Plenty of Room on the Top: Pathways and Spectroscopic Signatures of Singlet Fission from Upper Singlet States

We investigate dynamic signatures of the singlet fission (SF) process triggered by the excitation of a molecular system to an upper singlet state SN (N > 1) and develop a computational methodology for the simulation of nonlinear spectroscopic signals revealing the SN → TT1 SF in real time. We demonstrate that SF can proceed directly from the upper state SN, bypassing the lowest excited state, S1. We determine the main SN → TT1 reaction pathways and show by computer simulation and spectroscopic measurements that the SN-initiated SF can be faster and more efficient than the traditionally studied S1 → TT1 SF. We claim that the SN → TT1 SF offers novel promising opportunities for engineering SF systems and enhancing SF yields. Ministry of Education (MOE) Submitted/Accepted version L.C. was supported by the Key Research Project of Zhejiang Lab (2021PE0AC02). L.M. was supported by the National Natural Science Foundation of China (Grant 11874125). Y.Z. gratefully acknowledges the support of the Singapore Ministry of Education Academic Research Fund (Grants RG190/18 and RG87/20). G.G.G.’s research was funded by a DUT startup grant and by the National Natural Science Foundation of China (Grant 22088102). W.N. and M.F.G. acknowledge support of Hangzhou Dianzi University through startup funding