Hiroshi Masuhara

Picosecond transient absorption spectral and kinetic study on benzophenone microcrystals by diffuse reflectance laser photolysis method

Abstract The absorption spectrum and formation dynamics of triplet benzophenone in microcrystals were measured for the first time by analyzing diffuse reflected spectra of the picosecond continuum. The absorption spectral shape is similar to that of 2-propanol solution, and no appreciable difference was observed in their rise curves.

Porphyrin-sensitized laser swelling and ablation of polymer films

Laser-induced morphological changes of poly(methyl methacrylate), poly(N-vinylcarbazole), and gelatin films doped with porphyrins have been studied by etch depth measurement and scanning electron microscopy. An irreversible swelling of the irradiated surface was observed for all films in the case of low laser fluence. The swelling was replaced by ablation when the fluence was increased. The etch depth depends on the irradiation fluence and the dye concentration in the polymer. The observation of the irradiated surfaces suggests that the thermal effect is predominant both for swelling and ablation. The surface temperature at which swelling or ablation is initiated was estimated, assuming that these morphological changes take place at a certain temperature for any dye concentration in each polymer film.

Picosecond dynamics of excited singlet states in organic microcrystals: Diffuse reflectance laser photolysis study

Absorption spectra and picosecond dynamics of the singlet exciton states of benzil and p-terphenyl in a microcrystal have been measured for the first time by analyzing the diffuse reflected spectra of the picosecond continuum.

Excimer dynamics of poly(n-vinylcarbazole) films revealed by time-correlated single photon counting measurements

Abstract Precise rise and decay curves of excimer emissions of poly (N-vinylcarbazole) films in the picosecond time region have been measured by using a time-correlated single photon counting technique. The partial overlap excimer fluorescence was observed immediately after excitation, while the sandwich excimer fluorescence showed delayed formation processes. These results were quite different from those reported before, discussed in terms of high intensity excitation and photo-oxidation effects.

Laser photolysis study on photoinduced charge separation in poly(N-vinylcarbazole) thin films

Abstract A laser photolysis method, monitoring transient absorption under total internal reflection condition, was developed and applied to poly(N-vinylcarbazole) thin films. Photoinduced charge separation was confirmed directly for polymer films doped with some electron acceptors. Absorption spectra composed of polymer cation and acceptor anion are ascribed to migrating hole and trapped electron, respectively, and their decay curves correspond to a homogeneous recombination process.

Fluorescence spectra of vacuum-deposited films of ω-(1-pyrenyl)alkanoic acids

Abstract Vacuum-deposited films of ω-(1-pyrenyl)alkanoic acids with different chain length were prepared using a deposition rate of ≈1 nm min . Their fluorescence spectra consist of pyrene monomer fluorescence and two new emissions; no excimer-like emission was detected as a major component. These fluorescence results are considered in terms of pyrenyl aggregates characteristic of a deposited film.

Fluorescence dynamics of charge-transfer-complex films of poly(N-vinylcarbazole) and 1,2,4,5-tetracyanobenzene and molecular aspects of the disordered structure

Abstract Charge-transfer (CT) fluorescence of poly( N -vinylcarbazole) (PVCz) films doped with 1,2,4,5-tetracyanobenzene was investigated in comparison with exciplex (and/or exterplex) fluorescence of PVCz films doped with 1,4-dicyanobenzene by using the nanosecond time-correlated single-photon-counting method. For excitation of PVCz absorption band and CT absorption band, the fluorescence peak in the time-resolved spectra shifted continuously to short wavelength with time. The direction of the shift was opposite to that of the exterplex fluorescence. The dependence of the steady-state CT fluorescence intensity on concentration of the acceptor was also different from the exciplex system. These different behaviours of fluorescence dynamics between the CT and the exciplex systems were discussed from the viewpoint of the overlap of CT and exterplex fluorescence for the CT system and of a morphological change of PVCz films caused by formation of ground-state CT complexes.

Laser ablation dynamics of poly(N-vinylcarbazole) film as revealed by time-resolved fluorescence spectroscopy

Abstract Time-resolved fluorescence spectra of poly (N-vinylcarbazole) films were measured, following laser ablation, by a streak camera system. Two kinds of excimer fluorescence, a broad plasma-like emission, and the emission due to C2 and CN radicals were observed, and their temporal characteristics determined. Ablation dynamics can be interpreted in terms of non-linear photochemical processes, involving S1-S1 annihilation.

Fluorescence characterization of ablated polymeric materials: Poly(methyl methacrylate) doped with 1‐ethylpyrene

Fluorescence spectra and rise as well as decay curves of 1‐ethylpyrene (EPy) in poly(methyl methacrylate) films changed using a XeCl (308‐nm) excimer laser as an ablation source. This phenomenon was observed not only for the ablated area but also for the masked region of about 20 μm around the ablated area and was attributed to the change of the dispersion condition of EPy. Effects of laser ablation upon properties of polymer films were elucidated by analyzing fluorescence dynamics using a microscope and under a total internal reflection condition.

Fluorescence dynamics of poly (N-vinylcarbazole) in fluid solution. Multivariate analysis of time-resolved fluorescence spectra

Abstract Time-resolved fluorescence spectra of poly(N-vinylcarbazole) in solution were analyzed by using a principal multicomponent spectral estimation method. It was clearly indicated that the spectra were composed of only three component fluorescence (monomer, partial overlap excimer, and sandwich excimer). Rise as well as decay curves of this component fluorscence were nonexponential and depended upon tacticity of the polymer. The partial overlap is formed not only by ultrafast trapping in the pre-existing site but also through dynamic processes such as energy migration. In tens of ns time range the excited monomer as well as the partial overlap excimer are produced via dissociation and re-activation of the sandwich excimer