An electron spin, ENDOR, and TRIPLE resonance and INDO study of fluorine-substituted N,N′-diphenyl-4,4′-bipyridylium radical cations

Abstract

E.s.r., ENDOR, and TRIPLE resonance results are reported for the radical cation of N,N′-diphenyl-4,4′-bipyridylium dichloride and a series of its fiuorophenyl analogues. The effect of ortho-, meta-, and para-substitution on the spin density distribution within the molecule is discussed and the observed coupling constants for the fluorine-substituted phenyl derivatives are analysed with the aid of INDO molecular orbital calculations. The magnitude of the spin delocalised into the phenyl rings when ortho-substituted suggests that these rings are substantially twisted with respect to the plane of the bipyridylium rings.