Photoinduced Charge Separation and Recombination in a Novel Methanofullerene−Triarylamine Dyad Molecule

Intramolecular charge separation (CS) and charge recombination (CR) processes of the dyad molecule linking C60 and N,N-di(6-tert-butylbiphenyl)benzenamine (BBA) were investigated by pico- and nanosecond laser flash photolysis methods. Furthermore, intermolecular electron transfer to a methanofullerene (C61H2) was also investigated; the electron-transfer rate between triplet excited C61H2 and BBA was somewhat slower than that of C60 due to less negative reduction potential of C61H2. As for the BBA−C60 dyad molecule, CS was successfully observed in polar solvents by excitation of C60 moiety with picosecond laser pulse, while only the intersystem crossing was observed in nonpolar solvent. The CS process in the Marcus “normal region” was confirmed. In moderately polar solvent, radical ion pairs recombined within a few nanoseconds to generate the ground state and the triplet excited state of the C60-moiety. On the other hand, in polar solvents, the radical ion pairs decayed by two-steps: Most part decayed within 1 ns, while the radical ions were also observed in the submicrosecond region for a ca. 10% yield of generated BBA•+-C60 •-. An equilibrium between CS and triplet states was proposed for the mechanism of long-lived CS state.