Structural Distortion of the Vanadyltetraphenylporphine Anion Radical Probed by Resonance Raman Spectroelectrochemistry

Abstract

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.

The Chemistry and Biochemistry of Vanadium and the Biological Activities Exerted by Vanadium Compounds

“…Upon oxidation, an electron is removed from the porphyrin ring rather than from the metal center. 706,707 Reduction with one electron places the electron in a porphyrin orbital rather than in the metal d orbital 711 analogous to the redox processes observed in oxoiron(IV) porphyrinates. 712 The heme environment in V-containing myoglobin and horseradish peroxidases was synthesized and investigated using EPR spectroscopy.…”

DFT Study on Structural Distortion and Vibronic Coupling of Vanadyl Porphyrin Anion and Cation

“…It is noteworthy that the compositions of SOMO-1, SOMO-2, and LUMO of VOP are quite similar to the HOMO, HOMO-1, and LUMO of ZnP (a typical fourcoordinate planar metalloporphyrin). Therefore, it is not surprising that the VOPs have similar electronic absorption spectra as normal four-coordinate metalloporphyrins [33,34].…”

“…Thus the one-electron reduced (or oxidized) product of VOP can be considered as a π-radical anion (or a π-radical cation). [34]. Geometry optimization have been conducted for the singlet and triplet states of [VOP] − anion.…”

Synthesis and properties of 5,10,15,20-tetra[4-(3,5-dioctoxybenzamidephenyl] porphyrin and its metal complexes

“…27 5,10,15,porphyrin (TAPPH 2 ) was prepared using SnCl 2 /HCl according to the method of Kruper. 5,10,15,20-Tetra-(4-nitrophenyl)porphyrin was synthesized through the reaction between pyrrole and p-nitrobenzaldehyde in the presence of lactic acid according to a published procedure.…”

“…The highly conjugated π-electron skeleton of a porphyrin provides an adequate number of π electrons and π-π* transitions normally give a strong absorption in the UV and visible regions of the spectrum. [9][10][11] To date, the synthesis and application of the substituent tetraphenylporphyrin (TPP) bearing special functional groups have caused great interest, but those bearing an amide group as side chains have been little reported. In order to evaluate the applications of metalloporphyrins, it is necessary to understand the electronic structure and photophysical properties.…”