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.

Automated summary

In this study, we investigate the dynamic signatures of singlet fission (SF) process and develop a computational methodology to simulate the nonlinear spectroscopic signals in real time. We demonstrate that SF can occur directly from an upper singlet state SN, bypassing the lowest excited state, S1. By computer simulation and spectroscopic measurements, we determine the main reaction pathways of SN-initiated SF and find that it can be faster and more efficient than the traditionally studied S1-initiated SF. Therefore, we propose that the SN-initiated SF offers promising opportunities for engineering SF systems and enhancing SF yields.