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Kinetics teach that electronic coupling lowers the free-energy change that accompanies electron transfer.

ABSTRACT: Electron-transfer theories predict that an increase in the quantum-mechanical mixing (HDA) of electron donor and acceptor wavefunctions at the instant of electron transfer drives equilibrium constants toward unity. Kinetic and equilibrium studies of four acceptor-bridge-donor (A-B-D) compounds reported herein provide experimental validation of this prediction. The compounds have two redox-active groups that differ only by the orientation of the aromatic bridge: a phenyl-thiophene bridge (p) that supports strong electronic coupling of HDA > 1,000 cm-1; and a xylyl-thiophene bridge (x) that prevents planarization and decreases HDA < 100 cm-1 without a significant change in distance. Pulsed-light excitation allowed kinetic determination of the equilibrium constant, Keq In agreement with theory, Keq(p) were closer to unity compared to Keq(x). A van't Hoff analysis provided clear evidence of an adiabatic electron-transfer pathway for p-series and a nonadiabatic pathway for x-series. Collectively, the data show that the absolute magnitude of the thermodynamic driving force for electron transfers are decreased when adiabatic pathways are operative, a finding that should be taken into account in the design of hybrid materials for solar energy conversion.

SUBMITTER: Sampaio RN

PROVIDER: S-EPMC6048547 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

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Kinetics teach that electronic coupling lowers the free-energy change that accompanies electron transfer.

Sampaio Renato N RN Piechota Eric J EJ Troian-Gautier Ludovic L Maurer Andrew B AB Hu Ke K Schauer Phil A PA Blair Amber D AD Berlinguette Curtis P CP Meyer Gerald J GJ

Proceedings of the National Academy of Sciences of the United States of America 20180625 28

Electron-transfer theories predict that an increase in the quantum-mechanical mixing (H<sub>DA</sub>) of electron donor and acceptor wavefunctions at the instant of electron transfer drives equilibrium constants toward unity. Kinetic and equilibrium studies of four acceptor-bridge-donor (A-B-D) compounds reported herein provide experimental validation of this prediction. The compounds have two redox-active groups that differ only by the orientation of the aromatic bridge: a phenyl-thiophene brid ...[more]

PMID: 29941573

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Kinetics teach that electronic coupling lowers the free-energy change that accompanies electron transfer.

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Kinetics teach that electronic coupling lowers the free-energy change that accompanies electron transfer.

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