The Role of Quantum Interference in Intramolecular Singlet Fission

Quantum interference (QI), the constructive or destructive interference of conduction pathways through molecular orbitals, plays a fundamental role in enhancing or suppressing charge and spin transport in organic molecular electronics. Graphical models have been developed to predict constructive versus destructive interference in polyaromatic hydrocarbons, and have successfully estimated the large conductivity differences observed in single-molecule transport measurements. A major challenge lies in extending these models to excitonic (photoexcited) processes, which typically involve distinct orbitals with different symmetries. Here, we investigate how QI models can be applied as bridging moieties in intramolecular singlet fission (iSF) compounds to predict relative rates of triplet pair formation. In a series of bridged iSF dimers, we find that destructive QI always leads to slower triplet pair formation across different bridge lengths and geometries. A combined experimental and theoretical approach reveals the critical considerations of bridge topology and frontier molecular orbital energies in applying QI conductance principles to predict rates of multiexciton generation.