Resonance Raman spectra of the nickel, cobalt, and copper chelates of mesoporphyrin IX dimethyl ester

Resonance Raman spectra have been obtained for the Ni, Co, and Cu chelates of mesoporphyrin IX dimethyl ester in solution using the tunable Rhodamine 6G dye and Ar⁺ lasers. Several bands show variation of intensity and depolarization ratio with exciting wavelength. Excitation profiles for some isolated bands peak at the maxima of the corresponding a electronic absorption bands. The variation of depolarization ratio for some anomalously polarized bands (ρ_l>3/4) has been interpreted in terms of lowering of the symmetry of metalloporphyrins from D_4h. The rigorous symmetry of these chelates is proposed as C_s because of the effect of peripheral substituents. A vibrational assignment is suggested for some of the metal sensitive modes.