NEAR‐INFRARED DETECTION OF SINGLET MOLECULAR OXYGEN PRODUCED BY PHOTOSENSITIZATION WITH PROMAZINE and CHLORPROMAZINE

A sensitive near‐infrared detection system has been used to study the steady‐state emission of 1 O 2 at 1268 nra produced by promazine (PZ) and chlorpromazine (CPZ) during photo‐illumination. Singlet molecular oxygen could be detected in a variety of ordinary and perdeuterated organic solvents, but was not detectable in water or deuterium oxide. The emission was enhanced in the perdeuterated organic solvents and could be eliminated by rigorous degassing or by addition of the singlet oxygen scavenger 2,3‐dimethylfuran. Singlet oxygen could not be detected in any of the solvents during irradiation of the sulfoxides of PZ and CPZ. We conclude that in biological systems 1 O 2 production is not a major pathway to phototoxicity for the sulfoxides, while for the parent phenothiazines the formation of 1 O 2 is much more likely to be important in nonpolar environments such as cell membranes than in the aqueous parts of the cell.