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

Abstract

The fluorescence lifetime \ensuremath{\tau} and quantum yield ${\ensuremath{\eta}}_{\mathrm{f}}$ of isolated red polydiacetylene chains dispersed in their monomer single crystal matrix were measured between 10 and 100 K. \ensuremath{\tau} increases up to 120 ps at 40 K, then rapidly decreases at higher T. ${\ensuremath{\eta}}_{f}$ is a continuously decreasing function of T. The radiative lifetime ${\ensuremath{\tau}}_{\mathrm{r}}$ is proportional to $\sqrt{T}$ 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 ${m}^{*}\ensuremath{\approx}0.3$ is inferred. The nonradiative lifetime ${\ensuremath{\tau}}_{\mathrm{nr}}$ is constant up to 50 K, then decreases exponentially, indicating the opening of a thermally activated decay channel.