Quenching of excited complexes by Fe-octaethylporphin in triplet-triplet annihilation of Mg-phthalocyanine in liquid solutions

The effect of triplet-state quenchers on the kinetics of triplet-triplet annihilation (TTA) of Mg-phthalocyanine (Mg-Phc) is studied. It is found that the rate constant of triplet-state quenching caused by TTA increases with increasing concentration Q] of quenchers. The maximum values of the relaxation parameter of triplet states are proportional to Q]². The experimental data correspond to TTA with the formation of TT complexes from molecules in triplet states. The proportionality of the decay rate of TT complexes into molecules in the ground state to Q]² suggests that two quenching molecules are required for quenching one TT complex. It seems that the complex contains two locally excited triplet states of individual molecules. The spin correlation time in the triplet state seems to be longer than the average lifetime of complexes (≤10^?4 s). The quenching probability of triplet states in complexes (caused, in particular, by the energy of charge transfer) is lower than the probability of intermolecular triplet energy transfer to the quencher levels.