| Research Abstract |
(1) By conducting systematic studies on the energy gap dependence of CR (charge recombination) rate of geminate IP (ion pair) produced by CS (charge separation) at encounter between fluorescer and quencher in acetonitrile with ultrafast laser spectroscopy, we have given experimental proof of the bell-shaped energy gap dependence of the CR rate of IP for the first time. (2) By examining the interrelations proposed previously for the fact that no inverted region was observed for the CS reaction, we have, proved that the lack of inverted effect up to the -DELTAG^ﾟ_ = 1.63 eV is intrinsic property of such fluroescer-quencher systems. (3) Since the fluorescence quenching rate constant obtained by stationary measurements is diffusion-limited, we determined true CS rate constants for the region -DELTAG^ﾟ_ = 0-2 eV by examining the transient effect in the fluorescence decay curve. However, such bell-shaped energy gap dependence as expected from the Marcus theory was not observed. (4) These res
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ults can be interpreted by our theory taking into account nonlinear polarization of solvent around charged solute and distribution of electron transfer distance on the energy gap dependence of CS rate constant and also CR rate of IP. (5) Femtosecond- picosecorid laser photolysis studies on the photoinduced CS in some strongly interacting donor acceptor systems directly combined by single bond and some CT complexes showed rather slow CS process and energy gap dependence of CR of produced IP in the CT complexes was quite different from bell-shape, which can not be interpreted by conventional electron transfer theories. (6) Other ultrafast laser photolysis studies were made on photosynthetic model systems, monoptiotonic electron ejection from vibrationally nonrelaxed S_1 of aromatic amines in polar solvents, dynamics of cation-electron pair produced by multiphoton ionization in nonpolar solvents, hydrogen transfer reaction of excited benzophenone-amine systems, etc., which contributed greatly to the elucidation of reaction mechanisms. Less
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