Photoinduced electron transfer between C 60 and carbazole dimer compounds in a polar solvent

Abstract

Photoinduced electron transfer processes between carbazole (Cz) dimer compounds and C 60 in benzonitrile have been investigated by observing the transient absorption spectra in the visible and near-IR regions. By excitation of C 60 with 532 nm-laser light, electron transfer occurred via the triplet excited state of C 60 ( T C 60 ∗ ) from the Cz-dimer compounds, which was confirmed by observing characteristic absorption bands due to C 60 − and the Cz-dimer radical cation. The Cz-dimer compounds, forming sandwich-like conformation of radical cation, showed the charge resonance (CR) bands in the near-IR region longer than 1200 nm. Rate constants for electron transfer seem to depend on the conformation of the Cz-dimer radical cation. The Cz-dimer compounds taking sandwich conformation donate the electron easily to T C 60 ∗ , because of the stabilization energies of the sandwich dimer radical cations of the Cz-dimer compounds. By excitation of the Cz-dimer compounds with 355 nm-laser light, the absorption bands due to the Cz-dimer radical cations appeared immediately after the laser irradiation and the absorption of C 60 − is formed at diffusion controlled rate. This observation suggests that direct photoejection from the Cz-dimer compounds occurs in benzonitrile, yielding the Cz radical cations and solvated electron, in which the latter was trapped with C 60.