PHOTOEXCITATIONS IN POLYCARBAZOLYLDIACETYLENES

We present the results of a photoinduced-absorption study carried out on an unsymmetrical polydiacetylene having a carbazolyl group directly bound to the acetylene moiety, i.e., poly-1(-N-carbazolyl)penta-1,3-d iyn-5-acetoxy (polyCPDA). The absorption spectrum of microcrystalline samples in a KBr pellet shows a broad maximum at almost-equal-to 2.2 e V. Photoexcitation of these samples at 2.54 eV gives rise to a lumines cence emission from 1.4 to 2 eV with a maximum at almost-equal-to 1.8 eV and two well-resolved photoinduced-absorption (PA) peaks at almost- equal-to 0.45 and almost-equal-to 1.1 eV. From the temperature, laser intensity, and chopper frequency dependence of the PA signals, we demo nstrate that the dominant long-lived photocarriers are charged bipolar ons formed by interchain charge separation. The lifetimes of the bipol arons in polyCPDA have been found of the order of seconds at 80 K. The intermolecular nature of the observed PA bands appears to be confined by the absence of any photoinduced signal in a solution of oligomers of the same polydiacetylene.