Electron Spin Resonance of 2,2′-Bipyridyl, Dimethyl-2,2′-Bipyridyls, and 2,2′-Biquinolyl in their Phosphorescent Triplet States

Abstract

Abstract Electron spin resonance (ESR) of phosphorescent triplet states of 2,2′-bipyridyl, 3,3′-, 4,4′-, 5,5′-, and 6,6′-dimethyl-2,2′-bipyridyls, and 2,2′-biquinolyl has been studied in ethanol glasses. For 2,2′-bipyridyl, the ESR spectrum of both the E and Z conformers was observed in poly(vinyl alcohol) films and their assignment was examined by changing the direction of applied magnetic field. Using such a technique, the stretched polymer-film method has been developed for determining the molecular conformations which are difficult to be estimated from zero-field splitting (ZFS) parameters obtained in rigid glasses. As a result, the conformations in the phosphorescent triplet states of molecules studied here are confirmed to be all E in ethanol glasses, even for a case with a relatively small E value.