Electron spin resonance of phosphorescent fluorine-substituted aromatics

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Abstract
The lowest excited triplet state of diphenyl and of six fluorinated derivatives has been investigated by optical and E.S.R. spectroscopy in ethanol solutions at 77 K. Phosphorescence spectra, lifetimes, zero field energies and hyperfine splittings of Δ m =2 and Δ m =1 stationary peaks are reported. The principal axes of the zero field splitting tensors were determined by magnetophotoselection. The data are interpreted using a model for the effects of fluorine substitution introduced in Part I and the fluorine hyperfine coupling tensor derived in that paper. The results are: (i) a clear indication of the planarity of phosphorescent diphenyl; (ii) a spin density map of the diphenyl triplet state. The further application of the fluorine labelling method to determine simply the electronic structure of phosphorescent hydrocarbons is outlined.