Influence of quenchers on excited complexes upon triplet-triplet annihilation of tetrapyrrole molecules in liquid solutions

The influence of triplet quenchers on the kinetics of triplet-triplet annih ilation (TTA) for chlorophyll a and tetraphenylporphine was investigated. I t was found that the rate constants for the quenching of triplet states by TTA increase with increasing the quencher concentration [Q]. The greatest v alues for the triplet deactivation parameter are proportional to [Q](2) Exp erimental results are consistent with the rationalization of the triplet an nihilation through the formation of complexes from the triplet molecules. T he linear dependence of the degradation rate constant of the triplet-triple t complexes to the ground-state molecules on [Q](2) suggests that two quenc her molecules are necessary for the quenching of one complex molecule. This means that two locally excited triplet states exist in the complex. It is likely the spin correlation time of the triplet states is longer than the l ifetime of the complexes.