Molecular Control of Spin-Entangled Triplet Excitons from Singlet Fission

The chemical versatility and controllable functionalization of molecular architectures make them strong candidates as platforms for quantum information science (QIS). Recent work has aimed to tailor molecular systems that harbor electron spins on transition metals for light-driven spin polarization at room temperature and optical readout, inspired by archetypal solid-state qubits. Radical pair spins born from photoinduced charge transfer in molecular complexes represent an alternative approach.1 The unique photophysics of purely organic systems, particularly in the acene class of fused polycyclic aromatic compounds, provide particular appeal, however the inherent properties of candidate spin states with respect to molecular structure and relevant physical parameters are poorly understood. The overall goal of the proposed work is to pursue a detailed mechanistic answer to how molecular structure and intermolecular geometry dictate triplet-pair spin state behavior. Triplet pairs generated from the singlet fission process possess assets not found in other spin systems, including the juxtaposition and entanglement of two excited state spin-1 particles driven by ultrafast photo-initiation and the associated couplings that form the spin state manifold. How can we use chemistry, including chromophore selection and peripheral functionalization, to tune this triplet-pair spin state manifold and its population flow, and do intrinsic advantages for QIS emerge? We bring long-standing experience and expertise in rationally making, assembling, and characterizing functional singlet fission molecules and will use guidance from recent compelling results to test important notions of photogenerated triplet pair spin polarization and its relaxation.2 Figure 1.