Abstract
The kinetics of the decay (splitting) of the excited singlet -state of rubrene molecules into a pair of
triplet-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 by
the process of diffusive migration and annihilation of the generated T-excitons. In the analysis, two migration
models are considered: the two-state model (TSM), treating the migration effect as a result of transitions
between the [TT] state of coupled T-excitons (at small TT-distances r) and the [T+T]-state of freely migrating
Е-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 is
shown to reproduce the behavior of the experimental KDF much more accurately than the FMM. At longer
times a substantial difference () between and the FMM-predicted KDF is found, which is far beyond the
experimental error (3%).