Nanosecond time-resolved photoinduced absorption of trans-polyacetylene

The photoinduced absorption and bleaching of trans-polyacetylene were investigated in nanosecond time regime for the first time. 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 saturates at ΔA/A_{O ∼ 0.01}. The decay curves of transient absorbance change can be fitted to erf[(t/τ)^{- 1 2}]. The time constants are 144±15 ns ((CH)_x) and 305±27 ns ((CD)_x) at 4 K and 32±6 ns ((CH)_x) and 40±6 ns ((CD)_x) at 290 K. When the trans content in cis-rich film decreases, the time constant becomes longer. The decay kinetics was interpreted by the interchain recombination of photoexcited polaron pairs.