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Electrochemical proton-coupled electron transfer of an anthracene-based azo dye.

ABSTRACT: Herein, we report the thermodynamics, kinetics, and mechanism for electrochemical proton-coupled electron transfer involving the anthracene-based azo dye azo-OMe. The peak reduction potential of azo-OMe with organic acids spanning the pK _a range of 2.6-23.51 shows a dependence upon the pK _a of the acid when the acid pK _a falls between 8 and 20 (in acetonitrile). A potential-pK _a diagram is constructed and used to estimate the pK _a of the azo-OMe species. Heterogeneous electron-transfer rate constants are obtained using rotating disk electrode voltammetry in combination with Koutecký-Levich and Tafel analysis. Electrochemical analysis shows that the reactions are diffusion limited and are kinetically controlled by the electron-transfer step. Kinetic isotope studies indicate a concerted proton, electron transfer event occurs in the pK _a-dependent range when using trifluoroacetic acid.

SUBMITTER: Oldacre AN

PROVIDER: S-EPMC9052096 | biostudies-literature | 2020 Apr

REPOSITORIES: biostudies-literature

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Electrochemical proton-coupled electron transfer of an anthracene-based azo dye.

Oldacre Amanda N AN Young Elizabeth R ER

RSC advances 20200414 25

Herein, we report the thermodynamics, kinetics, and mechanism for electrochemical proton-coupled electron transfer involving the anthracene-based azo dye azo-OMe. The peak reduction potential of azo-OMe with organic acids spanning the pK a range of 2.6-23.51 shows a dependence upon the pK a of the acid when the acid pK a falls between 8 and 20 (in acetonitrile). A potential-pK a diagram is constructed and used to estimate th ...[more]

PMID: 35497176

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Project description:Designing molecular platforms for controlling proton and electron movement in artificial photosynthetic systems is crucial to efficient catalysis and solar energy conversion. The transfer of both protons and electrons during a reaction is known as proton-coupled electron transfer (PCET) and is used by nature in myriad ways to provide low overpotential pathways for redox reactions and redox leveling, as well as to generate bioenergetic proton currents. Herein, we describe theoretical and electrochemical studies of a series of bioinspired benzimidazole-phenol (BIP) derivatives and a series of dibenzimidazole-phenol (BI2P) analogs with each series bearing the same set of terminal proton-accepting (TPA) groups. The set of TPAs spans more than 6 pK a units. These compounds have been designed to explore the role of the bridging benzimidazole(s) in a one-electron oxidation process coupled to intramolecular proton translocation across either two (the BIP series) or three (the BI2P series) acid/base sites. These molecular constructs feature an electrochemically active phenol connected to the TPA group through a benzimidazole-based bridge, which together with the phenol and TPA group form a covalent framework supporting a Grotthuss-type hydrogen-bonded network. Infrared spectroelectrochemistry demonstrates that upon oxidation of the phenol, protons translocate across this well-defined hydrogen-bonded network to a TPA group. The experimental data show the benzimidazole bridges are non-innocent participants in the PCET process in that the addition of each benzimidazole unit lowers the redox potential of the phenoxyl radical/phenol couple by 60 mV, regardless of the nature of the TPA group. Using a series of hypothetical thermodynamic steps, density functional theory calculations correctly predicted the dependence of the redox potential of the phenoxyl radical/phenol couple on the nature of the final protonated species and provided insight into the thermodynamic role of dibenzimidazole units in the PCET process. This information is crucial for developing molecular "dry proton wires" with these moieties, which can transfer protons via a Grotthuss-type mechanism over long distances without the intervention of water molecules.

Dataset Information

Electrochemical proton-coupled electron transfer of an anthracene-based azo dye.

Publications

Electrochemical proton-coupled electron transfer of an anthracene-based azo dye.

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