Influence of macromolecule main chain structure on electron excitation energy transfer in carbazole-containing polymers

Efficiencies of energy transfer from singlet excitons to rubrene in poly-N-epoxypropylcarbazole (PEPC) and from triplet excitons to pyrene in poly-N-vinylcarbazole (PVC) were found to increase on heating from 5 to 295 K. At the same time, the transfer efficiency in PVC at rubrene concentration 2∙10^–3 M decreased in the range T = 100–295 K, which correlated with a rise in the intensity of the fluorescence band of the matrix sandwich-like excimers. However, the transfer efficiency increased upon increasing the concentration, which caused the maximum donor–acceptor distance to approach the critical radius of the Forster model. The observed effects were explained by the fact that the free-path lengths of singlet excitons in PEPC and triplet excitons in PVC increased with increasing temperature and, correspondingly, the probability of them approaching the acceptor within distances where energy transfer was possible increased. Singlet-exciton self-trapping at excimer-forming sites and formation of sandwich-like excimers competed in PVC with energy transfer to rubrene.