Spectral manifestations of nonplanarity effects in Pd complexes of porphyrins

Abstract

It is found on the basis of kinetic spectral studies in nonane, dodecane, and vitreous solutions at 77 K (phosphorescence spectra, polarized phosphorescence, decay kinetics, and phosphorescence excitation spectra) that symmetric and nonsymmetric Pd-porphyrins are characterized by the presence of two noninteracting spectrally different long-and short-wavelength forms in the ground state. The existence of the long-wavelength form is associated with the displacement of the central Pd ion from the macrocycle plane, which leads to the formation of the nonplanar “dome” conformation of the porphyrin ligand. In the case of a nonsymmetrically substituted Pd-tetramethyl-diethylporphyrin molecule, the nonplanar conformation of the π-conjugated macrocycle is characterized by the splitting of the triplet state into two components (T 1 and T 2, Δν=90 cm−1 at 77 K). Both narrow components, which have the same decay, form a dual phosphorescence of the long-wavelength form of this compound, which is caused by efficient thermal exchange between T 1 and T 2 levels in the course of deactivation to the ground state.