In the present study, surface-enhanced resonance Raman scattering (SERRS) spectra of α,β,γ,δ-tetra-(4-trimethyl ammonium phenyl) porphyrin [T(4-TAP)P] were obtained. With increasing pH, the relative intensities of the bands at 890 and 1244 cm−1 decreased. These bands were attributed to γ(C-H) and δ(Cm-phenyl), respectively. The bands at 420 and 576 cm−1, which were assigned to γ(phenyl-ring), were enhanced. The molecular symmetry of T(4-TAP)P is discussed in terms of group theory. The bands at 1554 and 1496 cm−1 could be attributed to the vibrational modes of the porphyrin macrocycle; the bands at 1460, 1362, and 1330 cm−1 were assigned to ν(C-C) + δ(C-H), ν(C-N) + δ(C-H), and ν(C-N), respectively. All these bands change in band intensities, positions and widths, with the potential changing from +0.2 V to −0.2 V. It was concluded that the adsorbed porphyrins underwent partial incorporation with Ag from the electrode, and the adsorbate assumed a flat orientation on the silver electrode as well as the Ag colloid surface.
The influence of abstract group theory on molecular symmetry
