Electronic excitation energy transfer in poly-N-epoxypropyl-3,6-dibromocarbazole

Abstract

The mechanisms of electronic excitation energy transfer in films of poly-N-epoxypropyl-3,6-dibromocarbazole doped with pyrene, rubrene, and bis[2-(2′-benzothienyl)-pyridinato-N,C3′](acetylacetonate)iridium(III) (Btp2Ir(acac)) have been studied in the range T = 5–295 K. It has been established that the mechanisms of transfer depend on the relative position of the S1 and T1 levels of the base and dopant: if the S1 level of the dopant lies between the S1 and T1 levels of the base and its T1 level is below than that of the base (pyrene molecules), only the triplet-triplet transfer takes place, whereas if the S1 level of the dopant lies below the T1 level of the base (pyrene and Btp2Ir(acac) molecules), the triplet-singlet transfer is observed in addition to the triplet-triplet transfer. It has been assumed that the spin-forbidden triplet-singlet energy transfer is allowed because of the strong spinorbit interaction induced by two heavy bromine atoms in chromophores of the polymer. This transfer proceeds through the long-range dipole-dipole interaction at low temperatures and the electron exchange interaction in the vicinity of room temperature.