Fluorescence decay curves and time-resolved spectra of poly(N-epoxypropylcarbazole), PEPCA, at room temperature and at 11 K

Summary

Time-resolved fluorescence spectra of solid films of low-molecular-weight poly(N-epoxypropylcarbazole), PEPCA, measured at room temperature and at 11 K are reported. The spectra reveal the presence of two types of emitting centra in the polymer. Below 400 nm, noninteracting carbazolyl side groups emit fluorescence typical of the monomer unit. Above 400 nm, structured emission with peaks at 410, 430, and 460 nm has been observed. Comparison of the detected spectra with that of crystalline N-isopropylcarbazole together with other evidence supports strongly the suggestion that the latter emission is due to intermolecular arrays of the side groups arranged in such a way that their molecular planes are parallel or nearly parallel to each other with antiparallel orientation of the short in-plane molecular axes of the nearest neighbours. The time-resolved spectra and the decay curves show that excitation energy is transfered from monomer side groups to those built in the crystallike arrays and that this transfer becomes less effective at low temperatures.