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 annihilation (TTA) for chlorophylla and tetraphenylporphine was investigated. It was found that the rate constants for the quenching of triplet states by TTA increase with increasing the quencher concentration [Q]. The greatest values for the triplet deactivation parameter are proportional to [Q]. Experimental results are consistent with the rationalization of the triplet annihilation through the formation of complexes from the triplet molecules. The linear dependence of the degradation rate constant of the triplet-triplet complexes to the ground-state molecules on [Q]2 suggests that two quencher 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 lifetime of the complexes.