ULTRAFAST SPECTROSCOPIC STUDIES OF PHOTOINDUCED ELECTRON-TRANSFER FROM SEMICONDUCTING POLYMERS TO C-60

Using femtosecond time-resolved photoinduced absorption spectroscopy, we have studied the dynamics of photoinduced electron transfer from semiconducting polymers to C60. We find that with C60 in poly[2-methoxy-5-(2-ethyl-hexyloxy)-p- phenylene vinylene)], poly(2,5-bis(cholestanoxy)-1,4-phenylene vinylene), and poly(3-octylthiophene) (P3OT), ultrafast photoinduced electron transfer occurs from the * band of the semiconducting polymer to the lowest unoccupied molecular-orbital level of C60. Time-resolved measurements of the dichroic ratio place a 300-fs upper limit on the electron transfer time. The charge-separated state is rendered metastable due to the spatial separation of the electron and hole and to polaron formation associated with the electron on the C60 and the hole on the semiconducting polymer. Increasing the C60 concentration in P3OT increases the lifetime of the charge-separated state. The two p-phenylene vinylene derivatives also displayed metastable charge separation. © 1994 The American Physical Society.