Manifestation of T-exciton migration in the kinetics of singlet fission in organic semiconductors

Singlet fission (SF) in organic semiconductors, i.e. spontaneous splitting of the excited singlet (S-1) state into triplet (T) exciton pair, is known to be strongly influenced by back annihilation of TT-pair. We show that this influence is properly described only by taking into account diffusive exciton migration (EM). Within the model of two states (states of interacting TT-pairs and migrating excitons) the SF is studied by analyzing the kinetics I-s1(t) of decay of fluorescence from S-1-state. Analysis shows that the EM strongly manifests itself in the kinetics resulting, in particular, in long-time dependence Is(1)(t) similar to t-(3/2). The model accurately describes Is(1)(t), recently observed for a number of semiconductors. (C) 2017 Elsevier B.V. All rights reserved.