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.