Photoinduced charge separation of the covalently linked fullerene-triphenylamine-fullerene triad. effect of dual fullerenes on lifetimes of charge-separated states

Article abstract of DOI:10.1246/bcsj.80.2465

Photoinduced intramolecular events of the newly synthesized fullerene-triphenylamine-fullerene (C₆₀-TPA-C₆₀) triad, in which the TPA entity was substituted with an electron-donating CH ₃O-group to increase electron-donating ability, were investigated in relation to a C₆₀-TPA dyad. The molecular orbital calculations showed that the radical cation is located on the TPA entity, whereas the radical anion is located on two C₆₀ entities in the radical ion pair. The fluorescence intensity of the singlet excited state of C₆₀ was efficiently quenched by the attached TPA moiety in polar solvents. The quenching pathway involves a charge-separation process from the TPA to the singlet excited state C₆₀. The lifetimes of the radical ion-pairs for C ₆₀-TPA-C₆₀ evaluated from nanosecond transient absorption measurements were found to be 600 and 454 ns in benzonitrile and dimethylformamide, respectively. These lifetimes of radical ion-pairs of C ₆₀-TPA-C₆₀ are longer than those of the C₆₀-TPA dyad, which reflects the effect of the second C₆₀ moiety in stabilizing the radical ion-pairs.