Role of Intact Hydrogen-Bond Networks in Multiproton-Coupled Electron Transfer

ODELLA, EMMANUEL; URRUTIA, MARÍA N.; SERENO, LEÓNIDES E.; HAMMES-SCHIFFER, SHARON; GUERRA, WALTER D.; GOINGS, JOSHUA J.; GERVALDO, MIGUEL; MOORE, GARY F.; SECOR, MAXIM; WADSWORTH, BRIAN L.; MOORE, THOMAS A.; MOORE, ANA L.

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY

AMER CHEMICAL SOC

Año: 2020 vol. 142 p. 21842 - 21851

0002-7863

The essential role of a well-defined hydrogen-bond network in achieving chemically reversible multiproton translocations triggered by one-electron electrochemical oxidation/reduction isinvestigated by using pyridylbenzimidazole−phenol models. The two molecular architectures designed for these studies differ with respect to the position of the N atom on the pyridyl ring. In one of the structures, a hydrogen-bond network extends uninterrupted across the moleculefrom the phenol to the pyridyl group. Experimental and theoretical evidence indicates that an overall chemically reversible two-protoncoupled electron-transfer process (E2PT) takes place upon electrochemical oxidation of the phenol. This E2PT process yields the pyridinium cation and is observed regardless of the cyclic voltammogram scan rate. In contrast, when the hydrogen-bond network is disrupted, as seen in the isomer, at high scan rates (∼1000 mV s−1) a chemically reversible process is observed with an E1/2 characteristic of a one-proton-coupled electron-transfer process (E1PT). At slow cyclic voltammetric scan rates (