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Uniaxial alignment of crystalline nanowires consisting of N,N′ -dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) was achieved on poly(tetrafluoroethylene) (PTFE) layers prepared by friction transfer method on a glass substrate. The nanowires were formed by spin-coating a trifluoroacetic acid (TFA) solution of PTCDI-C8 on the PTFE layers and were further grown under TFA vapor atmosphere. The morphology of the PTCDI-C8 nanowires were characterized using atomic force microscope (AFM) and fluorescence optical microscope with changing the dye concentration in the spin coating solution, annealing time in the TFA vapor, and substrate materials. The nanowires prepared on the PTFE layer on a silica-coated silicon or a mica substrate did not grow so well as those on the glass substrate. This result suggests that the surface roughness would affect the PTFE layer and the growth of the PTCDI nanowires.

The considerably conjugated π systems of the group 14 dithienometallole-linked ethynylene-conjugated porphyrin dimers (1Ms) were described based on comprehensive experimental and theoretical studies. The electronic absorption spectra of 1M displayed a large splitting in the Soret band and a red-shifted Q-band, indicating that the dithienometallole spacer was effective in facilitating the porphyrin–porphyrin electronic coupling. Torsional planarization behaviors of 1M were observed in the time-resolved fluorescence spectra. Density functional theory (DFT) calculations revealed that the dithienometallole spacer is an ideal partner for the ethynylene-conjugated porphyrin to produce fully delocalized highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels due to their similar HOMO and LUMO levels. Finally, 1M exhibited a strong propensity for the quinoidal–cummulenic conjugation in the dithienometallole spacer when in a photoexcited state.

The photon antibunching behavior in the photoluminescence (PL) of single CdSe/ZnS semiconductor nanocrystals (NCs) interacting with the localized surface plasmon resonance (LSPR) of Ag nanostructure was investigated using fs-pulsed laser excitation at two excitation wavelengths. The time traces of the PL intensity, the PL decay curves, and the photon correlations of single NCs on a rough Ag film and on a coverslip were measured simultaneously, and an increase in the PL intensity accompanied by shortening of the PL lifetime was observed for the single NCs on the rough Ag film. The enhancement factor of the PL intensity depended on the excitation wavelength. Nearly all of the single NCs with enhanced PL exhibited photon antibunching behavior independent of the enhancement factor. Based on the enhanced radiative- and nonradiative-decay rates estimated from the experimental data, the mechanism of the photon antibunching behavior was considered as follows. To exhibit the photon antibunching behavior, the nonradiative Auger recombination between the generated excitons in a single NC is important. When the radiative- and the nonradiative-decay rates enhanced by the LSPR are faster than the Auger recombination rate, the probability of photon antibunching decreases. However, such fast radiative- and the nonradiative decay rates were not observed for single NCs interacting with the LSPR of the rough Ag film in this work. Therefore, the PL intensity from a single NC can be increased while maintaining the photon antibunching behavior. Our findings assist in the creation of effective single-photon sources and provide important information on the emission properties of an NC coupled with the plasmon of a metal nanostructure.

Extremely pure polymer matrices were used for elucidating the fluorescence properties of singly isolated charge-transfer (CT) complexes formed between the donor N-ethylcarbazole and the acceptor 1,2,4,5-tetracyanobenzene. Simultaneous measurements (time traces of CT fluorescence intensities and lifetimes) using single-molecule fluorescence spectroscopy showed three patterns: (1) fluctuations in the fluorescence intensities and lifetimes seldom occurred, (2) the fluorescence intensities frequently fluctuated together with the lifetimes, or (3) in addition to the above fluctuations with time, blinking and/or off-states longer than 1 s were observed. For methacrylate polymers, both the degree of fluctuations in the CT fluorescence lifetimes and the percentage of the CT complexes showing off-states increased with the free volume of the host polymers. These results suggest that the degree of fluctuations in the relative geometrical arrangements of the donor and acceptor molecules is related to the availability of space in the host polymer, and that the free volume provides the necessary space for formation of non-fluorescent donor–acceptor geometries of the CT complexes and/or temporal dissociation of the CT complexes. Survival times of the CT fluorescence were also closely related with the free volume of the host polymers.

To reveal the exciton dynamics, particularly multiexciton dynamics in single colloidal CdSe/ZnS quantum dots (QDs) interacting with the localized surface plasmon resonance (LSPR) of silver nanoparticles (AgNPs), we investigated the single-photon emission behavior in the fluorescence from the single QDs using a single-molecule spectroscopy technique in combination with a femtosecond-pulsed laser excitation. By applying simultaneous measurements of the photon-correlation (photon antibunching), the fluorescence intensity, and the fluorescence lifetime to the single QD near AgNPs, we revealed that the probability of single-photon emission strongly depended on the fluorescence lifetime; that is, the probability of single-photon emission decreased when the lifetime was shorter than subnanoseconds. On the basis of the estimation of both radiative and nonradiative decay rates enhanced by the LSPR, the following mechanism was suggested. In the absence of AgNPs, multiple excitons generated by a high-power excitatio...

Single molecule fluorescence spectroscopy (SMS) was used to elucidate the fluorescence dynamics of singly isolated charge-transfer (CT) complexes formed between various monocarbazolyl and dicarbazo...

Single-photon behavior in the emission from a single nanoparticle consisting of a single poly[2-methoxy-5-(2′-ethylhexyloxy)- p -phenylene vinylene] (MEH-PPV, molecular weight: 2,600,000 amu) chain has been investigated. Photon correlation measurements of a number of single nanoparticles revealed that the probability of single-photon emission from the single nanoparticles clearly increases, compared with that of single chains embedded in host polymer matrices, poly(methyl methacrylate) (PMMA) and polystyrene (PS). The result suggested that even a single MEH-PPV chain with high molecular weight, which does not exhibit single-photon emission in PMMA and PS, is forced to exhibit single-photon emission by adopting “compact” chain conformation like nanoparticle. Efficient exciton migration and exciton annihilation processes in the compact chain conformation most probably result in the efficient single-photon emission from the single nanoparticle. The present results indicate that multi-quantum systems consisting of a large number of chromophores, such as the MEH-PPV, can be made to behave as single-photon sources by appropriately controlling their size.

4-Cyano-4′-(1-(1-pyrenyl)- n -octyloxy)biphenyl (8OCBPy), where the hydrogen atom of a well-known mesogen 4-cyano-4′- n -octyloxybiphenyl (8OCB) is substituted with one pyrenyl (Py) chromophore, was synthesized. When 8OCBPy was doped in the mesophases of the similar mesogen of 4-cyano-4′- n -decyloxybiphenyl (10OCB), the Py chromophores should be oriented by a constraint in the mesophases as compared with free chromophores dispersed in the mesophases. The binary mixture exhibited smectic A (Sm A) and nematic (N) mesophases. The mesophases and isotropic (I) phase of the binary mixture exhibited excimer as well as monomer fluorescence. The intermolecular excimer formation-dissociation kinetics of 8OCBPy in the Sm and I phases of its binary mixture was investigated in comparison with that for a 1-ethylpyrene binary system. Positive enthalpy and entropy changes for the excimer formation were found in the Sm A mesophase, whereas their usual changes were found in the I phase. These anomalous phenomena observed in the Sm A mesophase were interpreted by the entropy-controlled excimer formation associated with the decrease in ordering of the 10OCB-mesogen molecules around the 8OCBPy arranged in the Sm A layers.

We report the photoluminescence properties of polymer alternating multilayer films containing a fluorescent dye in one component. The alternating multilayer film with periodicity in both refractive indices and dye distribution showed 6 times higher intensity of amplified spontaneous emission than the multilayer film with periodicity in dye distribution only. Multilayer films that have a structure of Fabry–Perot resonator showed a lasing threshold of approximately 1.7 mJ cm − 2 .

We prepared nanoparticles of an organic dye, acridine orange (AO), dispersed in poly(methacrylic acid) (PMA) films by spin-coating the solution of the two components. The surface of the AO/PMA films became bumpier with increasing AO concentration (cAO). The absorption and fluorescence spectra of AO/PMA films exhibited a marked dependence on cAO at low cAO (cAO 2.1 × 10− 1 mol kg− 1). The peak shift of fluorescence spectra with changing cAO was as large as ∼ 100 nm.

The site-selective doping of dyes into spin-cast thin films with different phase separation structures of polystyrene-block-poly(4-vinyl pyridine) (PS-b-P4VP) diblock copolymers and the dopant-induced laser ablation of the dye-doped films fabricated were investigated. The selective doping of dyes into P4VP parts was carried out by immersing the films in a methanol solution containing the dyes, in which the driving force was induced by hydrogen bonds between the nitrogen atoms of pyridyl groups and the carboxylic groups of the dyes. Schematic models for the adsorption process of the dyes in the methanol solution were discussed. Dopant-induced laser ablation was carried out on the dye-doped block copolymer films, resulting in the ablation of dye-doped P4VP parts only. Factors affecting selective ablation, such as dyes, the morphologies of phase separation structures, the number-average molecular weights of the diblock copolymers, and irradiation environments, were discussed.

4-Cyano-4′-(1-( N -carbazolyl)- n -octyloxy)biphenyl (8OCBCz), where the hydrogen atom of a well-known mesogen 4-cyano-4′- n -octyloxybiphenyl (8OCB) is substituted with one carbazolyl (Cz) chromophore, was synthesized, and the photophysical and photoconductive properties of its neat form and its binary mixtures with 4-cyano-4′- n -decyloxybiphenyl (10OCB) were investigated. The 8OCBCz exhibited intermolecular exciplex fluorescence in concentrated solutions. When 8OCBCz was quenched from its molten state, it formed an amorphous state, which exhibited exciplex fluorescence and transient photocurrent signals of both the positive and negative charge carriers. However, their mobilities could not be determined because of the strongly dispersive signals. The mixtures exhibited smectic A (Sm A) and nematic (N) mesophases. These mesophases and the isotropic phase exhibited exciplex as well as monomer fluorescence. The exciplex formation mechanism in the Sm A mesophase differed from those in the N and isotropic phases. The transient photocurrent signals for both the positive and negative charge carriers were also observed for the binary mixtures. Ionic conduction was suggested for the N and isotropic phases, whereas electronic conduction was suggested for the Sm A mesophase. The ionic carrier species were proposed.

Laser irradiation using a Nd3+:YAG laser (532 nm, 8 ns, 10 Hz) on an ethanol suspension of micrometer-sized pentacene crystals induced absorption spectral changes in the solution, as a result of the formation of pentacene nanoparticles. The nanoparticles were platelike crystals. The nanoparticles formed by irradiation with a fluence of 50 mJ/cm2 for 30 min were 4–13 nm in height and 10–70 nm in width. The threshold laser fluence for the formation was determined to be ca. 20 mJ/cm2, and irradiation with fluences above 80 mJ/cm2 induced the decomposition of the pentacene nanoparticles. The nanoparticle size decreased with an increase in the laser fluence, which was reflected in the longest-wavelength peak position of the absorption bands of the pentacene nanoparticles. On the basis of these results, the mechanism of pentacene nanoparticle formation by laser irradiation is discussed in connection with those of vanadyl phthalocyanine and quinacridone systems reported by Masuhara and coworkers [J. Phys. Chem. A 106 (2002) 2135; Jpn. J. Appl. Phys. 42 (2003) 2725; Jpn. J. Appl. Phys. 45 (2006) 384].

A fluorescent polystyrene microsphere with a diameter of 20 nm whose surface is modified with carboxylic acid groups was arranged selectively on one component of a diblock copolymer film of polystyrene and poly(4-vinylpyridine) (P4VP). Atomic force microscopy (AFM) observations showed that the microsphere was adsorbed only to the island part corresponding to the P4VP phase of the microphase structure of the film due to hydrogen bonding between the carboxylic acid groups of the microsphere and the pyridyl groups of P4VP. When the diameter of the microsphere was 50 nm, the microsphere was rarely adsorbed to the block copolymer film.

Tetrakis-5,10,15,20-(4-carboxyphenyl)porphyrine (TCPP) was position-selectively introduced into a diblock copolymer film of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) with a sea–island microphase structure. By immersing the PS-b-P4VP film into a solution of TCPP/methanol, TCPP was introduced into the island parts comprising P4VP phase. The morphology of the island parts depended on the immersion time and TCPP concentration. A schematic model for the morphological change caused by the phase-selective introduction of TCPP was proposed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 368–375, 2007

We investigated Si 2p spectra for the Si(1 0 0)c(4 × 2) surfaces exposed to CO and CO 2 to clarify how the adsorbed molecules affect the clean surface spectra in ultra-high vacuum (UHV). After a small amount of CO exposure (0.05 L), the spectral shape looks sharper as compared with that of the clean surface due to the reduced intensity of the down dimer peak, because CO is preferentially adsorbed on the down dimer site. Thus the adsorption of CO from the residual gas in UHV might induce a slight change in the spectral shape within a measurement period (∼10 3 s). On the other hand, in the case of adsorbed CO 2 , the spectral shape does not change but the overall intensity decreases, since CO 2 is physisorbed on Si(1 00).

Nanoscopic aggregation in random copolymers of methyl methacrylate (MMA) with n-butyl methacrylate (n-BMA) or benzyl methacrylate (BzMA) in bulk films has been studied for the first time at low temperatures by using photochemical hole burning (PHB) spectroscopy for tetraphenylporphine (TPP) dispersed in the copolymers and also with transmission electron microscopy (TEM). Temperature cycle experiments with PHB were carried out for the copolymers with different ratios of comonomer groups. The increases in hole widths due to structural relaxation of butyl groups or benzyl groups in the copolymers of n-BMA or BzMA with MMA were much larger than those expected for hypothetical systems where MMA and comonomer groups with the corresponding molar ratios are randomly dispersed. The results have been attributed to the nanoscopic aggregation of n-BMA or BzMA units with the preferential inclusion of TPP within them in the films. PHB spectroscopy provides a new tool for studying nanoscopic aggregation larger than 2.3 ...

We have investigated the C 1s photoelectron spectra of ethylene on the Si(1 0 0)(2 × 1) surface, using high resolution photoelectron spectroscopy. The vibrational structure has been observed in the C 1s spectra where the C–H stretching mode is dominant. The vibrational splittings of C 1s ionized state are very similar to those in the ground state. It is found that linear coupling model is applicable in this system and this excitation process is a Frank–Condon process. The curvature of potential energy surface of C–H and C–D bond is almost unchanged upon core ionization.

A nematic liquid crystal doped with a chiral dopant has a cholesteric texture with a regular pitch. The pitch is changed by variation of concentration of the dopant. We observed the appearance of a fingerprint texture on irradiation of a homeotropic mixed liquid crystal doped with a racemic chromium complex, Cr(Buacac)3, and an auxiliary chiral dopant, with right-circular polarized light (r-CPL); the fingerprint texture disappeared on irradiation with left-circular polarized light (l-CPL). We also measured a helical twisting power, βm, of the chromium complex from the cholesteric pitch of the mixed liquid crystal doped with optically resolved Λ -(Cr(Buacac)3; and clarified the relationship between the change in the cholesteric pitch and the quantum yield of the photoinversion reaction.

Core-shell type microspheres with fluorescent dansyl groups at random sites in crosslinked poly(N-isopropylacrylamide) (PNIPAM) shell chains and core-hair type microspheres with dansyl groups at terminal sites of PNIPAM hair chains graft-polymerized with living-radical mechanism were prepared. Fluorescent spectra indicating the microenvironments of dansyl groups attached to the microspheres and their dependences on temperature and solvent compositions were compared to those of dansyl groups in PNIPAM bulk gels and in free solutions. Fluorescence peak wavelength of dansyl groups in the core-shell type microspheres showed an extraordinary blue shift in water, suggesting that dansyl groups are incorporated in the semi-interpenetrating polymer network (SIPN) region of the core-shell boundary. This is supported by a confocal laser-scanning fluorescence microscope (CLFM) image of a single particle for the core-shell type microsphere. Dansyl groups at the chain ends of PNIPAN hairs of the core-hair type microspheres in water are also located on the surface of hydrophobic cores.

Cytochrome b562 and three of its mutants in which only one amino acid is substituted were studied with persistent spectral hole burning. Structural relaxation at low temperatures was evaluated by performing temperature cycling experiments from 22 up to 100 K. There are remarkable differences in spectral diffusion behavior between the wild type and the mutants (N6D at 35 K and M7C above 60 K). The relaxation of the –OH group in N6D (asparagine 6 is replaced by aspartic acid) which occurs at 35 K at the site 10 A vertically apart from the protoporphyrin ring is reflected by an increase in holewidth of 0.3 cm−1. The relaxation of the –SCH3 groups of methionine 7 in wild type cytochrome b562 was found to occur at 60 K by comparing the results with those of M7C (methionine is replaced by cysteine).

We report the results of persistent spectral hole burning (PSHB) at 4 K in the isolated photosystem II reaction center complex (PSII RC) in the presence and absence of externally added dibromothymoquinone DBMIB (2,6-dibromo-3-methyl-5-isopropyl-p-benzoquinone). The purified PSII complex (D1–D2–cytochrome b559 reaction center complex) has six molecules of chlorophyll a and lacks intrinsic electron acceptor plastoquinone (designated QA and QB, respectively). DBMIB replaces the function of QA. The efficiency for the hole formation at a long wavelength (680 nm) was higher than that at a shorter wavelength (671 nm). Addition of DBMIB lowered the efficiency at shorter wavelengths (671–674 nm) with little effect at longer wavelengths (677–680 nm). Temperature excursion experiments at 4–30 K indicated the higher temperature stability of the hole at the longer wavelength suggesting that the extent of thermally induced backward reaction of hole formation, i.e., the structural relaxation behavior of the matrix around the pigments was smaller at the longer wavelength. The hole burned at 671 nm can be attributed to the pheophytin in D2 subunit, while the hole at 680 nm to the electron-acceptor pheophytin in D1 subunit. The possibility remains that the peripheral Chl 667 is responsible for the hole at 671 nm. The temperature dependence of Debye–Waller factor also suggested that the PSII RC complex has stronger electron–phonon interaction than usual amorphous polymer systems.

A novel preparation approach for high-performance polyimide gels that are swollen or have a jungle-gym-type structure is proposed. A new rigid and symmetric trifunctional amine, 1,3,5-tris(4-aminophenyl)benzene (TAPB), was synthesized as a crosslinker. Three different kinds of amic acid oligomers derived from pyromellitic dianhydride (PMDA), 4,4′-oxydiphthalic anhydride (ODPA), p-phenylenediamine (PDA), and 4,4′-oxydianiline (ODA) were end-crosslinked with TAPB at a high temperature to make polyimide networks with different structures. Transparent polyimide gels were obtained from the ODPA–ODA/TAPB series with high compression moduli of about 1 MPa at their equilibrium swollen states in N-methylpyrrolidone. Microscopic phase separation occurred during the gelation–imidization process when polyimide networks were generated from PMDA–PDA/TAPB and PMDA–ODA/TAPB. After these opaque polyimide networks were dried, a jungle-gym-like structure was obtained for the PMDA–PDA/TAPB and PMDA–ODA/TAPB series; that is, there was a high void content inside the networks (up to 70%) and little volume shrinkage. These polyimide networks did not expand but absorbed the solvent and showed moduli as high as those of solids. Therefore, using the highly rigid crosslinker TAPB combined with the flexible monomers ODPA and ODA and the rigid monomers PMDA and PDA, we prepared swollen, high-performance polyimide gels and jungle-gym-type polyimide networks, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2501–2512, 2002

We report the first results of persistent spectral hole burning of dendrimer porphyrins having three-, four-, or five-layered aryl ether dendritic arrays. We evaluate structural relaxations of dendrimer framework around the porphyrin core at low temperatures. A large environmental change around the porphyrin core, as evaluated from the hole area, was suppressed in dendrimer porphyrins of higher generation numbers, whereas a small environmental change, as evaluated from hole width, showed no dependence on the number of generations. The dendrimer porphyrins showed sharp holes at 20 K, suggesting a long dephasing time and the suppression of spontaneous spectral diffusion. The results of dendrimer-embedded polymer sample indicated that the structural relaxation of polymer chain outside the dendrimer does not have an influence on the resonant frequency of the porphyrin core. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 210–215, 2002

In this article, our recent results of the application of near-field scanning optical microscopy (NSOM) to the photochemistry in small domains and single polymer nanoparticles are presented. After an introduction and the description of our apparatus, results on three topics are presented: (1) Control and observation of a photoacid generation from p-nitrobenzyl 9,10-dimethoxyanthracene-2-sulfonate (NAS) in a polymer thin film, (2) Patterning due to refractive index changes by a photoisomerization of 3-phenyl-2,5-norbornadiene-2-carboxylic acid (PNCA) (3) NSOM observation of moving nanoparticles at a liquid/solid interface.

Nanoscopic aggregation and highly constrained nanoenvironments within bulk films of amphiphilic random copolymers have been studied for the first time by using photochemical hole burning spectroscopy at low temperatures. Films containing sodium sulfonate (A) and cyclododecyl (CD) or lauryl (LA) groups) with tetraphenylporphine (TPP) dispersed in the copolymers, as well as for TPP covalently bound to the copolymer chains, were prepared. Temperature cycle experiments were carried out for the copolymer films with different ratios of the hydrophilic and hydrophobic groups. Holes burned in the copolymer films with CD and sodium sulfonate groups were thermally more stable than those expected for hypothetical systems where the groups are randomly dispersed with the corresponding ratios. The discrepancy can be attributed to the “pinning down” of TPP in constrained configurations of CD aggregation in the films. On the other hand the increase in hole width in the copolymer films of LA groups with sodium sulfonate was enhanced compared to those expected for hypothetical systems where sodium sulfonate and LA groups are randomly dispersed with the corresponding ratios. The results could be attributed to the aggregation of LA groups, with the preferential inclusion of TPP within it, in the films.

Steady-state photocurrent in poly(N-vinylcarbazole)(PVCz) (26,48 wt%)/poly(methyl methacrylate)(PMMA) blends is for the first time measured. The PVCz(26,48 wt%)/PMMA blends showed almost the same carrier-generation efficiencies at electric fields higher than 1 × 105 V · cm−1. The results are explained by high miscibility of the PVCz(26,48 wt%)/PMMA blends, suggesting the existence of PVCz chains in continous PMMA-rich phase in the phase-separated structure. The miscibility is also evaluated by means of excimer fluorescence of PVCz in these blends and fluorescence microscopy.

A large photo-induced refractive index changes as large as 0.014 at 632.8 nm in thermostable transparent polymer films has been realized for the first time by using photoirradiation of polymide precursor films containing a phenylazid and successive imidization. The phenylazide fragment forms a charge-transfert complex with imide moiety. The films maintained high transmittance in a wide visible region in constrast to usual polyimide films. This value of refractive index change is sufficient to make thermostable channel waveguides and other optical devices.

Photon-correlation measurements were applied to single chains of poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylene vinylene] of various molecular weights in a fluid solvent in order to investigate the...

Solvents with limited solubility for N,N'-di(octyl)perylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C8) were used for laser ablation in liquid. Laser irradiation of the suspension induced an absorption spectral change of the solution. The absorbance of free PTCDI-C8 molecules in the solution obtained by laser irradiation was unusually larger than that of the suspension before laser irradiation, suggesting that a supersaturated solution was formed by laser irradiation of PTCDI-C8 nanoparticles prepared by laser ablation.

We have investigated low-temperature structural relaxation in polysiloxane matrices by using persistent spectral hole burning (PSHB). The irreversible increase in hole width and the irreversible decrease in hole area were evaluated in terms of PSHB temperature-cycling experiments starting at 4 or 20 K. MQ-type silicone resins containing cross-linked nanoparticles (an uncured prepolymer mixture and cured MQ resins) and poly(methylphenylsiloxane) (PMPS) were used. The increase in hole width was observed at 15–20 K for all measured polysiloxanes. The increase is attributed to the local relaxation originating from the siloxane chains. The local structural relaxation of siloxane chains in this temperature range is confirmed for the first time. The local structural relaxation observed in the PSHB can be related to the rapid decrease in the final cis fraction between 4 and 20 K observed in the previous azobenzene photo-isomerization study. The curing effects of the MQ resin on the local relaxation are also discussed.

It is for the first time found that poly(N-vinylcarbazole)(PVCz)/polystyrene (PS) blends have lower miscibility on molecular level than that of PVCz/polyoxyethylene (PEO) blends. This is obtained from excimer fluorescence properties of PVCz in PVCz (9.1-100%)/PS and PVCz (9.6-100%)/PEO blends. Schematic diagrams of phase-separated structure of the PVCz blends are proposed consistent with emission properties and phase-contrast microscopic images.

We investigated the local structure and dynamics of three-dimensionally crosslinked polysiloxane, an MQ-type silicone resin, using fluorescence depolarization of perylene molecularly dispersed in the resin. Rotational diffusion coefficient, Dr, of perylene was determined in uncured and cured MQ resins and in PMMA over a temperature range of 90-300K. Dr in the uncured MQ resin (a mixture of prepolymers), i.e., an assembly of crosslinked nanometer-scale particles, is 5-10×108S-1 at room temperature and shows continuous drastic decrease with decreasing temperature to 106S-1 at 90K. Dr in the cured MQ resins is 107S-1 and almost independent of temperature. Dr in the cured MQ resins is thus larger than that in the uncured prepolymer at 90K. A possible explanation is as follows. The thermal fluctuation of nanoparticles caused by the Si-O-Si chain flexibility becomes weak with decreasing temperature in the uncured prepolymer, and change in packing and dense aggregation of the nanoparticles around perylene molecules cause the gradual increase in restriction against rotation of perylene from room temperature to 90K. In the cured MQ resins, hydrosilylation curing reaction would fix the spatial position of the nanoparticles and retain the local space around perylene even at low temperatures. The results of fluorescence depolarization are compared with those of photoisomerization of azobenzene in the MQ resin in our previous study.

Some miscibility between poly(N-vinylcarbazole) (PVCz) and poly(oxyethylene) (PEO) has been found for the first time by means of the two kinds of excimer emission of 8.0-100 wt% PVCz in the PVCz/PEO blends. Interchain energy migration to a full-overlap excimer site in the blends is suggested on the basis of time-resolved fluorescence spectra. The emission ratio between partial-overlap and full-overlap excimers shows PVCz concentration dependence similar to that of film transparency, reflecting chain aggregation in PVCz/PEO blends. Schematic diagrams of microscopic phase-separation structure of the blends for various PVCz contents are also proposed.

We performed persistent spectral hole burning for a free-base porphyrin (TMPyP) doped in a DNA-lipid complex film. The microscopic environments of the TMPyP intercalating or outside-binding to the double helix of the DNA-lipid complex is evaluated. The real inhomogeneous width for the TMPyP/DNA-lipid complex is similar to that for a TMPyP/poly(vinyl alcohol) system. In temperature cycling experiments the hole begins to broaden at 40 K, whereas the hole area does not show marked decrease below 100 K. The irreversible hole broadening is attributed the relaxation of the alkyl chain in the lipid part. No decrease in hole area during the temperature cycle is supposed to reflect the binding structure of the TMPyP molecules to the double helix in the DNA-lipid complex.

We measured the real inhomogeneous widths of the distribution composed of purely electronic zero-phonon absorption components alone by using persistent spectral hole-burning of tetraphenylporphine doped in several polymers. The correlation between the inhomogeneous widths and the dye-polymer intermolecular interactions is discussed by using a statistical theory. From the results, the main contribution to the inhomogeneous broadening is evaluated to be the van der Waals interaction, and the contribution of the dipole-dipole interaction increases with the polarity of polymers. We also evaluated a linear correlation between the inhomogeneous widths and the solubility parameters of the polymers, which express the strength of the intermolecular interactions.

The highly constrained microenvironment and the dependence of the structural relaxation and electron-phonon interaction on the distance between the chromophores and the matrix around them in unimolecular micelles (unimers) of amphiphilic random terpolymers containing sodium sulfonate, cyclododecyl (CD) and a small amount of tetraphenylporphine (H 2 TPP) groups were studied at low temperatures using photochemical hole burning spectroscopy. The radii of the terpolymers micelles were controlled, and they were embedded in poly(vinyl alcohol). The terpolymers with CD groups form unimers in the polymer matrix. We also measured the homopolymers containing CD or sodium sulfonate groups doped with H 2 TPP or sodium salt of sulfonated tetraphenylporphine (TPPS). The burned holes were thermally more stable in the unimer with CD clusters than those both in CD homopolymers and in the hypothetical system where the sodium sulfonate and CD groups are randomly dispersed. The results were attributed to the pinning down of the H 2 TPP species to constrained configurations in the CD cluster. The phonon frequency and the inhomogeneous width are independent of the micelle's radii in the present experiment condition. Then we conclude that the electron-phonon interaction and intermolecular interaction including van der Waals interaction and dipole-dipole interaction are effective within 2.3 nm in the present system.

We have investigated the local free volume of an MQ-type silicone resin consisting only of M (R 3 SiO 1/2 ) and Q (SiO 4/2 ) units by using photoisomerization of azobenzene molecularly dispersed in the matrices. Photoisomerization profiles in the uncured and cured MQ resin over a wide temperature range (4–300 K) are discussed based on three parameters: first-order plots, final cis fraction and quantum yields for trans-to-cis photoisomerization of azobenzene. For uncured MQ resins or prepolymers, for which the structure was proposed to be an assembly of crosslinked nanoparticles, a large fluctuation of local free volume was observed between room temperature and 20 K. At 4 K, a drastic decrease in the final cis fraction was observed in both the uncured prepolymer mixture and the cured MQ resin, implying the complete suppression of the free-volume fluctuation at 4 K. The formation of heterogeneous sites after curing is shown by the deviation from first-order kinetics for the cured MQ resins. Data for the cured MQ resin are analyzed quantitatively with the three-component approximation and the validity of a free-volume fluctuation model is verified. Comparison of the results for linear polysiloxanes with those for poly(methyl methacrylate) shows that siloxane chains are very flexible at low temperatures down to 20 K.

Persistent spectral hole burning spectroscopy is applied to evaluate the low-temperature relaxation around the dye molecules doped in several types of polymers. The doped dye is tetraphenylporphine, and the measured polymers are vinyl polymers and main chain aromatic polymers. The changes of microscopic environments around the dye are evaluated from the changes in the hole profiles during temperature cycling experiments. The relaxation behavior of the polymers is discussed in relation to their chemical structures. (C) 1999 John Wiley & Sons, Inc.

Chiral aryl 4-tolyl sulfoxides substituted with several sizes of aromatic rings, (S)-(−)-phenyl 4-tolyl sulfoxide (PHSO), (R)-(+)-1-naphthyl 4-tolyl sulfoxide (NASO), (R)-(+)-9-phenanthryl 4-tolyl sulfoxide (PNSO), and (R)-(+)-1-pyrenyl 4-tolyl sulfoxide (PYSO), were prepared. It has turned out for the first time that there are n–σ*, π–σ* and π–π* states in excited states of these molecules by MO calculation. Fluorescence spectra and quantum yields of fluorescence, Φfl, were measured in polar and non-polar solvents. Quantum yields of photoinversion, Φinv, and photolysis, Φdec, were also obtained with CD and HPLC measurements. Aromatic-ketone like characteristics have been noticed in the fluorescence measurements, i.e., fluorescence has been observed from sulfoxides substituted with large aromatic rings and their fluorescence becomes strong in a polar solvent. We attributed these characteristics to the decrease in π–π* transition energy as the degree of conjugation increases, while n–σ* and π–σ* transition energy does not decrease so much. The values of Φinv and Φdec for PHSO, NASO and PNSO were found to be 0.3–0.4 (Φinv) and 0.03–0.05 (Φdec). The quantum yields for PYSO were measured as Φinv = 0.02–0.03 in methanol and hexane, and Φdec = 0.002–0.003 in methanol and 0.012–0.016 in hexane. It was found that quantum yields of photoinversion and photolysis decrease as the π–π* transition energy decreases. We concluded that photoinversion occur during change in electronic states from n–σ* states to the ground state.

We demonstrated that the emission from a single organic nanocrystal consisting of organic dye molecules shows photon antibunching. That is, an assembling structure consisting of many chromophores can also be made to behave as a single-photon source by controlling the size. We found that most of single nanocrystals within a size range from 35 to 85 nm show photon antibunching even when more than one exciton in a crystal is generated by an intense single excitation pulse. On the other hand, single micrometer-sized crystals showed no antibunching. The present results indicate that molecular assemblies can also be considered as candidates for new single-photon sources.

Time-resolved fluorescence polarization anisotropy (FPA) of two dyes (acridine orange and ethidium bromide) intercalated in a raw DNA and a novel DNA-lipid complex has been measured on nanosecond timescale to evaluate the effect of lipid molecules on the twisting motions of DNA helix. Steady-state fluorescence spectra show that intercalated dyes are not influenced much by solvents compared with free dyes, suggesting the similar microscopic environments of intercalated chromophores. The FPA decay times of both dyes are about twice larger in the DNA-lipid complex than in the raw DNA, which indicates that the lipid molecules around the helix make the twisting motion slower. The FPA decay profiles fit very well with double-exponential functions having time constants differing much with each other, suggesting that there exists slow and quick elements in the twisting motions.

We studied the highly constraining microenvironment in unimolecular micelles (unimers) of amphiphilic random terpolymers containing sodium sulfonate, cyclododecyl (CD) or lauryl (LA) groups, and a small amount of tetraphenylporphine (H 2 TPP) moiety at low temperatures by using photochemical hole burning spectroscopy. The terpolymers were embedded in poly(vinyl alcohol). Only the terpolymer with CD groups forms unimers in the polymer matrix. We also measured the homopolymers containing CD or LA groups doped with H 2 TPP. The burned (spectral) holes were thermally more stable in the unimer with CD clusters than in the terpolymer with LA groups and in the homopolymer with CD groups. The phonon frequency is larger in the unimer with CD clusters (15.9 cm -1 ) than in the homopolymer containing CD groups (12.5 cm -1 ). The results are attributed to the pinning down of the H 2 TPP species to constrained configurations in the CD cluster.

The photochemical behavior at cryogenic temperatures of phenoxazine and phenothiazine dyes in poly(vinyl alcohol) was investigated by using persistent spectral hole burning. The importance of hydrogen-bondings has been confirmed by measuring the effects of the addition of N,N,N′,N′-tetramethyl-p-phenylenediamine on the holewidth and the hole area of various cationic dyes at 20 K. The hydrogen bonds around the ring-N atom affect the total dephasing time, while the hydrogen bonds around the amino groups as the substituents and around the ring-N atom control the efficiency of hole formation.