The effect of excitonic interactions on singlet fission dynamics in crystalline tetracene

Singlet fission in organic semiconductors is interesting for its potential application in boosting the efficiency of solar conversion. Singlet-singlet annihilation induced by excitonic interaction has been regarded as a process that competes against singlet fission in high-density regime. In this work, we conduct a systematic transient optical study to investigate the density-dependent singlet fission dynamics in crystalline tetracene. Surprisingly, the transient absorption data indicate the rate of singlet fission is actually increased with increasing the excitation density [1], which is further supported by probing the quantum beating between the manifold states of triplet pairs following Burdett's approach. Our result suggests it is necessary to re-examine the role of excitonic interactions to uncover the physical mechanism underlying singlet fission in crystalline tetracene. [1] Zhang et al., J. Phys. Chem. Lett. 5, 3462 (2014). [2] Burdett {\&} Bardeen, J. Am. Chem. Soc. 134, 8597(2012).