Chlorpromazine (CPZ), fluphenazine (FPZ) and trifluoperazine (TFP) are phenothiazine derivatives, which generate photoproducts under UV irradiation. We observed that CPZ develops three fluorescent fotoproducts under different conditions. Promazine (PZ) that forms from the CPZ photolysis. The chlorine loss is one of the main pathways for photoproduct formation and it seems to be a requirement for development of CPZ dimers or trimers. The sulfoxide species with fluorescence peak at (aprroxomately) 370 nm develops in the presence of oxygen only in acid conditions. Another fluorescent species with structured emission and maximum at 352 nm develops primarily in the absence of oxygen. It was observed that the development rates of all fluorescent photoproduct are greater under acidic conditions. FPZ and TFP presented the same fluorescent photoproduct (emission (approximately) 410 nm), which develops in the presence of O2 with the same characteristics as the sulfoxide derivative. The fluorescence of the TFP photoproduct was tested as a UV sensor and a sensor for detection of small amounts of oxygen. Studying the interactions with Na+, K+-ATPase enriched membranes, phenothiazines were shown to modify the membrane lipid structure since they increased the fluorescence anisotropy of the membrane probe DPH. The results of phenothiazine interaction with tryptophan residues of the enzyme showed fluorescence quenching of (approximately) 50% of the tryptophan residues, without energy transfer. The local structure of the Na(+), K(+)-ATPase ATP binding site, labeled with FITC, was not affected by the interaction with the phenothiazines, suggesting that the phenothiazine sites are far from the ATP binding site.