Fluorescence yield and lifetime of isolated polydiacetylene chains: Evidence for a one-dimensional exciton band in a conjugated polymer

The fluorescence lifetime {τ} and quantum yield ηf of isolated red polydiacetylene chains dispersed in their monomer single crystal matrix were measured between 10 and 100 K. {τ} increases up to 120 ps at 40 K, then rapidly decreases at higher T. ηf is a continuously decreasing function of T. The radiative lifetime τᵣ is proportional to √T in the whole T range studied. This is the expected behavior for a purely one-dimensional system without localization, a behavior which is not usually observed even in semiconductor quantum wires. An order of magnitude of the exciton effective mass m*≈0.3 is inferred. The nonradiative lifetime τₙᵣ is constant up to 50 K, then decreases exponentially, indicating the opening of a thermally activated decay channel.