Resonance Raman spectra of copper tetraphenylporphyrin: Effects of strong vibronic coupling on excitation profiles and the absorption spectrum

Abstract

Raman excitation profiles of copper tetraphenylporphyrin have been obtained and interpreted in terms of strong vibronic coupling. The Duschinsky mixing of normal modes in the excited Q electronic state has a dominant effect on the excitation profiles and the absorption spectrum. A general theoretical technique for calculating the vibronic states of molecules is described and applied to metalloporphyrins. The analytical expressions obtained from a new perturbation treatment of the vibronic problem permit a detailed physical understanding of strong coupling influences and interference effects observed in copper tetraphenylporphyrin excitation spectra. A modified interpretation of the Q band absorption is indicated.