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Title: Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes

Abstract

The simultaneous, concerted transfer of electrons and protons—electron-proton transfer (EPT)—is an important mechanism utilized in chemistry and biology to avoid high energy intermediates. There are many examples of thermally activated EPT in ground-state reactions and in excited states following photoexcitation and thermal relaxation. Here we report application of ultrafast excitation with absorption and Raman monitoring to detect a photochemically driven EPT process (photo-EPT). In this process, both electrons and protons are transferred during the absorption of a photon. Photo-EPT is induced by intramolecular charge-transfer (ICT) excitation of hydrogen-bonded-base adducts with either a coumarin dye or 4-nitro-4'-biphenylphenol. Femtosecond transient absorption spectral measurements following ICT excitation reveal the appearance of two spectroscopically distinct states having different dynamical signatures. One of these states corresponds to a conventional ICT excited state in which the transferring H⁺ is initially associated with the proton donor. Proton transfer to the base (B) then occurs on the picosecond time scale. The other state is an ICT-EPT photoproduct. Upon excitation it forms initially in the nuclear configuration of the ground state by application of the Franck–Condon principle. However, due to the change in electronic configuration induced by the transition, excitation is accompanied by proton transfer with the protonated basemore » formed with a highly elongated ⁺H–B bond. Coherent Raman spectroscopy confirms the presence of a vibrational mode corresponding to the protonated base in the optically prepared state.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. Univ. North Carolina, Chapel Hill, NC (United States)
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Center for Solar Fuels (UNC EFRC)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1065648
DOE Contract Number:  
SC0001011
Resource Type:
Journal Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 108 (21); Journal Issue: 21; Related Information: UNC partners with University of North Carolina (lead); Duke University; University of Florida; Georgia Institute of Technology; University; North Carolina Central University; Research Triangle Institute; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; catalysis (homogeneous), catalysis (heterogeneous), solar (photovoltaic), solar (fuels), photosynthesis (natural and artificial), hydrogen and fuel cells, electrodes - solar, charge transport, materials and chemistry by design, synthesis (novel materials), synthesis (self-assembly)

Citation Formats

Westlake, Brittany C., Brennaman, Kyle M., Concepcion, Javier J., Paul, Jared J., Bettis, Stephanie E., Hampton, Shaun D., Miller, Stephen A., Lebedeva, Natalia V., Forbes, Malcolm D. E., Moran, Andrew M., Meyer, Thomas J., and Papanikolas, John M. Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes. United States: N. p., 2011. Web. doi:10.1073/pnas.1104811108.
Westlake, Brittany C., Brennaman, Kyle M., Concepcion, Javier J., Paul, Jared J., Bettis, Stephanie E., Hampton, Shaun D., Miller, Stephen A., Lebedeva, Natalia V., Forbes, Malcolm D. E., Moran, Andrew M., Meyer, Thomas J., & Papanikolas, John M. Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes. United States. https://doi.org/10.1073/pnas.1104811108
Westlake, Brittany C., Brennaman, Kyle M., Concepcion, Javier J., Paul, Jared J., Bettis, Stephanie E., Hampton, Shaun D., Miller, Stephen A., Lebedeva, Natalia V., Forbes, Malcolm D. E., Moran, Andrew M., Meyer, Thomas J., and Papanikolas, John M. 2011. "Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes". United States. https://doi.org/10.1073/pnas.1104811108.
@article{osti_1065648,
title = {Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes},
author = {Westlake, Brittany C. and Brennaman, Kyle M. and Concepcion, Javier J. and Paul, Jared J. and Bettis, Stephanie E. and Hampton, Shaun D. and Miller, Stephen A. and Lebedeva, Natalia V. and Forbes, Malcolm D. E. and Moran, Andrew M. and Meyer, Thomas J. and Papanikolas, John M.},
abstractNote = {The simultaneous, concerted transfer of electrons and protons—electron-proton transfer (EPT)—is an important mechanism utilized in chemistry and biology to avoid high energy intermediates. There are many examples of thermally activated EPT in ground-state reactions and in excited states following photoexcitation and thermal relaxation. Here we report application of ultrafast excitation with absorption and Raman monitoring to detect a photochemically driven EPT process (photo-EPT). In this process, both electrons and protons are transferred during the absorption of a photon. Photo-EPT is induced by intramolecular charge-transfer (ICT) excitation of hydrogen-bonded-base adducts with either a coumarin dye or 4-nitro-4'-biphenylphenol. Femtosecond transient absorption spectral measurements following ICT excitation reveal the appearance of two spectroscopically distinct states having different dynamical signatures. One of these states corresponds to a conventional ICT excited state in which the transferring H⁺ is initially associated with the proton donor. Proton transfer to the base (B) then occurs on the picosecond time scale. The other state is an ICT-EPT photoproduct. Upon excitation it forms initially in the nuclear configuration of the ground state by application of the Franck–Condon principle. However, due to the change in electronic configuration induced by the transition, excitation is accompanied by proton transfer with the protonated base formed with a highly elongated ⁺H–B bond. Coherent Raman spectroscopy confirms the presence of a vibrational mode corresponding to the protonated base in the optically prepared state.},
doi = {10.1073/pnas.1104811108},
url = {https://www.osti.gov/biblio/1065648}, journal = {Proceedings of the National Academy of Sciences of the United States of America},
issn = {0027-8424},
number = 21,
volume = 108 (21),
place = {United States},
year = {Tue May 24 00:00:00 EDT 2011},
month = {Tue May 24 00:00:00 EDT 2011}
}