Photochemical E→Z isomerization of quaternary salt of E-1,2-bispyrazinylethylene

Abstract

With increasing the solvent polarity, the fluorescence maximum for quaternary iodide salt of E-1,2-bispyrazinylethylene(E-BPE) is considerably redshifted and fluorescence quantum yield greatly decreases. However, the difference of fluorescence maximum and quantum yield with increasing the solvent polarity reduces on going from iodice salt to chloride salt. These results indicate that quaternary salt of E-BPE undergoes more efficient electron transfer in the excited singlet state with increasing the solvent polarity and electron donating ability of anion. E-Z photosiomerization for quaternary salt of E-BPE is proved to proceed through the excited triplet state from the azulene quenching study adn its quantum yield is reduced in iodide salt relative to that in chloride salt suggesting that the electron transfer in the excited singlet state should compete efficiently with intersystem crossing to the excited triplet state when anion of salt is efficient electron donor, while for anion with weak electron donating ability the intersystem crossing plays an important role in the excited singlet state and thereby photoisomerization becomes efficient.