Raman and infrared spectral study of meso-sulfonatophenyl substituted porphyrins (TPPS n, n=1, 2A, 2O, 3, 4)

Abstract

Raman and IR spectra of the free base p-sulfonatophenyl and phenyl meso-substituted porphyrins [5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS 4); 5,10,15-tris(4-sulfonatophenyl)-20-phenyl-porphyrin (TPPS 3); 5,10-bis(4-sulfonatophenyl)-15,20-diphenylporphyrin (TPPS 2A); 5,15-bis(4-sulfonatophenyl)-10,20-diphenylporphyrin (TPPS 2O); and 5-(4-sulfonatophenyl)-10, 15,20-trisphenylporphyrin (TPPS 1)] and their N-diprotonated derivatives (porphyrin diacids) were studied. The Raman spectra of the deuterated analogues of these porphyrins, in which the central hydrogen atoms were substituted with deuterium, were also measured. The observed vibrational bands were assigned on the basis of the deuteration shifts and compared with the structural analogues of these compounds. In IR spectra of the free-base porphyrins, the p-sulfonation of phenyl groups results in evident alteration for the phenyl modes and the porphyrin skeleton modes that are strongly coupled with phenyl vibrations. While the p-sulfonation of phenyl groups causes only slight changes for the high-frequency Raman bands (>850 cm −1), dramatic shifts and band splitting were observed in the low-frequency region (<500 cm −1) of Raman spectra. The observed differences of low-frequency Raman spectra were attributed to the alteration of the structure of the porphyrin ring, especially the C αC mC α bond-angles, by different meso-sulfonatophenyl substitutions. In addition, different packing style of TPPS n molecules in the aggregates is also responsible for the alteration of the vibrational spectra of the aggregated TPPS n .