Photochemical reactions of triplet state of safranine-T studied by transient absorption spectroscopy in visibleear-IR regions

摘要

Properties and reactivities of the triplet state of safranine-T [~3(STH~+)~*] have been studied by following the transient absorption bands measured with nanosecond laser flash photolysis. Solvent effect was found in the lifetime and T-T annihilation rate constant (k_(TT)) of ~3(STH~+)~*; the lifetime in ethanol is quite long and k_(TT) in water is too small to observe. For electron transfer of ~3(STH~+)~* with various electron donors, the reaction rate constants decrease with the oxidation potentials of the donors along with the Rehem-Weller relation. For the high electron-donors, the reaction rate constants were found to be solvent viscosity dependent rather than dielectric constants, suggesting the triplet exciplex formation prior to electron transfer. Different reactivities of ~3(STH~+)~* towards H-abstraction reactions have been observed depending on the nature of H-atom donors: with phenols, the reaction center of the triplet states has a highly electrophilic nature, while it has a nucleophilic character with respect to thiophenols, suggesting that the reactive position of ~3(STH~+)~* changes with the substr