The Manifestation of Spin-Selectivity of the Singlet Exciton Decay into a Pair of Triplets in the Kinetics of the Exciton Decay in Rubrene Films

The kinetics of singlet fission (SF) (i.e., spontaneous splitting of the excited singlet state into a pair of triplet (T) excitons (TT-pair)) is known to be significantly affected by TT-annihilation (TTA), which manifests itself in magnetic field effects on the TTA and, in particular, in the magnetic-field dependence of the SF-kinetics. In this study, in the two-state model (TSM), a method is proposed for treating the magnetic field effects on the SF-kinetics, which allows for the correct description of the manifestation of the stochastic migration of T-excitons assuming that the manifestation results from the transition from two states of coupled and freely diffusing T-excitons. In the TSM, the analytical expression for the magnetic-field-dependent part of the SF-kinetics is derived. This expression is applied to the analysis of the SF-kinetics measured in amorphous rubrene films in the absence of a magnetic field and in the field B = 8 kGs.