Chromism and luminescence in regioregular poly(3-dodecylthiophene)

We report photoluminescence studies of poly(3-dodecylthiophene) (P3DT) in solution. In a good solvent the polymer exhibits luminescence with a high quantum efficiency and a decay time of 500 ps. In a poor solvent the emission is red shifted with a 20-fold reduction in quantum efficiency and a decay profile that is non-monoexponential, but has an average lifetime that is very similar to the good solvent environment. The data indicate a large increase in the natural radiative lifetime from approximately 1 ns in a good solvent to 20 ns in a poor solvent, which implies an emitting state that is different in the two situations. In the poor solvent the spectrum is almost identical to that of the thin film, suggesting that the polymer aggregates in the solution and the emitting species is the same in both environments. The data are consistent with the formation of an excited state that is not localized on a single chain but is delocalized over more than one chain.