PHOTOPHYSICAL PROPERTIES OF SOME 2-(2'-HYDROXYARYL)BENZOTRIAZOLES - DRAMATIC EFFECT OF AN ORTHO-LOCATED BULKY TERT-BUTYL GROUP

Photophysical experiments carried out on 3'-tert-butyl and 5'-tert-butyl analogues of Tinuvin P provided evidence concerning the origin of the so-called ''open'' forms. They result from the rotation of the hydroxyl group followed by the rotation of the phenyl group, not the other way round. This mechanism is consistent with the negligible amount of ''open'' forms in the 3'-tert-butyl derivative in a base so strong as DMSO. In this series of photoprotectors, a bulky alkyl substituent in ortho position with regard to the hydroxyl group improves considerably their photostability.