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Title: Solvent-dependent transition from concerted electron–proton to proton transfer in photoinduced reactions between phenols and polypyridine Ru complexes with proton-accepting sites

The bimolecular rate coefficients ($$k_q^{obs}$$) for quenching the metal-to-ligand charge transfer excited states of two Ru polypyridine complexes containing H-bond accepting sites by six p-substituted phenols exhibit abrupt deviations from the expected linear correlations of log$$k_q^{obs}$$ with phenol’s Hammett σ p constant. This pattern is attributed to a transition of the quenching mechanism from a concerted electron-proton transfer (EPT) to a proton transfer (PT); the latter becomes predominant for the most acidic phenols in MeCN, but not in CH 2Cl 2. This assertion is supported by a detailed thermochemical analysis, which also excludes the quenching pathways involving electron transfer from phenols with or without deprotonation of phenols to the solvent, either concerted or sequential. The transition from EPT to PT upon the σ p increase is consistent/supported by the magnitudes of the measured and computed PhOH/OD kinetic isotope effects and by the observed reduction of the EPT product yields upon replacing the low σ p methoxyphenol by the high σ p nitrophenol. In addition to modulating the relative contribution of the EPT and PT quenching pathways, the solvent strongly affects the bimolecular rate coefficients for the EPT quenching proper. Unlike with H-atom transfer reactions, this kinetic solvent effect could not be quantitatively accounted for by the phenol-solvent H-bonding alone, which suggests a solvent effect on the H-bonding constants in the phenol-Ru complex precursor exciplexes and/or on the unimolecular EPT rate coefficients within these exciplexes.
Authors:
ORCiD logo [1] ;  [1] ; ORCiD logo [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Report Number(s):
BNL-209492-2018-JAAM
Journal ID: ISSN 1477-9226; ICHBD9
Grant/Contract Number:
SC0012704
Type:
Accepted Manuscript
Journal Name:
Dalton Transactions
Additional Journal Information:
Journal Volume: 47; Journal Issue: 44; Journal ID: ISSN 1477-9226
Publisher:
Royal Society of Chemistry
Research Org:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1483559
Alternate Identifier(s):
OSTI ID: 1479827

Lymar, Sergei V., Ertem, Mehmed Z., and Polyansky, Dmitry E.. Solvent-dependent transition from concerted electron–proton to proton transfer in photoinduced reactions between phenols and polypyridine Ru complexes with proton-accepting sites. United States: N. p., Web. doi:10.1039/C8DT03858A.
Lymar, Sergei V., Ertem, Mehmed Z., & Polyansky, Dmitry E.. Solvent-dependent transition from concerted electron–proton to proton transfer in photoinduced reactions between phenols and polypyridine Ru complexes with proton-accepting sites. United States. doi:10.1039/C8DT03858A.
Lymar, Sergei V., Ertem, Mehmed Z., and Polyansky, Dmitry E.. 2018. "Solvent-dependent transition from concerted electron–proton to proton transfer in photoinduced reactions between phenols and polypyridine Ru complexes with proton-accepting sites". United States. doi:10.1039/C8DT03858A.
@article{osti_1483559,
title = {Solvent-dependent transition from concerted electron–proton to proton transfer in photoinduced reactions between phenols and polypyridine Ru complexes with proton-accepting sites},
author = {Lymar, Sergei V. and Ertem, Mehmed Z. and Polyansky, Dmitry E.},
abstractNote = {The bimolecular rate coefficients ($k_q^{obs}$) for quenching the metal-to-ligand charge transfer excited states of two Ru polypyridine complexes containing H-bond accepting sites by six p-substituted phenols exhibit abrupt deviations from the expected linear correlations of log$k_q^{obs}$ with phenol’s Hammett σp constant. This pattern is attributed to a transition of the quenching mechanism from a concerted electron-proton transfer (EPT) to a proton transfer (PT); the latter becomes predominant for the most acidic phenols in MeCN, but not in CH2Cl2. This assertion is supported by a detailed thermochemical analysis, which also excludes the quenching pathways involving electron transfer from phenols with or without deprotonation of phenols to the solvent, either concerted or sequential. The transition from EPT to PT upon the σp increase is consistent/supported by the magnitudes of the measured and computed PhOH/OD kinetic isotope effects and by the observed reduction of the EPT product yields upon replacing the low σp methoxyphenol by the high σp nitrophenol. In addition to modulating the relative contribution of the EPT and PT quenching pathways, the solvent strongly affects the bimolecular rate coefficients for the EPT quenching proper. Unlike with H-atom transfer reactions, this kinetic solvent effect could not be quantitatively accounted for by the phenol-solvent H-bonding alone, which suggests a solvent effect on the H-bonding constants in the phenol-Ru complex precursor exciplexes and/or on the unimolecular EPT rate coefficients within these exciplexes.},
doi = {10.1039/C8DT03858A},
journal = {Dalton Transactions},
number = 44,
volume = 47,
place = {United States},
year = {2018},
month = {10}
}

Works referenced in this record:

Universal Solvation Model Based on Solute Electron Density and on a Continuum Model of the Solvent Defined by the Bulk Dielectric Constant and Atomic Surface Tensions
journal, May 2009
  • Marenich, Aleksandr V.; Cramer, Christopher J.; Truhlar, Donald G.
  • The Journal of Physical Chemistry B, Vol. 113, Issue 18, p. 6378-6396
  • DOI: 10.1021/jp810292n

Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy
journal, January 2005
  • Weigend, Florian; Ahlrichs, Reinhart
  • Physical Chemistry Chemical Physics, Vol. 7, Issue 18, p. 3297-3305
  • DOI: 10.1039/b508541a