LONG-LIVED PHOTOEXCITED STATES IN POLYDIACETYLENES - THE PHOTOINDUCED-ABSORPTION SPECTRA OF PDA-4BCMU

We report the results of steady-state photoinduced absorption experime nts on PDA-4BCMU grown on silica substrate. We observe three photoindu ced absorption bands at 0.82, 0.95, and 1.39 eV whose relaxation dynam ics are identical for the two low-energy peaks but different for the 1 .39-eV band. On the basis of the spectra, the pump intensity, modulati on frequency, and signal phase dependences we conclude that the 0.82 a nd 0.95-eV absorption features are due to charged states while the 1.3 9-eV-peak is originated by triplet excitons. The photogeneration of bo th charged and neutral states in PDA-4BCMU as previously observed in p olycarbazolyldiacetylenes indicates that this is a general feature of polydiacetylenes. The relative weight of one excited species over the other one is influenced by the molecular and supramolecular organizati on of the polymer.