Photoinduced electron-transfer processes of alkyl-inserted ferrocene - trimethylene - oligothiophene - fullerene (Fc-tm-nT-C60) linked triads and directly linked ferrocene - oligothiophene - fullerene(Fc-nT-C 60) triads were investigated using time-resolved fluorescence and transient absorption spectroscopic methods. In nonpolar solvent, the energy-transfer (EN) process occurred from 1nT* to C 60 for both triads, without forming the charge-separated (CS) state. In polar solvent, the initial CS state, Fc-tm-nT•+-C 60•-, was formed via Fc-tm-nT-1C 60* after the EN process from 1nT* by photoexcitation of the nT moiety and after direct photoexcitation of the C 60 moiety. For Fc-tm-nT•+-C60 •-, the positive charge shifted from the nT•+ moiety to the Fc moiety, producing the final CS state, Fc•+-tm- nT-C60•-, which lasted for 22-330 ns by changing nT from 4T to 12T. For Fc-nT-C60 in polar solvent, the CS state, in which the radical cation is delocalized on both Fc and nT moieties ((Fc-nT) •+-C60•-), was formed immediately after direct photoexcitation of the nT and C60 moieties. The lifetimes of (Fc-nT)•+-C60•- were estimated to be 0.1-50 ns by changing nT from 4T to 12T. The longer lifetimes of Fc•+-tm-nT-C60•- than those of (Fc-nT)•+-C60•- are caused by the insertion of the trimethylene chain to prevent the π-conjugation between the Fc and nT moieties. The lifetimes for Fc•+-tm-nT-C 60•- and (Fc-nT)•+-C 60•- are prolonged by changing nT from 4T to 12T. For the charge-recombination process of Fc•+-tm-nT-C 60•-, the damping factor was evaluated to be 0.10 Å-1. For (Fc-nT)•+-C60 •-, the oxidation potentials of the nT moieties control the electron-transfer process with reflecting stabilization of the radical cations of the nT moieties.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry