Photoinduced Electron Transfer from a Conducting Polymer to Buckminsterfullerene

Evidence for photoinduced electron transfer from the excited state of a conducting polymer onto buckminsterfullerene, C₆₀, is reported. After photo-excitation of the conjugated polymer with light of energy greater than the π-π^* gap, an electron transfer to the C₆₀ molecule is initiated. Photoinduced optical absorption studies demonstrate a different excitation spectrum for the composite as compared to the separate components, consistent with photo-excited charge transfer. A photoinduced electron spin resonance signal exhibits signatures of both the conducting polymer cation and the C₆₀ anion. Because the photoluminescence in the conducting polymer is quenched by interaction with C₆₀, the data imply that charge transfer from the excited state occurs on a picosecond time scale. The charge-separated state in composite films is metastable at low temperatures.