Photoinduced Charge Separation of the Covalently Linked Fullerene–Triphenylamine–Fullerene Triad. Effect of Dual Fullerenes on Lifetimes of Charge-Separated States

Abstract

Abstract 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 CH3O-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 C60–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 C60–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.