Quinone-Quinoneimine Tautomerisation of Phenothiazine- and Phenoselenazine-quinonoid Dyes: Isolation of a Quinoneimine Tautomer

Quinone-quinoneimine tautomerisation of phenothiazine- and phenoselenazine-quinonoid dyes has been investigated by means of their visible spectrum. Phenothiazine quinonoid dyes usually have been isolated in the quinine form but in this instance the dyes were isolated in their quinoneimine form, and the equilibrium was shifted to the quinine form in more polar solvents. The calculated absorption maxima of the tautomers, obtained by means of PPP MO method, have been correlated with the observed values, and the structures were confirmed by their n.m.r and u.v. spectra