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

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 -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-(A-R) and D-(A-R). Subsequently, at 140 K, D-(A-R) → D-A-R, whereas D-(A-R) → D-A-R. In contrast, at 105 K, D-(A-R) → D-A-R and D-A-R. Time-resolved EPR spectroscopy shows that D-A-R is highly spin-polarized, where the = ±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.