E.P.R. and zero field ODMR studies of the lowest excited triplet states of halogen containing anilines and anisole

Abstract

The molecular and electronic structures of the lowest excited triplet states of the halogen containing anilines and anisole were studied by means of E.P.R. and zero field ODMR techniques. Single crystal E.P.R. spectra of 4-fluoroaniline and 4-bromoanisole in 1,4-dibromobenzene host show well resolved hyperfine splittings due to halogen nuclei. It is shown that the fluorine hyperfine splitting and the angular dependence of the E.P.R. signal of 4-fluoroaniline can be explained on the basis of the skewed antiquinoid structure of the triplet state. The angular dependence of the E.P.R. signal and the sublevel decay rates of 4-chloroaniline in 1,4-dichlorobenzene also show that the molecule is distorted into an antiquinoid form. The analysis of the bromine hyperfine and quadrupole splittings of 4-bromoanisole indicates that the spin distribution is likely to be similar to that of 4-fluoroaniline.