Ethynylphenyl-Derivatized Free Base Porphyrins: Anodic Oxidation Processes and Covalent Grafting onto Glassy Carbon Electrodes

Abstract

In six of seven cases, direct anodic oxidation of the ethynyl group of an ethynylphenylderivatized free-base porphyrin gave modified glassy carbon electrodes in which the porphyrin was strongly surface-bound, most likely in a perpendicular geometry through covalent attachment of the ethynyl group to a surface carbon atom. The porphyrins each contained an ethynylphenyl group in one meso position and varied in the groups present in the other three meso positions. Electrografted 5,10,15,20-tetrakis(ethynylphenyl)porphyrin, H21, which has ethynyl moieties in all four meso positions, has well-defined surface voltammetry and grows to multi-layer levels upon repeated cyclic voltammetry (CV) deposition scans. Multi-layering was not observed to the same degree for mono-ethynylphenyl-substituted porphyrins, and became progressively less for porphyrins having groups in the 15-meso position that were more protective against ethynyl radical attack. Clean molecular monolayer-level coverage was observed for 5-ethynylphenyl-10,20-bis(3-methoxyphenyl)-15-hexylporphyrin, H25. Owing to the fact that the ethynyl oxidation potential (1.1 to 1.5 V vs ferrocene) is more positive than that of the second macrocycle oxidation, the longevities and follow-up reactions of the porphyrin dications were also studied by CV, chemical oxidation, and optical spectroscopy in homogeneous solution. The primary follow-up products of the doubly oxidized porphyrins, whether surface-bound or in solution, were pyrrole-protonated species that were easily reduced back to the neutral porphyrin.

Functionalization of Carbon Surfaces Using the Copper-Catalyzed Diels–Alder Reaction

“…Considering a temperature of 298 K, a ferrocene surface coverage of Γ = (4.79 ± 0.17) × 10 –11 mol·cm –2 is estimated. Considering the theoretical maximum surface coverage of ferrocenyl moieties of Γ = 4.5 × 10 –10 mol·cm –2 , a 10 times lower surface coverage is achieved under these conditions.…”

“…The lithium-stabilized carbanion formed can be oxidized in a one-electron process to the corresponding ethynyl radical, which then reacts with the surface. The spontaneous interaction of lithium-activated alkynes with the surface, as well as the direct anodic oxidation of terminal alkynes at higher potential, are other possibilities offered by this approach. − …”

A facile approach to create sensitive and selective Cu(ii) sensors on carbon fiber microelectrodes

“…1, but generally appeared in the potential range of 1.5–1.7 V. This is comparable to observations previously reported by Geiger and colleagues for glassy carbon electrodes. 46,47,50…”

Modeling and Experimental Study of the Electron Transfer Kinetics for Non-ideal Electrodes Using Variable-Frequency Square Wave Voltammetry

“…It has been reported that the kinetics of electron transfer reactions could also be extracted from the SWV data using numerical simulations. ,, The computation of the reaction rates using Fourier analysis has been proposed as well. , However, only a small number of reports mention the use of SWV in the development of heterogeneous electrocatalysts, and even then, the method is employed as a qualitative rather than quantitative technique . There are several reasons for such a large gap between the material science and pure analytical chemistry.…”

“…24,25 However, only a small number of reports mention the use of SWV in the development of heterogeneous electrocatalysts, and even then, the method is employed as a qualitative rather than quantitative technique. 26 There are several reasons for such a large gap between the material science and pure analytical chemistry. The first issue arises from the very interpretation of SWV responses for the surface redox transformations as a singlefrequency graph.…”