Influence of the electron-donating properties on the psychotropic activity of phenothiazine derivatives

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Abstract
The electron-donating properties of substituted phenothiazine derivatives and related cyclic compounds have been determined by measuring the maximum of the lowest-energy absorption band of the corresponding charge transfer complexes with tetracyanoethylene and other electron acceptors. Phenothiazine displays a high electron-donating power. The presence and the nature of the side-chain in the 10-position do not significantly influence this property, which is much modified according to the substituent on the 2-position of the ring. The electron donor ability of phenothiazine progressively falls as the Hammet s̀ para constant of this substituent rises. The decrease parallels increase of psychotropic activity. The observations are consistent with the view that an essential part in the mechanism of psychotropic activity of the phenothiazine drugs is played by a positive radical ion.