Ultrafast high-energy luminescence in a high-electron-affinity conjugated polymer

Results are presented of time-resolved-photoluminescence studies of both films and solutions of a cyano-substituted derivative of poly(p-phenylenevinylene) with high electron affinity. For the polymer film a luminescence transient is observed at high energy (2.35 eV) which has a lifetime of 6+/-1 ps and is not seen in continuous-wave (cw) measurements. A long-lived (>2 ns) low-energy transition which corresponds to the peak seen in cw measurements is also seen. These results differ greatly from those obtained from a solution of the polymer where only a single luminescence peak is observed. It is shown that the high-energy transition can be explained either by the radiative decay of an interchain excitation or, after comparison with results obtained on a model oligomer of the polymer, by the radiative decay of an intrachain exciton on short-conjugated chain segments. The low-energy transition is attributed to the decay of an interchain excitation.