INFRARED PHOTOEXCITATION SPECTROSCOPY OF CONDUCTING POLYMER AND C-60 COMPOSITES - DIRECT EVIDENCE OF PHOTOINDUCED ELECTRON-TRANSFER

We report direct spectral evidence of photoinduced electron transfer from the excited state of conducting polymer onto C-60 by infrared photoexcitation spectroscopy, from 0.01 eV (100 cm(-1)) to 1.3 eV (11,000 cm(-1)). The photoinduced absorption spectra of poly(3-octylthiophene) (P3OT) and poly[2-methoxy, 5-(2'ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) are characterized by subgap electronic absorptions and associated infrared-active vibrational modes. Upon adding a few percent of C-60 into both conducting polymers, the photoinduced absorption spectra are significantly enhanced in magnitude and two new peaks are found at 1.15 eV and 1.25 eV. The photoinduced charge transfer from conducting polymer onto C-60 enhances the quantum efficiency for photogeneration of charge carriers, resulting in the enhanced photoinduced response of conducting polymer and the appearance of 1.15 eV and 1.25 eV signatures associated with C-60(-).