Anisotropic multiexciton quintet and triplet dynamics in singlet fission via PEANUT

The quintet triplet-pair state generated upon singlet fission is a critical intermediary that dictates the fate of excitons which can be exploited for photovoltaics, information technologies and biomedical imaging. In this report, we demonstrate that continuous wave and pulsed electron spin resonance techniques such as PEANUT, which have emerged as the primary tool for identifying the spin pathways in singlet fission, probe fundamentally different triplet pair species. We directly observe that the generation rate of high-spin triplet pairs is dependent on the molecular orientation with respect to the static magnetic field. Moreover, we demonstrate that this observation can prevent incorrect analysis of cw-ESR measurements, and provide insight into the design of materials to target specific pathways which optimise exciton properties for specific applications.