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 ar e 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 t he triplet and ground states form excited complexes. The rates of complex f ormation were measured, which proved to be smaller than the diffusion const ant. This is explained by the successive formation of two types of complexe s in solutions. The mechanisms of complex formation are proposed, which des cribe the corresponding spectral transformations. (C) 2000 MAIK "Nauka/Inte rperiodica".