Nanosecond Time-Resolved Photoinduced Absorption of trans-Polyacetylene

Abstract

The photoinduced absorption and bleaching of trans-(CH)_x and trans-(CD)_x in the nanosecond time region were investigated for the first time by time-resolved absorption spectroscopy. The transient absorption near the band gap and the bleaching of the interband transition were observed for both trans-(CH)_x and trans-(CD)_x. The absorption near the band gap saturated at ΔA⁄A₀∼0.01. The decay of transient absorption at 4 K was fitted to \erf [(t⁄τ)^−1⁄2] with τ=144±15 ns for trans-(CD)_x and τ=305±27 ns for trans-(CD)_x. When the temperature is increased, the decay kinetics are given by the same function with shorter time constants, τ=32±6 ns for trans-(CH)_x and τ=40±6 ns for trans-(CD)_x at 290 K. When the trans content in cis-rich film decreased, the time constant became longer. The decay kinetics is interpreted by interchain recombination of photoinduced polaron pairs.