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 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 ms = ±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.