PHOTOINDUCED ELECTRON-TRANSFER FROM POLYGERMANE TO C-60 STUDIED BY LASER FLASH-PHOTOLYSIS

Electron transfer from poly(phenylmethylgermylene) (PMePhGe) to photoexcited C-60 in benzene-acetonitrile solution has been investigated by 532 nm laser flash photolysis in the near-IR region. The transient absorption band of the C-60 triplet state (C-3(60)*) appeared immediately after nanosecond laser exposure. With the decay of C-3(60)*, the absorption bands of the radical anion of C-60 (C-60(.-)) and the radical cation of PMePhGe appeared in the region 900-1600 nm. The rate constant of the electron transfer from PMePhGe to C-3(60)* was determined to be 2.33 x 10(8) M(-1) s(-1), which was similar to that for poly(methylphenylsilylene). Electron transfer from the singlet state of C-60 (C-1(60)*) was investigated by fluorescence quenching experiments using a picosecond fluorescence lifetime measurement system, and the quenching rate constant was determined to be 4.00 x 10(10) M(-1) s(-1). The rate constant of intersystem crossing from C-1(60)* to C-3(60)* was determined to be 1.10 x 10(9) s(-1) by picosecond time-resolved absorption spectroscopy using a streak camera. Electron transfer from C-1(60)* to PMePhGe and intersystem crossing from C-1(60)* to C-3(60)* are competitive, and the intersystem crossing is dominant in a dilute solution system. When a 355 nm laser was used as the excitation light, photochemical intermediates were produced from the direct photolysis of PMePhGe in addition to the electron transfer.