Photoinduced electron-transfer reactions and magnetic field effects on the decay rates of a photogenerated biradical from zinc porphyrin–viologen linked compounds in an ionic liquid

Fluorescence and transient absorption spectra of zinc-porphyrin (ZnP)–viologen linked compounds with various methylene groups indicate that intramolecular electron-transfer from the singlet or triplet excited state of ZnP to viologen occurred and a biradical was generated in the ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) at various temperatures (283–343 K). The decay rate constants of the biradical decreased in 0–0.2∼0.5 T and became constant in 0.2∼0.5–1 T. Unique effects of temperature and methylene chain length on electron-transfer and magnetic field effects were observed and are probably due to the properties of the ionic liquid as compared with benzonitrile.