Photoinduced electron transfer and its magnetic field dependence in supramolecular complex of zinc(II) tetraphenylporphyrin–viologen chain-linked compound with 2,3,6-tri-O-methyl-β-cyclodextrin

Photoinduced electron transfer in a supramolecular complex of zinc(II) tetraphenylporphyrin–viologen covalently linked compound (ZnP–V2+) with 2,3,6-tri-O-methyl-β-cyclodextrin in acetonitrile–water (1:1, v/v) was investigated. On increasing the magnetic fields, the lifetime of photogenerated biradical (ZnP+–V+) increased and reached an asymptotic value under high magnetic fields (>100 mT). The effects were explained by the electron-nuclear hyperfine coupling and spin–lattice relaxation mechanisms. The observed forward electron transfer was quite slow compared with the free ZnP–V2+, and was increased by the magnetic fields. These results were explained by the fact that the photoinduced electron transfer was an equilibrium between the 3ZnP*–V2+ and ZnP+–V+, and this free energy change was quite a small value (ca. −1.3 kJ/mol).