Kinetics teach that electronic coupling lowers the free-energy change that accompanies electron transfer
- Univ. of North Carolina, Chapel Hill, NC (United States)
- Fudan Univ., Shanghai (People's Republic of China)
- The Univ. of British Columbia, Vancouver, BC (Canada)
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. Here, 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–1without 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.
- Research Organization:
- University of North Carolina, Chapel Hill, NC (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- SC0013461
- OSTI ID:
- 1457096
- Alternate ID(s):
- OSTI ID: 1540281
- Journal Information:
- Proceedings of the National Academy of Sciences of the United States of America, Vol. 115, Issue 28; ISSN 0027-8424
- Publisher:
- National Academy of SciencesCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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