Resonance Raman spectra of Cu-etioporphyrins I, I-m e s o-d4, and IV

Abstract

Resonance Raman spectra obtained using the Ar+ and tunable Rhodamine 6G dye lasers are presented for the position isomers Cu−etioporphyrin I and IV in dilute (10−4 M) solution. The spectra show significant differences in several vibrations enabling the molecules to be distinguished. Several anomalously polarized (ρl ≳ 3/4) vibrations are observed which show dispersion of the depolarization ratios. The dispersion of ρl is interpreted as arising from reduction of chromophore symmetry from its idealized D4h. The solution data for Cu−etioporphyrin I and Cu−etioporphyrin IV are consistent with C4h symmetry and C2v symmetry, respectively, thereby demonstrating the sensitivity of resonant Raman scattering to slight perturbations of the chromophore due to peripheral substituents. Resonance Raman data are also presented for the deuterated analog Cu−etioporphyrin I (meso−d4). Several shifts in the vibrational modes are observed and possible vibrational assignments are discussed.