Photoinduced electron-transfer reactions of C60 and p-substituted anilines

Abstract

Photoinduced electron transfers between triplet excited state of C60 (TC60*) and p-substituted anilines in polar solvents [benzonitrile, benzonitrile–benzene (1+2) and o-dichlorobenzene] were investigated using laser flash photolysis by observing transient absorption spectra in the visible and near-IR regions. All anilines donated electrons to TC60*, generating the radical anion of C60 and radical cations of anilines. Quenching rate constants of TC60* (kqT) and quantum yields (ΦetT) for electron transfer viaTC60* were determined; the ΦetT values increased with increases in the kqT values. In highly polar solvents, the ΦetT values were larger than those in less polar solvents, suggesting fast dissociation of the triplet exciplex to an ion pair in polar solvents. Rate constants for the electron transfer (ket) in polar solvents followed Rehm–Weller relationship, whereas only a poor correlation was obtained in less polar solvents. The linear relationship between the ket values and Hammett substituent constants showed a negative slope indicating high electrophilicity of TC60*. In the Hammett plot of the ΦetT values, the slope in polar solvents was more negative than that in less polar solvents, suggesting that the transition state of the electron transfer becomes polar with increase in solvent polarity. In the case of the photoinduced reaction of p-ethynyl- or p-ethenylaniline, C60 adduct formation was confirmed in addition to oligomerization of these anilines.