Temperature dependent steric hindrance effects in triplet state relaxation of meso-phenyl-substituted Pd-octaethylporphyrins

Abstract

The analysis of spectral-kinetic results of transient absorption and phosphorescence experiments has been carried out in a wide temperature range (80-293K) for a series of Pd-octaethylporphyrin derivatives (PdOEP) with increasing number of bulky meso-phenyl substituents. In order to elucidate the influence of steric hindrance interactions, as well as porphyrin macrocycle non-planarity on photophysical characteristics and relaxation pathways of triplet states, the following parameters were compared: i) T-state positions on the energy scale, ii) phosphorescence lifetimes and T1 -Tn transient absorption spectra, iii) phosphorescence quantum efficiencies, iv) activation energies of temperature-dependent phosphorescence rate constants for planar PdOEP and non-planar PdOEP-meso(Ph)n molecules.