Photoinduced Electron Transfer from Polygermane to C₆₀Studied by Laser Flash Photolysis

Electron transfer from poly(phenylmethylgermylene) (PMePhGe) to photoexcited C₆₀in benzene—acetonitrile solution has been investigated by 532 nm laser flash photolysis in the near-IR region. The transient absorption band of the C₆₀triplet state (³C₆₀*) appeared immediately after nanosecond laser exposure. With the decay of ³C₆₀*, the absorption bands of the radical anion of C₆₀(C₆₀ ^•-) and the radical cation of PMePhGe appeared in the region 900-1600 nm. The rate constant of the electron transfer from PMePhGe to ³C₆₀* was determined to be 2.33 × 10⁸ M^-1 s^-1, which was similar to that for poly(methylphenylsilylene). Electron transfer from the singlet state of C₆₀(¹C₆₀*) was investigated by fluorescence quenching experiments using a picosecond fluorescence lifetime measurement system, and the quenching rate constant was determined to be 4.00 × 10¹⁰ M^-1 s^-1. The rate constant of intersystem crossing from ¹C₆₀* to ³C₆₀* was determined to be 1.10 × 10⁹ s^-1 by picosecond time-resolved absorption spectroscopy using a streak camera. Electron transfer from ¹C₆₀* to PMePhGe and intersystem crossing from ¹C₆₀* to ³C₆₀* 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.