Hydrogen bond effects on zero field splitting of some 1,4-diazaaromatics with strongly basic lowest triplet states

In polynuclear 1,4-diazines: quinoxaline, 1,4-diazaphenanthrene and 1,4-diazatriphenylene excited to the lowest ³(π, π*) states two effects have been observed and interpreted: (i) D-parameters of the free bases are lower than those of the parent hydrocarbons which seems to be caused by “proximity effects” of the nearby ³(n, π*) states; (ii) in hydrogen bonding solvents D-parameters decrease, just reverse to expectation. The lowest values of D are observed in monovalent cations. The interpretation assumes a non-planar structure of the hydrogen bonded complex.