Switching intramolecular singlet fission in tetracene dimers via subtle changes in bridges

Abstract

Singlet fission has attracted great attention in recent years owing to the potential of enhancing photoenergy conversion efficiency through exciton multiplication. Herein, we designed tetracene dimers bridged by two regio-isomers, namely 2T-DPP and 2T-DOP, in which 2T-DPP has a C₂ symmetry, while 2T-DOP is asymmetric. Femtosecond transient absorption spectroscopy reveals that 2T-DPP undergoes singlet fission with a triplet yield of 125% in dichloromethane. In contrast, 2T-DOP undergoes no singlet fission. Theoretical investigation indicates that 2T-DPP features a delocalized exciton, whereas localized exciton resides in the dimer 2T-DOP due to low symmetry. This work demonstrates that subtle changes in the bridge structure could significantly alter the efficiency of intramolecular singlet fission and highlights the importance of molecular symmetry in modulating the exciton delocalization and thus in switching intramolecular singlet fission.