Kinetics of the Decay of Excited Singlet State into a Pair of T-Excitons in Rubrene Films: Mechanism and Manifestation of Exciton Migration

Abstract

The kinetics of the decay (splitting) of the excited singlet -state of rubrene molecules into a pair oftriplet-excitons (T-excitons) in rubrene films, usually represented in terms of the kinetics of the decay of fluorescence(KDF) from the -state, is analyzed in detail. The KDF is known to be significantly controlled bythe process of diffusive migration and annihilation of the generated T-excitons. In the analysis, two migrationmodels are considered: the two-state model (TSM), treating the migration effect as a result of transitionsbetween the [TT] state of coupled T-excitons (at small TT-distances r) and the [T+T]-state of freely migratingЕ-excitons (at large distances r), as well as the free migration model (FMM), neglecting the effect of the [TT]state. Within the TSM and FMM, the expressions for are derived, which are applied to describe the KDF ,measured in amorphous rubrene films. Within the experimentally investigated range of times, , the TSM isshown to reproduce the behavior of the experimental KDF much more accurately than the FMM. At longertimes a substantial difference () between and the FMM-predicted KDF is found, which is far beyond theexperimental error (3%).