Fluctuating exchange interactions enable quintet multiexciton formation in singlet fission

TL;DR

This paper presents a theoretical model explaining the formation of a quintet multiexciton state during singlet fission, driven by fluctuating exchange interactions, supported by ESR spectrum simulations.

Contribution

It introduces a novel theoretical framework linking time-varying exchange coupling to multiexciton formation in singlet fission.

Findings

Simulated ESR spectra match experimental observations.

Identified conditions for adiabatic and diabatic spin state transitions.

Provided insights into the role of fluctuating exchange interactions.

Abstract

Several recent electron spin resonance studies have observed a quintet multiexciton state during the singlet fission process. Here we provide a general theoretical explanation for the generation of this state by invoking a time-varying exchange coupling between pairs of triplet excitons, and subsequently solving the relevant time-varying spin Hamiltonian for a range of transition times. We simulate experimental ESR spectra and draw qualitative conclusions about the adiabatic/diabatic transition between triplet pair spin states.