An Electron Spin Resonance Study of the Phosphorescent States of Some 4- and 4,4′-Substituted Biphenyls

Substituent effects on the unpaired spin distribution of the phosphorescent state for a series of 4- and 4,4′-substituted biphenyls were studied by epr and phosphorescence spectroscopy. No net differences in either epr or phosphorescence results are seen among the various alkyl substituents. Examination of zero-field splitting parameters suggests partial transfer of ir-electron spin density from aromatic rings to silyl and germyl groups. Line-width variation among CH3, CD3, and CF3 derivatives is explained by hyperfine interaction with substituent nuclei. The triplet state epr and phosphorescence results are supported by previously reported polarographic and uv data and by MO theory.