Mechanistic Study of Electron Spin Polarization Transfer in Covalent Donor–Acceptor-Radical Systems

The mechanism of spin polarization transfer from a photogenerated spin-correlated radical pair to a stable radical was studied in a covalent donor-chromophore-acceptor-stable radical (D-C-A-R•) system, where the donor (D) is 4-methoxyaniline (MeOAn), the chromophore (C) is 4-(N-piperidinyl)-naphthalene-1,8-dicarboximide (ANI), the acceptor (A) is naphthalene-1,8:4,5-bis(dicarboximide) (NDI) and the stable radical (R•) is (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). Experiments probed the effect of the spin–spin exchange interaction between D•+ and A•− as well as the charge recombination dynamics of D•+-C-A•− on spin polarization transfer from the D•+-C-A•− SCRP to R• as a function of the dielectric environment in glassy media at cryogenic temperatures. The results show that spin polarization on R• is generated by asymmetry in the charge recombination pathways rather than variations in the spin–spin exchange interaction between D•+ and A•−. These results inform design criteria for using an SCRP to spin polarize a third spin for potential applications in quantum information science.