Characterization of the T1 state of porphyrin molecules on the basis of numerical modeling of decrease and increase of fluorescence intensity kinetics

Abstract

For a number of porphyrin molecules, it was shown that their excitation by light pulses of a rectangular step shape and a certain duration led to experimentally observed dynamical decrease and increase of fluorescence kinetics due to changes in the population of the lower (metastable) triplet T₁ state. On the basis of exact analytical expressions for a three-energy-level model, a simple analytical relationships between the rate constants of intramolecular processes and experimentally measured parameters of the fluorescence kinetics were obtained. The three-dimensional isotropic orientation of the molecules in the framework of the chosen model was taken into account by numerical methods and allowed to simulate adequately the experimentally observed fluorescence kinetics. The T₁ state lifetimes of the studied porphyrin molecules in polymer matrices were determined from experimental curves using numerical methods for solving inverse problems. The obtained values correlated with literature data. Features and advantages of this approach were discussed.