U.V. irradiation of N-alkylphenothiazines （1a—c） in carbon tetrachloride produced 3-（phenothiazin-N’-yl-carbonyl）-N′-alkylphenothiazine （2a—b） and/or 3-（N′-alkylphenothiazin-3′-yl-carbonyl）-N-alkylphenothiazine （3b—c） together with the radical cation carbon tetrachloride salt 1+·CCl4-·（4a—c）, presumably via a photoinduced electron transfer mechanism.
Electron transfer reactions take place readily between 2, 2, 6, 6-tetramethylpiperidine oxoammonium ions (1a, 1b) and phenothiazines (2a—2g), giving corresponding nitroxides (3a, 3b) and phenothiazine radical cations (4a—4g). The rate constants for the electron self-exchange reactions between 1 and 3, as well as between 2 and 4, are determined by EPR and ~1H NMR line-broadening effect in acetonitrile. By application of the Marcus theory, the kinetics of the cross-exchange reactions between 1 and 2 is studied.
