Formation rate constant and features of the excited complexes upon concentration quenching of the triplet state of Pd-porphyrins in toluene

The concentration dependence of the phosphorescence spectra and lifetime are studied for a number of Pd-porphyrins in toluene in the temperature range from 293 to 193 K and at 77 K. The conclusion is made that porphyrins in the triplet and ground states form excited complexes. The rates of complex formation were measured, which proved to be smaller than the diffusion constant. This is explained by the successive formation of two types of complexes in solutions. The mechanisms of complex formation are proposed, which describe the corresponding spectral transformations. (C) 2000 MAIK "Nauka/Interperiodica".