Electron spin resonance of phosphorescent fluorine-substituted aromatics

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Abstract
The E.S.R. spectra of triplet state 4-fluorobiphenyl in a dibenzofuran single crystal is analysed to provide further support for the ‘fluorine labelling method’ outlined in parts I and II of this series. This method is then applied to the study of some o,o'-bridged biphenyls in rigid glasses. It is confirmed that the electronic structure of all these species can be well described by that of the biphenyl triplet state. Small variations in zero-field splittings can be explained better by an inductive effect of the heteroatom on the neighbouring carbon and by a geometrical rotation of the two phenyl rings in the molecular plane rather than by a conjugation through the heteroatom.