Photoinduced Electron-Transfer Processes of Fullerene (C_(60)) with Amine Donors:Excited Triplet Route vs Excited Singlet Route

摘要

Dynamic quenching processes of the excited states of C_(60) with amine donors have been studied by changing donor strength,donor concentration,and solvent polarity using steady-state and transient absorption and fluorescence spectro-scopic techniques.Fluorescence quenching of C_(60) by amines was observed,which suggests a dynamic quenching process via the excited singlet state of C_(60) (~1C_(60)~*) in polar and nonpolar solvents.In polar solvents,electron transfer via the excited triplet state of C_(60) (~3C_(60)~*) producing radical ions (C_(60)~(centre dot-) and amine~(centre dot+)) was observed by the nanosecond laser flash photolysis (ca.6 ns laser pulse).When the donor concentrations are below 10-20 mmoldm~(-3),the concentrations of the radical ions increased with the donor concentrations.With further increase of the concentrations of the donors up to 100 mmoldm~(-3),on the other hand,the yields of the radical ions generated via ~3C_(60)~* decreased.These findings indicate that dynamic quenching of ~1C_(60)~* by amines increases with donor concentrations,resulting in a decrease of the intersystem crossing path to ~3C_(60)~*;thus,the yields of the radical ions generated via ~3C_(60)~* decreased even in the highly polar solvent.This implies that the radical ions generated by the dynamic quenching of ~1C_(60)~* may be quite short-lived,even in polar solvents,compared with the radical ions via ~3C_(60)~*.