Photoinduced intramolecular processes in a tricomponent molecule C 60(>(CN) 2-DPAF), consisting of an electron-accepting methanofullerene moiety (C 60>) covalently bound to an electron-donating diphenyl-aminofluorene (DPAF) unit via a bridging dicyanoethylenyl group [(CN) 2], were investigated in comparison with (CN) 2-DPAF. On the basis of the molecular orbital calculations, the lowest charge-separated state of C 60(>(CN) 2-DPAF) is suggested to be C 60• -(>(CN) 2- DPAF• +) with the negative charge localized on the fullerene cage, while the upper state is C 60(>(CN) 2• --DPAF• +). The excited-state events of C 60(>(CN) 2-DPAF) were monitored by both time-resolved emission and nanosecond transient absorption techniques. In both nonpolar and polar solvents, the excited charge-transfer state decayed mainly through initial energy-transfer process to the C 60 moiety yielding the corresponding 1C 60*, from which charge separation took place leading to the formation of C 60• -(>(CN) 2-DPAF• +) in a fast rate and high efficiency. In addition, multistep charge separation from C 60(>(CN) 2• --DPAF• +) to C 60• -(>(CN) 2-DPAF+) may be possible with the excitation of charge-transfer band. The lifetimes of C 60• -(>(CN) 2-DPAF• +) are longer than the previously reported methanofullerene-diphenylaminofluorene C 60(>(C=O)-DPAF) with the C 60 and DPAF moieties linked by a methanoketo group. These findings suggest an important role of dicyanoethylenyl group as an electron mediating bridge in C 60(>(CN) 2-DPAF).
ASJC Scopus subject areas
- Physical and Theoretical Chemistry