Resonance Raman spectra of Cuhyphen;etioporphyrins I, Ihyphen;mesohyphen;d4, and IV

摘要

Resonance Raman spectra obtained using the Ar+and tunable Rhodamine 6G dye lasers are presented for the position isomers Cuminus;etioporphyrin I and IV in dilute (10minus;4M) solution. The spectra show significant differences in several vibrations enabling the molecules to be distinguished. Several anomalously polarized (rgr;lgsim; 3/4) vibrations are observed which show dispersion of the depolarization ratios. The dispersion of rgr;lis interpreted as arising from reduction of chromophore symmetry from its idealizedD4h. The solution data for Cuminus;etioporphyrin I and Cuminus;etioporphyrin IV are consistent withC4hsymmetry andC2vsymmetry, 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 Cuminus;etioporphyrin I (mesominus;d4). Several shifts in the vibrational modes are observed and possible vibrational assignments are discussed.