Controlling the Dynamics of Three Electron Spin Qubits in a Donor-Acceptor-Radical Molecule Using Dielectric...

Photogenerated entangled electron spin pairs provide a versatile source of molecular qubits. Here, we examine the spin-dependent dynamics of a covalent donor-acceptor-radical molecule, D-A-R^•, where the donor chromophore (D) is peri-xanthenoxanthene (PXX), the acceptor (A) is pyromellitimide (PI), and the radical (R^•) is α,γ-bisdiphenylene-β-phenylallyl (BDPA). Selective photoexcitation of D within D-A-R^• in butyronitrile/propionitrile at 140 K and butyronitrile at 105 K results in the spin-selective reactions D-A-R^• → D^•+-¹(A^•--R^•) and D^•+-³(A^•--R^•). Subsequently, at 140 K, D^•+-¹(A^•--R^•) → D^•+-A-R^-, whereas D^•+-³(A^•--R^•) → D-A-R^•. In contrast, at 105 K, D^•+-³(A^•--R^•) → ^3*D-A-R^• and D-A-R^•. Time-resolved EPR spectroscopy shows that ^3*D-A-R^• is highly spin-polarized, where the m_s = ±1/2 spin sublevels of the doublet-quartet manifolds are selectively populated. These results demonstrate dielectric environment control over different spin states in the same molecule.