Femtosecond time-resolved absorption measurements were performed on a thin film of the conjugated ladder polymer poly(benzimidazobenzophenanthroline) by using a 2-eV (620-nm) pump and a white-light-continuum probe. Transient photoinduced bleaching of the π-${\mathrm{\pi }}^{\mathrm{*}}$ transition accompanied by photoinduced absorption in the optical gap were observed. The photoinduced absorption decays with a fast subpicosecond component and a slow ∼20-ps component. The experimental results are well accounted for by the self-trapped exciton model.

• Received 19 September 1994

DOI:https://doi.org/10.1103/PhysRevB.51.6838