Raman spectroscopy of polymers of metal protoporphyrin free acids on metal electrodes

TLDR: In this article, the Raman spectra of the nickel protoporphyrin polymer films show that vinyl groups are saturated in the polymer as evidenced by the disappearance or shifts in vinyl-dependent vibrations.

Abstract: Free acid Cu, Ni, and Zn, but not Fe(III) and Sn(OH)/sub 2/, protoporphyrins IX have been oxidatively polymerized via the ring vinyl substituents onto electrode surfaces. Electropolymerization follows a ring oxidation mechanism as previously observed for the protoporphyrin dimethyl esters. Raman spectra of the nickel protoporphyrin polymer films show that vinyl groups are saturated in the polymer as evidenced by the disappearance or shifts in vinyl-dependent vibrations. Appreciable axial ligation of Ni and Cu in the polymer films is also ruled out by the Raman results. Surface enhancement of the Raman scattering is observed for polymer films on silver electrodes but not on platinum and tin oxide electrodes. Differences between the spectra of the first monolayer at the Ag surface and the bulk polymer are slight, but small frequency shifts are detected by applying the Raman difference spectroscopic technique. 24 references, 3 figures, 2 tables.