Singlet Fission Dynamics Modulated by Molecular Configuration in Covalently Linked Pyrene Dimers, Anti- and Syn-1,2-di(Pyrenyl)Benzene

Abstract

Various covalently linked dimers (CLDs) and their structural isomers have attracted much attention as a potential material to improve the power conversion efficiencies of photovoltaic devices and OLEDs through singlet fission (SF). However, the effect of the molecular configuration on improving the efficiency through the spatial arrangement has not been explored yet. 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), to elucidate the effect of the molecular configuration on SF dynamics. Both Anti-DPyB and Syn-DPyB, which have different Py-stacking configurations, form excimers and then relax to the correlated triplet pair (1(T1T1)) state, indicating the occurrence of SF. Unlike previous studies where the excimer formation inhibited an SF process, the 1(T1T1)’s of Anti-DPyB and Syn-DPyB are formed through the excimer state. The 1(T1T1) of Anti-DPyB dissociates to form free triplets, completing SF, whereas the 1(T1T1) of Syn-DPyB does not undergo dissociation. Our results showcase that the molecular configuration of a CLD plays an important role in SF dynamics, suggesting that the strategic molecular design and its experimental characterization may provide a new route to improving the power conversion efficiency in real devices.