화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.110, No.10, 3471-3479, 2006
Effects of extension or prevention of pi-conjugation on photoinduced electron transfer processes of ferrocene-oligothiophene-fullerene triads
Photoinduced electron-transfer processes of alkyl-inserted ferrocene-trimethylene-oligothiophene-fullerene (Fc-tm-nT-C-60) 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 (1)nT* to C-60 for both triads, without forming the charge-separated (CS) state. In polar solvent, the initial CS state, Fc-tm-nT(center dot)-C-60(center dot-), was formed via Fc-tm-nV(1)C(60)* after the EN process from (1)nT* by photoexcitation of the nT moiety and after direct photoexcitation of the C-60 moiety. For Fc-tm-nT(center dot+)-C60(center dot-), the positive charge shifted from the nT(center dot+) moiety to the Fc moiety, producing the final CS state, Fc(center dot+)-tm-nT-C60(center dot-), 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)(center dot+)-C60(center dot-)), was formed immediately after direct photoexcitation of the nT and C60 moieties. The lifetimes of (Fc-nT)(center dot+)-C60(center dot-) were estimated to be 0.1-50 ns by changing nT from 4T to 12T. The longer lifetimes of Fc(center dot+)-tm-nT-C-60(center dot-) than those of (Fc-nT)(center dot+)-C60(center dot-) are caused by the insertion of the trimethylene chain to prevent the pi-conjugation between the Fe and nT moieties. The lifetimes for Fc(center dot+)-tm-nT-C-60(center dot-) and (Fc-nT)(center dot+)-C-60(center dot-) are prolonged by changing nT from 4T to 12T. For the charge-recomb in atom process of Fc(center dot+)-tm-nT-C-60(center dot-), the damping factor was evaluated to be 0.10 angstrom(-1). For (Fc-nT)(center dot+)-C60(center dot-), the oxidation potentials of the nT moieties control the electron-transfer process with reflecting stabilization of the radical cations of the nT moieties.