Diverse Quantum Interference Regime in Intramolecular Singlet Fission Chromophores with Thiophene-Based Linkers

An array of thiophene-based π-conjugated linkers in covalently-linked pentacene dimers allows us to access diverse quantum interference (QI), modulating nonadiabatic coupling (NAC) in singlet fission (SF) process. Simulations show that structural isomerism in terms of S atom orientation substantially alters NAC with relatively marginal impacts on energies. Extended curly arrow rules (ECARs) reveal sensitive dependence of QI on SF linker topologies and connectivity, categorizing regimes of constructive, destructive, and previously unrealized in SF research, suppressed destructive QI. Drastic NAC changes in terms of S atom orientation are rationalized based on the nature of QI. Our results from nonequilibrium Green’s function calculation using density functional theory corroborates the classification of QI regimes based on ECARs. Moreover, we found that the extent of charge resonance contribution in electronic states relevant to multiexciton formation and the appearance of optically allowed charge transfer excitation strongly depends on the operative QI regime. Notably, the magnitude of NAC effectively captures this influence. Our findings show that QI can rationalize and semi-quantitatively correlate to NAC for multiexciton formation step in SF process.