Effect of Imidazole on the Electrochemistry of Zinc Porphyrins: An Electrochemical and Computational Study

Abstract

In this study, the electrochemical behavior of zinc meso-substituted porphyrins in the presence of imidazole is examined by using both cyclic voltammetry (CV) and density functional theory (DFT) methods. The results show that the first half-wave oxidation potentials (1st E) of zinc porphyrins complexed with imidazole all move to the negative side, while the second ones (2nd E) move to the positive side, resulting in larger half-wave oxidation potential splittings of the two oxidation states (ΔE = second E - first E) comparing with the zinc porphyrins. By employing DFT calculations, we have found that both sterically controlled inter π-conjugation between porphyrin rings and meso-substituted phenyl groups and deformation of porphyrin rings do play important roles in contributing to the half-wave oxidation potentials. Imidazole exhibits strong effects on the deformation of porphyrin rings which is dominant in determining the first E while the inter π-conjugation between porphyrin rings and meso-substituted phenyl groups mainly contributes to the second E. Without imidazole, the inter π-conjugation between porphyrin rings and meso-substituted phenyl groups is the only important criterion which effects both first E and second E of zinc porphyrins.

Density functional theory investigation of the coordination of Zn(II)-tetraphenylporphyrin with 1,2,3-triazole ligands

“…When compared to a model Zn(II) porphyrin, this third oxidation is effectively more difficult. In agreement with literature data [22,24], this is a diagnostic signature for a coordinated Zn(II)-porphyrin radical cation. Therefore, the complete oxidation of…”

“…As far as the redox potential of the first oxidation is concerned, the complexation of L1 to ZnTPP leads to a smaller first ionization potential (IP 1 ) value meaning that less energy is required to oxidize the Zn(II)-porphyrin subunit in the complex. This is fully consistent with electrochemical data and DFT calculations reported for related imidazole-Zn(II)porphyrin complexes [22] and supports the assignment for E 1 ox and E 2 ox in the voltammograms obtained for compound 3. However, the second ionization potential (IP 2 ) is not in agreement with the experimental findings which revealed that the second oxidation is more difficult for complexed Zn(II)-porphyrins.…”

“…The geometries of the ZnTPP-L1-3 complexes, ZnTPP and L1-3 were optimized at the B3LYP/6-31G(d) level in both the gas phase and in solvents of different polarities (CH 2 Cl 2 and DMF) using the CPCM model. The B3LYP functional combined with 6-31G* or higher basis set has proven its ability to display and predict the physicochemical properties of porphyrin derivatives and large metalloporphyrin supramolecular ensembles [21][22][23]. Relevant thermodynamic and structural parameters of the optimized ZnTPP-L1-3 complexes are summarized in Table . 2.…”

“…7). Moreover, the dihedral angles between the porphyrin and the meso-phenyl substituents are significantly larger in ZnTPP 2+ -L1 when compared to ZnTPP 2+ thus reducing possible π-conjugation that may play a role in the stabilization of the dicationic Zn(II)-porphyrin moiety [22]. The positive shift observed for the second oxidation of the complexed Zn(II)porphyrin subunit must therefore result from a destabilization of the dication and not from a substantial stabilization of the intermediate radical cation.…”

Cooperative Binding of 1-Phenylimidazole to Cobalt(II) Octaethylporphyrin on Graphite: A Quantitative Imaging and Computational Study at Molecular Resolution

“…Porphyrins can also serve to model reactions on a simpler scale . Of these, OEPs represent a set of simple, compact, and highly studied porphyrins that form stable monolayers on a variety of metal surfaces and highly oriented pyrolytic graphite (HOPG). ,, Metallated OEPs (MOEP) have been shown to bind a variety of ligands in solution, the solid state, , and on surfaces. − ,, Although the binding of imidazole and imidazole derivatives to metalloporphyrins has been previously demonstrated, − few studies have reported the binding of these molecules to MOEPs, − , with only one showing imidazole binding to a surface-supported OEP …”