Electronic effects of one-electron reduction are investigated for
(OV)TPP (vanadyltetraphenylporphine) by the
use of spectroelectrochemical techniques. Cyclic voltammetry (CV),
absorption, and resonance Raman (RR)
spectroscopy of the anion radical are analyzed with the aid of isotope
labeling and normal-coordinate analysis
(NCA) in order to understand the structural changes. The first
reported Q-band excitation RR spectra of the
(OV)TPP anion radical provide important information regarding the
structural distortion of the porphyrin ring
upon one-electron reduction, through detection of A2g
modes. Direct evidence for static distortion of the
porphyrin
ring is provided by the lowered depolarization ratios of the
A2g modes. Moreover, the upshift of the
ν19 vibrational
mode establishes that some of the
Cα-C
m
bonds are strengthened in
the anion. Consideration of the molecular
orbital pattern shows this observation to be consistent with a
B1g and not a B2g Jahn−Teller distortion.
The
normal-mode calculation supports this inference.
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