Picosecond Time-Resolved Infrared Absorption Studies on the Photoexcited States of Poly(p-phenylenevinylene)

Picosecond time-resolved infrared absorption spectra of the photoexcited states of poly( p -phenylenevinylene) [( C 6 H 4 CH CH ) n, PPV] have been observed with tunable picosecond light pulses obtained by difference-frequency generation between signal and idler waves from an optical parametric generator and amplifier. The time-resolved photoinduced infrared absorption bands due to a vibrational transition observed at 1550 cm -1 and an electronic transition at 3000 cm -1 of the photoexcited PPV have fast (≈1.7 ps) and slow (≈50 ps) decay components. By comparison of the picosecond time-resolved infrared absorption spectra of short-lived (fast decay component) and long-lived (slow decay component) transient species with the photoinduced and doping-induced infrared difference spectra of PPV, the short-lived transient species is assigned to bound polaron pairs, and the long-lived transient species is assigned to positive and negative polarons.