Quintet formation and exchange fluctuations: The role of stochastic resonance in singlet fission

Abstract

Singlet fission describes the spin-conserving production of two triplet excitons from one singlet exciton. The existence of a spin-2 (quintet) triplet-pair state as a product of singlet fission is well established in the literature, and control of quintet formation is an important step towards applying singlet fission in photovoltaics and quantum information. However, a definitive mechanism for quintet formation is yet to be established, which makes it difficult to design materials for optimal quintet formation. Here we outline a mechanism in which inter-triplet exchange coupling fluctuations drive fast and efficient quintet formation. In contrast with conventional wisdom, we show that quintet population can arise despite strong exchange coupling. We evaluate the performance of this quintet formation mechanism in two regimes of conformational freedom, and relate quintet dynamics to material properties of singlet fission molecules.

Spin-dependent recombination mechanisms for quintet bi-excitons generated through singlet fission

“…One possible assumption to obtain a spin-dependent generation/recombination mechanism based on this selection rule is to assume that the exchange energy changes during the generation/recombination events vanishing at some point in time, for example for separated triplets for which the matrix elements | n|S | become non-zero [72]. It was also proposed that stochastic fluctuations of the exchange energy could also induce resonances enabling intersystem crossing [73]. Here we decided to consider a simpler model, based on the mixing between quintet and singlet states due to the zero-field fine structure tensor of the triplet excitons.…”