Ultrafast Spectroscopic Study of Photoinduced Electron Transfer in an Oligo(thienylenevinylene):Fullerene Composite

Photoinduced electron transfer and competing processes have been studied in composites of an oligo(thienylenevinylene) (OTV), comprised of ten dibuthoxyl‐thiophene units separated by vinylene units, and a C 60 derivative, [6,6]‐phenyl‐C 61 butyric acid methyl ester (PCBM), by using femtosecond transient absorption spectroscopy and sub‐nanosecond transient photoconductivity. We find that in OTV:PCBM the photoexcitations decay primarily via intrachain relaxation rather than photoinduced electron transfer from OTV to PCBM. The electron‐transfer process requires ca. 14 ps; larger by more than two orders of magnitude than the required time observed in conjugated‐polymer:C 60 composites, and also larger than the 0.6 ps singlet‐state lifetime in OTV. These observations indicate that the quantum efficiency for photoinduced electron transfer in OTV:PCBM is less than 5 %.