Depolarization dispersion curves of resonance Raman fundamentals of metalloporphyrins and metallophthalocyanines subject to asymmetric perturbations

Abstract

A model is presented that allows the investigation of depolarization dispersion curves of a 1g,a 2g,b 1g and b 2g resonance Raman fundamentals in the region of the Q state of metalloporphyrins and metallophthalocyanines. This dispersion results from electronic and/or vibronic perturbations of A 2g,B 1g and B 2g symmetry due to asymmetric substituents and/or metal ion-ring interaction acting on the porphyrin (phthalocyanine) ring. The electronic perturbations affect the electronic configuration interaction pattern between the four orbital components of the Q and B states, yielding thereby similar depolarization dispersion curves for all modes of a given symmetry, whereas the vibronic perturbations affect selectively the vibronic coupling matrix of a particular mode. Depolarization dispersion curves resulting from A 2g and B 1g perturbations are treated separately, and many helpful perturbational formulas are given for use in analyzing experimental data. Examples of depolarization dispersion curves and excitation profiles of fundamentals of a 1g, a 2g, b 1g and b 2g symmetry are presented. It is shown that strong depolarization dispersion observed in copper chelate of mesoporphyrin IX dimethyl ester for a 1g and a 2g fundamentals can be explained in terms of an A 2g electronic perturbation and a vibronic a 2g perturbation suffered by the a 1g(1131 cm −1) fundamental. Similarly, the depolarization dispersion curves observed for fundamentals in cytochrome c and Pt-phthalocyanine are explained in terms of an electronic B 1g perturbation, together with selective b 1g vibronic perturbations acting on the 1310 cm −1 a 2g fundamental in cytochrome c and the 482 cm −1 b 2g fundamental in Pt-phthalocyanine. The agreement between the depolarization dispersion curves predicted by our model and experimental data is shown to be satisfactory.