Singlet fission dynamics modulated by molecular configuration in covalently linked pyrene dimers, Anti- and Syn-1,2-di(pyrenyl)benzene

Abstract

Covalently linked dimers (CLDs) and their structural isomers have attracted much attention as potential materials for improving power conversion efficiencies through singlet fission (SF). Here, we designed and synthesized two covalently ortho-linked pyrene (Py) dimers, anti- and syn-1,2-di(pyrenyl)benzene (Anti-DPyB and Syn-DPyB, respectively), and investigated the effect of molecular configuration on SF dynamics using steady-state and time-resolved spectroscopies. Both Anti-DPyB and Syn-DPyB, which have different Py-stacking configurations, form excimers, which then relax to the correlated triplet pair ((T1T1)) state, indicating the occurrence of SF. Unlike previous studies where the excimer formation inhibited an SF process, the (T1T1)'s of Anti-DPyB and Syn-DPyB are formed through the excimer state. The dissociation of (T1T1)'s to 2T(1) in Anti-DPyB is more favorable than in Syn-DPyB. Our results showcase that the molecular configuration of a CLD plays an important role in SF dynamics. Singlet fission excited-state relaxation, as observed in covalently linked dimers, could allow energy-conversion efficiencies in photovoltaic devices beyond the Shockley-Queisser limit. Here, the authors study the effect of the molecular configuration of two covalently ortho-linked pyrene dimers on singlet fission dynamics using steady-state and time-resolved spectroscopies.