Influence of the lifetime of a metastable triplet state of photostable organic fluorophores on the kinetics of fluorescence fading and recovery.

The kinetics of rapid fluorescence fading and recovery (anti-fading) of photostable organic fluorophores under two-stage rectangular modulated photoexcitation was studied using computer modeling in the framework of a three-level energy diagram. The fading and recovery were due to an abrupt change in the population rate of the metastable T state. The calculations revealed the presence of an anti-fading process. The modeling results were confirmed by experimental measurements of the fluorescence of a zinc complex of a substituted tetrabenzoporphyrin in an organic polymer. Precise analytical expressions establishing the relationship between the intramolecular rate constants of the photophysical processes and the measured fluorescence parameters were derived. [ABSTRACT FROM AUTHOR]