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

Sergei V. Lymar, Mehmed Z. Ertem, Dmitry Polyansky

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

The bimolecular rate coefficients (kobsq) 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 kobsq 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 acetonitrile, but not in dichloromethane. 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.

Original languageEnglish
Pages (from-to)15917-15928
Number of pages12
JournalDalton Transactions
Volume47
Issue number44
DOIs
Publication statusPublished - Jan 1 2018

Fingerprint

Proton transfer
Phenols
Electron transitions
Protons
Electrons
Quenching
Phenol
Deprotonation
Kinetics
Methylene Chloride
Excited states
Isotopes
Charge transfer
Metals
Ligands
Atoms
Hydrogen

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

@article{791b570b5c6b4e7fa96d60bac874fb42,
title = "Solvent-dependent transition from concerted electron-proton to proton transfer in photoinduced reactions between phenols and polypyridine Ru complexes with proton-accepting sites",
abstract = "The bimolecular rate coefficients (kobsq) 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 kobsq 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 acetonitrile, but not in dichloromethane. 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.",
author = "Lymar, {Sergei V.} and Ertem, {Mehmed Z.} and Dmitry Polyansky",
year = "2018",
month = "1",
day = "1",
doi = "10.1039/C8DT03858A",
language = "English",
volume = "47",
pages = "15917--15928",
journal = "Dalton Transactions",
issn = "1477-9226",
publisher = "Royal Society of Chemistry",
number = "44",

}

TY - JOUR

T1 - Solvent-dependent transition from concerted electron-proton to proton transfer in photoinduced reactions between phenols and polypyridine Ru complexes with proton-accepting sites

AU - Lymar, Sergei V.

AU - Ertem, Mehmed Z.

AU - Polyansky, Dmitry

PY - 2018/1/1

Y1 - 2018/1/1

N2 - The bimolecular rate coefficients (kobsq) 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 kobsq 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 acetonitrile, but not in dichloromethane. 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.

AB - The bimolecular rate coefficients (kobsq) 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 kobsq 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 acetonitrile, but not in dichloromethane. 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.

UR - http://www.scopus.com/inward/record.url?scp=85056345909&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85056345909&partnerID=8YFLogxK

U2 - 10.1039/C8DT03858A

DO - 10.1039/C8DT03858A

M3 - Article

C2 - 30375615

AN - SCOPUS:85056345909

VL - 47

SP - 15917

EP - 15928

JO - Dalton Transactions

JF - Dalton Transactions

SN - 1477-9226

IS - 44

ER -