Photoinduced intramolecular electron-transfer processes in [60]fullerene and N,N-bis(biphenyl)aniline molecular systems in solutions

Photoinduced intramolecular charge-separation and charge-recombination processes in covalently connected C-60-(spacer)-bis(biphenyl)aniline (C-60-SP-BBA) and C-60-((spacer)-bis(biphenyl)aniline)(2) (C-60-(sp-BBA)(2)) have been studied by time-resolved fluorescence and transient absorption methods. Since a flexible alkylthioacetoamide chain was employed as the spacer, the folded structures in which the BBA moiety approaches the C-60 moiety were obtained as optimized structures by molecular orbital calculations. The observed low fluorescence intensity and the short fluorescence lifetime of the C-60 moiety of these molecular systems indicated that charge separation takes place via the excited singlet state of the C60 moiety in a quite fast rate and high efficiency even in the nonpolar solvent toluene, which was a quite new observation compared with reported dyads with different spacers. From the absorption bands at 880 and 1000 nm in the nanosecond transient absorption spectra, generations of C-60(center dot-)-sp-BBA(center dot+) and C-60(center dot-)-(sp-BBA(center dot+))(sp-BBA) were confirmed. The rates of charge separation and charge recombination for C-60-(sp-BBA)(2) are faster than those for C-60-sp-BBA, suggesting that one of the BBA moieties approaches the C-60 moiety by pushing another BBA moiety because of the flexible spacers.