo-colored form in crystalline phase is not as planar as that of a stable form (trans-planar merocyanine) in solution. Photocoloration and the following thermal back reaction dynamics are considered in terms of free volume of the matrix and limited motion of the molecule.

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Dynamics of charge carriers generated by femtosecond UV (160 fs, 390 nm) excitation in five standard TiO 2 photocatalytic powders (JRC-TIO-1, -2, -3, -4, and -5 supplied by the Catalysis Society of Japan) in a vacuum and air was investigated by means of time-resolved femtosecond diffuse reflectance spectroscopy, and was discussed from the viewpoints of crystal structure (anatase and rutile), particle size, and surrounding condition around the particles. Anatase TiO 2 catalysts showed very rapid (less than ps) and very slow electron-hole recombination processes, while rutile ones did not show any rapid decay. For catalysts composed of small particles, slower electron-hole recombination was observed in air compared with that in a vacuum, which was well explained in terms of upward band bending near the surface due to adsorption of oxygen. The relationship between the observed charge carrier dynamics and photocatalytic reactivity is also discussed. © 1999 American Chemical Society.

DOI： 10.1021/jp984162h

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Language：English   Publisher：AMER CHEMICAL SOC  

A time-resolved absorption spectroscopic measurement of liquid toluene under femtosecond UV (300-500 fs, 248 nm) laser ablation conditions was carried out, and its molecular mechanism was studied. The lowest excited singlet state of toluene monomer and toluene excimer were clearly observed through the delay time by 19 ns, while benzyl radical was not detected unexpectedly under any condition no matter how high the laser fluence was. This indicates that the femtosecond laser ablation is based on a photothermal mechanism. A femtosecond double-pulse excitation, on the other hand, induced benzyl radical formation, which is consistent with the photochemical mechanism in the case of nanosecond laser ablation. The result that molecular mechanism is dependent on the excitation laser pulse width suggests a possible mechanism control of laser ablation.

DOI： 10.1021/jp992565r

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Language：English   Publisher：INST PURE APPLIED PHYSICS  

Propagation of a femtosecond white-light continuum pulse (350 fs) in poly (methyl methacrylate) (PMMA) latex powders with particle diameters of 1, 5, 20, 60, and 100 mu m was investigated by means of an optical Kerr gate and time-resolved diffuse reflectance spectroscopy, which is a pump-probe technique for multiple light scattering materials. The temporal profile of a diffuse reflected light pulse from the powder and the temporal response of transient absorption of the powder doped with an organic molecule were measured. The Kubelka-Munk model was extended to address the propagation of a short light pulse, and its numerical simulations reproduced both experimental results quite well. It is suggested that in a dense scattering medium such as powder, an effect that light is confined or proceeds in a twisted manner is of importance. Fitting the experimental data with the diffusion theory was unsuccessful, which is also discussed.

DOI： 10.1143/JJAP.38.4236

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Language：English   Publisher：CHEMICAL SOC JAPAN  

A femtosecond regular reflection spectroscopic system was developed and applied to a P-copper phthalocyanine (beta-CuPc) pellet. Transient regular reflection spectra were converted into extinction coefficient change (Delta k) ones, which correspond to transient absorption spectra, by using Kramers-Kronig transformation. The Delta k spectrum observed immediately after excitation was assigned to the excited state of beta-CuPc solid, which relaxed by an exciton-exciton annihilation. The spectra remaining over several nanoseconds were assigned to a hot band due to a vibrationally excited state of the electronically ground state. We have clarified that a fast photothermal conversion process is induced by the exciton-exciton annihilation, which was analyzed by a simulation using a time dependent rate (proportional to t(-1/2)) of the annihilation.

DOI： 10.1246/bcsj.72.909

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Language：English   Publisher：AMER CHEMICAL SOC  

Charge-transfer (CT) complexes of 1,2,4,5-tetracyanobenzene (TCNB) with arene donor molecules were assembled within the supercages of faujasite zeolites with a two-step adsorption technique from solutions, and the transient absorption characteristics as well as the absorption and emission properties of these complexes were investigated. Several observations were made relevant to these neutral-type CT complexes which are adsorbed with a weak electronic interaction into zeolites rather than the Coulombic attraction which is predominant for the binding of CT complexes of pyridinium accepters previously studied: (1) the peak position of the CT bands suffers an appreciable shift depending on the chemical nature of the zeolites, (2) the apparent equilibrium constant for the complex formation depends both on the chemical nature of the zeolites and on the arene donors, (3) an appreciable effect of coadsorbed water, which has stronger interaction with the zeolite frameworks than the guest species, on the complex formation is noted, and (4) the relaxation process of the excited CT complexes is significantly retarded (at least 10 times) in dehydrated zeolites compared with that in polar solutions. These points were discussed on a qualitative basis because of the complexity of the systems. The CT complexes of TCNB with arene donors were found to be sensitive to the chemical properties of zeolites while those of pyridinium accepters with arenes have been reported to be sensitive to the physical properties such as the shape of cages as well as the size of entry apertures of zeolites.

DOI： 10.1021/la981496p

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Language：English   Publisher：ELSEVIER SCIENCE BV  

A time-resolved absorption spectroscopy system with an intense femtosecond KrF laser has been constructed and applied to liquid benzyl chloride under conditions of laser ablation. It has been directly confirmed over a wide fluence range that benzyl radical was formed immediately after excitation. In addition to the decay of benzyl radical, scattering of a probe light pulse was observed after similar to 1-2 ns at higher fluences, which was ascribed to morphological changes; the threshold was determined to be 30 mJ cm(-2). The femtosecond KrF laser ablation molecular dynamics of liquid benzyl chloride is well explained in terms of a photochemical mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0009-2614(98)01438-9

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Language：Japanese   Publisher：The Spectroscopical Society of Japan  

Femtosecond diffuse reflectance spectroscopy for studying ultrafast photophysical and photochemical processes of optically scattering materials has been developed and applied to photocatalytic TiO<SUB>2</SUB> powders. It is demonstrated that the spectroscopy has the similar spectroscopic and temporal resolutions to those of transmittance mode transient absorption one. Temporal behavior of diffuse reflected light is analysed by extended Kubelka-Munk model and simulated numerically. Excitation energy relaxation processes of TiO<SUB>2</SUB> powders are measured directly in femtosecond to nanosecond time domains, and electron-hole charge separa-tion and recombination dynamics, and charge transfer to adsorbed molecules on TiO<SUB>2</SUB> surface are made clear. The results are discussed in terms of physical and structural properties of TiO<SUB>2</SUB> and environmental conditions.

DOI： 10.5111/bunkou.48.143

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Language：English   Publisher：AMER INST PHYSICS  

Time-resolved surface scattering imaging was performed for liquid benzyl chloride and liquid toluene under femtosecond KrF laser ablation conditions. No scattering image was obtained until 1 ns, while scattering started from 2 ns when the laser fluence exceeded 25 mJ/cm(2), and its intensity increased with the passage of time. The higher the laser fluence was, the steeper the increasing slope was. The scattering is due to surface roughness, which is the initial stage of macroscopic morphological changes. Root-mean-square surface roughness was estimated from the scattering intensity by using frosted fused-silica plates as reference samples. The induced surface roughness increases to a few hundred nm in 10 ns. (C) 1998 American Institute of Physics. [S0003-6951(98)02150-0].

DOI： 10.1063/1.122816

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Language：English   Publisher：AMER CHEMICAL SOC  

Anthracene adsorbed into NaY and NaX zeolites has been investigated mainly with a fluorescence spectroscopic technique as a function of sample loading both in the absence and in the presence of various amounts of coadsorbates. At low loadings, emission spectra characteristic of anthracene monomer were observed in dehydrated zeolites with a small red-shift and an appreciable broadening in the vibrational structure compared to those in solutions and siliceous Y (USY) zeolite. The distorted spectra are indicative of the interaction between anthracene and the zeolite frameworks, namely Nai ions; the fluorescence spectroscopic detection of the interaction, the cation-pi interaction in zeolites, is made for the first time. As the loading level increases, a broad and structureless band ascribable to the excimer of anthracene was detected at the expense of the monomer emission bands. The dimers formed inside the supercages are responsible for the occurrence of the excimer emission, and the anthracene dimer is unique to the zeolites NaY and NaX. In hydrated zeolites, on the other hand, the monomer emission spectrum gave narrow vibronic bands. This observation reinforces the assignment of the broadening of the monomer emission bands to the Na+-anthracene interaction because water possesses larger affinity toward the zeolite frameworks than does anthracene and can act to reduce the cation-pi interaction by the screening effect. The contribution of excimer emission decreases in the presence of water and other coadsorbed solvents (methanol, acetonitrile). Furthermore, the formation of anthracene crystals was observed in the presence of a large amount of coadsorbed water, methanol, or acetonitrile. The crystals are suggested to be formed at the outer surfaces of zeolites through the process in which anthracene molecules are replaced by the solvents preferentially penetrating into the zeolite cavities. Dramatic changes in the adsorption state and association behavior of anthracene in zeolites were observed depending both on the loading level of anthracene and on the amount of coadsorbed water and other solvents.

DOI： 10.1021/la980311b

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Language：English   Publisher：CHEMICAL SOC JAPAN  

The electronic structure of the excited states and triplet formation dynamics in the acridine microcrystal have been studied by femtosecond diffuse reflectance absorption spectroscopy and picosecond fluorescence spectroscopy. It was confirmed that an excimer was formed in the microcrystal within a few picoseconds after excitation. The time constant of triplet formation from the lowest excited singlet (S-1) state was obtained to be about 900 ps at room temperature, which is about ten times slower than that in an aprotic solvent. Also, triplet formation was not observed up to 6 ns at 77 K. Slow intersystem crossing in the crystal was explained in terms of a selective stabilization of the (1)pi pi* electronic configuration due to excimer formation. An important role of intermolecular interactions on the intersystem crossing process of the crystal is discussed.

DOI： 10.1246/bcsj.71.1277

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Language：English   Publisher：AMER INST PHYSICS  

An ultrafast time-resolved diffuse reflectance spectroscopic system has been developed as a potential instrument for analyzing photophysical and photochemical dynamics of light scattering materials such as powder and opaque suspension, using an amplified femtosecond Ti:sapphire laser as a light source. Transient absorption spectra of organic powder, covering the wavelength region from 400 to 760 nm, were precisely obtained by using a stable and bright femtosecond white-light continuum as a probe light. An ultrashort light pulse is temporally broadened owing to numerous times of refraction, reflection, and diffraction in scattering materials. This affects the temporal resolution of transient absorption measurements, which was examined and discussed in detail by using a simple numerical model with time-dependent light propagation of a short pulse. From the simulation and experimental results, it was shown that the temporal resolution of transient absorption measurement is less than a few ps under a certain measurement condition, although it strongly depends on the optical properties of the sample; scattering and absorption coefficients. Some applications to the analysis of excited dynamics of organic molecules in polymer latex and molecular microcrystalline powder are also demonstrated. (C) 1998 American Institute of Physics.

DOI： 10.1063/1.1148668

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Language：English   Publisher：AMER CHEMICAL SOC  

Relaxation dynamics from a higher triplet excited state in alpha-sexithienyl (hereafter abbreviated as 6T) film was investigated by double-pulse excitation spectroscopy. Very rapid formation (within 1 ps) of the lowest singlet excited state and an intermolecular ion-pair state were observed. The mechanism of this rapid conversion process from a higher electronic excited state was discussed.

DOI： 10.1021/jp9733476

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Language：English   Publisher：GORDON BREACH PUBLISHING, TAYLOR & FRANCIS GROUP  

Femtosecond transient absorption spectral measurements have been performed for size-controlled polydiacetylene microcrystals (30, 100, and 150 nm mean diameter) dispersed in water. Ultrafast relaxation processes within 5 ps after excitation were attributed to formation and decay of self-trapped exciton, which was independent on the size. A time-dependent spectral shift of transient bleaching, corresponding to the stationary excitonic absorption band, was observed in the time region from 10 ps to a few ns. It is explained as a thermalization of absorbed light energy within the microcrystal and the succeeding cooling by comparing transient absorption spectra with temperature difference spectra of the ground state absorption. Size-dependent cooling dynamics of a &apos;hot&apos; microcrystal was successfully demonstrated; the time constant increases with the crystal size.

DOI： 10.1080/10587259808042462

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Language：English   Publisher：GORDON BREACH PUBLISHING, TAYLOR & FRANCIS GROUP  

Relaxation dynamics of photoexcited states in ultrathin multilayered films composed of copper phthalocyanine (CuPc) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), were investigated by femtosecond absorption spectroscopy. Absorption bands due to an electronically excited state and a vibrationally excited state of electronically ground state of CuPc were measured for the excitation at 390 nm 780 nm. Futhermore, an additional absorption band was observed when excited at 390 nm, which was assigned to an NTCDA excited state. Ultrafast energy transfer from NTCDA to CuPc takes place with the time scale of 1 ps at the interface between NTCDA and CuPc layers.

DOI： 10.1080/10587259808042456

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Language：English   Publisher：ELSEVIER SCIENCE SA  

Absorption and fluorescence spectra of 4-dodecyloxy-4'-cyanobiphenyl (12OCB) films deposited on hydrophilic and hydrophobic substrates were measured and compared with those of its neat form (crystalline, liquid crystal, and isotropic phases). Further, these spectra were compared with those of 4-octyloxy-4'-cyanobiphenyl (8OCB). In addition, surface morphology of the deposited films was investigated using atomic force microscopy (AFM). The absorption and fluorescence spectra of the deposited films were almost independent of substrate property and deposition temperature, which was different from the result of 8OCB. The absorption spectra of the 12OCB-deposited films were observed at short wavelengths compared with those of 12OCB in solution and the first band split into two bands, suggesting the formation of K-aggregate structures of cyanobiphenylyloxy groups in the deposited films. The fluorescence spectra of the deposited films were observed in the shorter wavelength region than those of its neat and solution samples and were never reported for other cyanobiphenyl-type liquid crystal compounds. This new fluorescence was responsible for the H-aggregate structures of the 12OCB-deposited films. AFM images showed that the deposited films consisted of a number of small plate crystals. The small plate crystals were considered to have smectic-like structure composed of bilayers, which was consistent with H-aggregate structures of cyanobiphenylyloxy groups suggested from the absorption and fluorescence spectra. The deposition processes of 12OCB were investigated by measuring in-situ fluorescence spectra during deposition and discussed in comparison with those of 8OCB. (C) 1997 Elsevier Science S.A.

DOI： 10.1016/S0040-6090(97)00696-2

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Language：English   Publisher：ROYAL SOC CHEMISTRY  

A yellow crystal 3 and a red crystal 4 simultaneously crystallize from a solution of acridine 1 and phenothiazine 2 in acetonitrile. Similar N ... H-N hydrogen bonding pairs of 1 and 2 are formed in the two crystals. The 3:4 crystal 3 has a slightly uncommon molecular arrangement of which four acridine molecules out of twelve are disordered in the unit cell. The 1:1 crystal 4 has a more rigid packing of the hydrogen bonding pairs, Irradiation of 3 gives a photoadduct 5 as the sole product, whereas 4 shows almost no photoreactivity. The occurrence of photoinduced electron transfer has been confirmed by the measurement of transient absorption spectra of the crystals 3 and 4. However, the two-stage decay of the transient absorption of 3 with lifetimes of 2 and 50 ps is different from that of 4 with a single short lifetime of 2 ps. Upon irradiating 3, electron transfer, proton transfer and subsequent radical coupling occur over the shortest distance of 4.1 Angstrom between the preradical carbon and nitrogen atoms in the crystal lattice followed by dehydrogenation to afford the product 5. In the case of the led crystal 4, the radical coupling is difficult because of the longer coupling distance of 5.6 Angstrom and the more restricted movement in the rigid crystal lattice. The results indicate that the observed photochemical behaviour of 3 and 4 are controlled by the molecular arrangement in the crystal lattice.

DOI： 10.1039/a701221g

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Language：English   Publisher：ELSEVIER SCIENCE BV  

The excited state dynamics and interfacial electron transfer of an optically scattering TiO2 powder suspension in alkaline water (pH = 10) with and without methyl viologen (MV2+) as an electron acceptor was examined by means of femtosecond diffuse reflectance absorption spectroscopy using a femtosecond white-light continuum as a probe pulse. The spectral analysis of broad transient absorption bands directly proved plural trapping sites of electrons with different electronic structure and surface electron transfer from photoexcited TiO2 particles to adsorbed MV2+ molecules in the few picoseconds to nanosecond timescale. (C) 1997 Elsevier Science B.V.

DOI： 10.1016/S0009-2614(97)00752-5

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Language：English   Publisher：AMER CHEMICAL SOC  

This paper discusses how the solvent-induced rapid relaxation of the initial delocalized excited state of 9-(4N,N-dimethylaminophenyl)phenanthrene (9DPhen), obtained immediately after picosecond pulsed excitation, can be resolved by means of femtosecond transient absorption experiments. The results obtained for 9DPhen are compared to the results of a sterically hindered compound 4-(9-phenanthryl)-3,5-N,N-tetramethylaniline (3,5Me9DPhen) in order to get more information about the possible conformational relaxation process suggested for these compounds. From the results of the femtosecond transient absorption experiments? a possible model is proposed to characterize the kinetic behavior of these molecules. After photoexcitation of 9DPhen and 3,5Me9DPhen, the distribution of higher excited states shows a fast transition within a femtosecond timescale to a ''hot'' charge transfer state. This state looses excess energy by a relaxation process (electronic and/or vibrationally and/or conformationally relaxation) on picosecond timescale. From this relaxed excited charge transfer state, fluorescence and intersystem crossing to a triplet state originate simultaneously and in competition. From the comparison of the steady state absorption spectrum of 9DPhen and 3,5Me9DPhen, as well as the transient absorption spectra of the triplet state, one can distinguish the quite different nature of the ground and the triplet state in both compounds. The bathochromic shift of the emission spectrum of both compounds suggests a larger excited-state dipole moment for 3,5Me9DPhen compared to 9DPhen. The lower values of the radiative rate constant [k(f)] and the longer decay times of 3,5Me9DPhen correlate with a less allowed radiative transition compared to that of 9DPhen. It is suggested that for 3,5Me9DPhen, the emissive state mixes to a smaller extent with a state with a strongly allowed transition and/or that the average angle between the phenyl and phenanthrene moieties of the excited state is larger (farther away from 0) than in the unsubstituted molecule, leading to a less allowed transition and a smaller value of the rate constant of fluorescence.

DOI： 10.1021/jp9702560

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Language：English   Publisher：AMER CHEMICAL SOC  

Charge recombination (CR) kinetics of photogenerated ionic species in poly(N-vinylcarbazole) (hereafter abbreviated as PVCz) film doped with an electron acceptor is investigated by transient absorption spectroscopy in the submicrosecond to millisecond time regime. Characteristic initial concentration dependence of the CR kinetics is observed and is qualitatively explained by a spatially restricted hole-diffusion-controlled CR model. From the temperature dependence of CR kinetics combined with a charge transfer (CT) fluorescence decay measurement, it is concluded that a CR with a long-range electron-transfer mechanism occurs under low-temperature conditions. Applicability of a 3-D random walk model in an energy disordered lattice to the CR kinetics is examined by means of a Monte Carlo simulation technique, and it is found that the spatial restriction condition is necessary to reproduce the CR kinetics in a PVCz film.

DOI： 10.1021/jp970591o

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Language：English   Publisher：AMER CHEMICAL SOC  

Primary processes of photoexcited states in an alpha-sexithienyl film are investigated by femtosecond transient absorption spectroscopy and picosecond time resolved fluorescence spectroscopy. Four species are observed in the transient absorption measurement. A broad absorption that shows a very rapid relaxation (within a few picoseconds) is ascribed to a singlet Frenkel exciton state. An oscillating structure is also apparent immediately after excitation and is ascribed to the Stark effect induced by a charged species (ion pair state). The latter state decays within 200 ps and is replaced by a different oscillating structure that is due to a thermal effect induced by a dissipation of excess energy. Another band owing to a tripler state appears via a very rapid conversion from a higher singlet exciton state. Fluorescence decay curves are well fitted with lifetimes of the charged state, which indicates that most of the emission is brought about by the charge recombination process, and furthermore, a charge-transfer (CT) emission band that has not been reported is observed.

DOI： 10.1021/jp9609287

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Language：English   Publisher：AMER CHEMICAL SOC  

Transient absorption spectra of charge-transfer (CT) crystals between methyl- or methoxy-substituted benzene derivatives and pyromellitic dianhydride (PMDA) were measured by femtosecond diffuse reflectance spectroscopy, and the electronic structure and dynamics of the excited state depending on the nature of the electron donor (D) are discussed. For such weak CT complexes, it was confirmed that excitation energy is localized in one donor-acceptor pair and the mixing of CT and locally excited (LE) configurations is important in the excited CT singlet state. The CT degree of the excited state depends on the oxidation potential of D and on the mutual configuration of D and electron acceptor (A) molecules. The second-order decay constant of the excited state was observed under usual photolysis conditions, from which a motion-limited diffusion was considered, A first-order decay of the transient absorption was obtained, when the excitation intensity was weak, and ascribed to charge recombination to the ground state, The energy gap (-Delta G) dependence of the charge recombination rate constant (k(CR)) was confirmed to give a linear relationship between Ln(k(CR)) and \-Delta B\.

DOI： 10.1021/jp961974+

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Language：English   Publisher：CHEMICAL SOC JAPAN  

Photocoloration of microcrystalline powder of a spirooxazine compound by femtosecond laser pulse excitation, depending on its intensity, is reported with transient absorption spectral measurements of the powder. The mechanism is discussed in terms of light induced local heating and succeeding cooling of a small volume in the microcrystal.

DOI： 10.1246/cl.1997.1165

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Language：English   Publisher：CHEMICAL SOC JAPAN  

Transient diffuse reflectance spectroscopic analysis using a femtosecond white-light continuum as a probe pulse was applied to commercially available catalysts of TiO2 powder; ''standard TiO2 catalysts'' (JRC-TIO-2 and -4) supplied by the Catalysis Society of Japan. The ultrafast dynamics of photogenerated charge carriers under vacuum and air conditions was compared and discussed.

DOI： 10.1246/cl.1997.735

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Diffusion-controlled scavenging of mobile holes under no applied electric field was observed directly in poly(N-vinylcarbazole) films, doped with 1,2,4,5-tetracyanobenzene (TCNB) as an electron acceptor and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) as a hole scavenger, by transient absorption spectroscopy. The scavenging of holes occurs mainly over several nanoseconds, and is complete within 1 mu s. The mean diffusion length of the migrating holes was estimated to be similar to 15 Angstrom. A Monte Carlo simulation of 3-D diffusion in energetically disordered media was applied for analyzing the hole-scavenging behavior. The spatially restricted character of the hole migration was revealed by the simulation. A very slow (up to several tens of milliseconds) recombination of TMPD cations with TCNB anions was also observed, which was explained in terms of a long-range electron tunneling.

DOI： 10.1021/jp9608943

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Language：English   Publisher：ELSEVIER SCIENCE BV  

Transient absorption spectra of the durene-pyromellitic dianhydride (PMDA) charge transfer (CT) crystal, PMDA-doped durene crystal and its molten state were measured by femtosecond diffuse reflectance spectroscopy, and electronic structure and dynamics of the excited state in the CT crystal are discussed. It is directly confirmed that the excited CT singlet state is almost localized (self-trapped) in one donor(D)-acceptor(A) unit within a few picoseconds after excitation. The electronic structure of the excited state is quite polar but it is not an electron transfer state from D to A.

DOI： 10.1016/0009-2614(96)00441-1

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Language：Japanese   Publisher：The Laser Society of Japan  

A recent development of ultrafast laser spectroscopy for highly light sattering materials is presented. Utilizing a stable femtosecond Ti: sapphier laser system has made it possible to get information about the dynamics of short-lived transient species in powder materials such as polymer latex perticles and organic microcrystals with a few ps temporal resolution. Time-resolved measurements of a diffuse reflected pulse with high temporal resolution are another important application of femtosecond laser technique. Its potential application toimaging and space- and time-resolved spectroscopy of the materials are described.

DOI： 10.2184/lsj.24.796

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Language：English   Publisher：ELSEVIER SCIENCE BV  

Transient diffraction spectra and their rise and decay dynamics of a thin copper phthalocyanine film (approximate to 50 nm thickness) were investigated by femtosecond transient grating spectroscopy using a white-light continuum as a probe pulse. Temporal profiles of first- and second-order diffractions were strongly dependent on the excitation intensity, which was interpreted in terms of exciton-exciton annihilation with a time-dependent rate constant.

DOI： 10.1016/0009-2614(95)00047-8

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Charge recombination dynamics of photogenerated ionic species in poly (N-vinylcarbazole) films doped with an electron acceptor was investigated by transient absorption spectroscopy in the microsecond to millisecond time region. The absorption decay was independent of the concentration of the ionic species and approximately obeys a t(-1/2) time dependence. The observed recombination process was well interpreted in terms of hole diffusion-controlled geminate recombination process.

DOI： 10.1016/0009-2614(94)01424-T

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Language：English   Publisher：AMER CHEMICAL SOC  

The energy pp dependences Of k(CR) (charge recombination rate constant) of CIPs (compact ion pairs) produced by exciting CT complexes of acid anhydride-aromatic hydrocarbon systems were investigated in solutions of different polarities and compared with those of the intramolecular IP states in distance-fixed porphyrin-quinone dyads10 as well as those of aromatic ligand to ligand intramolecular ET (electron transfer) states in Re(I) complexes.16b,c,17b No or very little solvent polarity effect on the k(CR) vs (energy gap) relation of CIPs was observed, which was very similar to the result of the intramolecular ET systems10,17b and suggested a dominant effect of the high-frequency quantum modes in the ET process. A ln(k(CR)) vs (energy pp) linear relation was observed for CIPs and interpreted on the basis of the weak coupling limit in the radiationless transition, including the important contributions of the multimode effects and the equilibrium displacements enhanced by ET, which was also very similar to the case of the Re(I) complexes.

DOI： 10.1021/j100152a016

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Language：English   Publisher：AMER CHEMICAL SOC