Free radical studies by resonance Raman spectroscopy: phenothiazine, 10-methylphenothiazine, and phenoxazine radical cations

Abstract

The free radical cations of phenothiazine, 10-methylphenothiazine, and phenoxazine have been formed by chemical oxidation of their parent compounds. The radicals all possess complex, intense visible absorption bands which allow excitation of their resonance Raman spectra throughout the visible region. The point-group symmetries of the parent compounds in solution have been determined as C_s for both phenothiazine and 10-methylphenothiazine, and C_2v for phenoxazine. A partial assignment of the Raman bands has been made for each radical cation studied. The relative intensities of Raman bands and the parent-to-radical frequency shifts observed have been interpreted in terms of the structural changes which occur on radical formation. An analysis of the phenothiazine radical cation visible absorption band, supplemented by resonance Raman data and excitation profiles, has yielded information on the excited-state geometry.