Studies on Phenothiazinyl Radicals

During the course of numerous studies on phenothiazine radicals, it has been indicated by electron spin resonance (ESR) method that neutral phenothiazinyl radical which is rather unstable can be produced from phenothiazine by several methods. However, any work has not been published regarding the electronic absorption spectrum of these radicals. This may be chiefly because, as seen in general, measuring and assigning the spectrum of such unstable radical are seriously prevented from coexistence of various radical decay products. In this note we shall report the electronic absorption spectra of non-substituted and 1-methylsubstituted phenothiazinyl radicals which are generated in degassed dimethylsulfoxide-acetic anhydride mixture. By referring to the ESR spectra in the same systems and by performing theoretical calculations on the electronic transition of the radicals, a brief comment will be given to the assignment of the new absorption maxima in the electronic absorption spectra.