New feature of the phosphorescence of copper complexes ofmeso-tetraarylporphyrins

Abstract

Introduction of methyl groups in orthopositions of phenyl rings of a Cu-meso-tetraphenylporphin (Cu-TPhP) molecule is shown to lead to a substantial decrease in the diffusivity of the spectrum of low-temperature (77 K) phosphorescence. It is found that the long-lived (580 μsec) and short-lived (0.7 μsec) components of Cu-TPhP phosphorescence differ in emission and absorption (phosphorescence-excitation) spectra and belong to two forms of molecules. The phosphorescence spectrum of the predominant form with small τp is diffuse, while its absorption spectrum is shifted slightly in a bathochromic manner. The phosphorescence spectrum with large τp is structural and is similar to the spectrum of Cu-meso-tetrakis-(ortho-tolyl)porphin. The difference is attributed to the nonplanarity (saddle distortion) of a Cu-TPhP molecule in the lower triplet state in the case of the form with small τp.