The effects of intermolecular and intramolecular triplet quenchers and sensitizers on the photochromism of nitrospiropyran have been examined in order to clarify the role of the triplet state (3 A*) as well as that of the excited singlet state (1 A*). The rates of photocoloration and fatigue were significantly affected: the quenchers retarded both rates, while the sensitizers retarded the former but enhanced the latter rate. It can be concluded ...
