Sp. Chen et al., A SPECTROELECTROCHEMICAL INVESTIGATION OF THE REDUCTION OF THE WATER-SOLUBLE MNTSPP - SERS SPECTRA OF MN(II)TSPP, JOURNAL OF PHYSICAL CHEMISTRY B, 102(45), 1998, pp. 9101-9108
Electrochemical and surface spectroscopic techniques are used to inves
tigate the reductive electrochemistry of the water-soluble manganese t
etrasulfonatophenyl porphyrin. The electrocehmistry of MnTSPP at a Ag,
Au, and Pt electrode and the normal Raman and surface-enhanced Raman
scattering spectra of the two redox forms of MnTSPP were studied. Volt
ammetric studies indicate two reductive peaks at -0.45 and -0.85 V on
an Ag electrode. Potential-dependent shifts in the 466 nm UV/vis absor
bance band to 432 nm at -0.5 V on a gold minigrid electrode indicate t
hat reduction of the porphyrin central metal from Mn-III to Mn-II occu
rs at this potential. A 32 cm(-1) downshift in the nu(4) vibration fro
m 1368 to 1336 cm(-1) at -0.5 V is further evidence for the reduction
of the metal from the Mn-III to the Mn-II state. The reduction of the
porphyrin macrocyclic ring to the radical anion is also observed at -0
.8 V. The core-sensitive modes of aquo Mn-III TSPP are in excellent ag
reement with that of a 6-coordinate species. Upon reduction to the (Mn
TSPP)-T-II, the core size marker frequencies shift to those of a 5-coo
rdinate species. Finally, Raman band frequencies for the solution and
SERS spectra are systematically assigned, and normal Raman and surface
-enhanced Raman spectra are presented for (MnTSPP)-T-III and its reduc
ed (MnTSPP)-T-II.