Analysis of Hydrogen-Bonding Effects on Excited-State Proton-Coupled Electron Transfer from a Series of Phenols to a Re(I) Polypyridyl Complex

Prateek Dongare, Annabell G. Bonn, Somnath Maji, Leif Hammarström

Research output: Contribution to journalArticle

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Abstract

In the present study of proton-coupled electron transfer (PCET) reactions, the excited-state of a fac-[(CO)3ReI(bpy)(4,4′-bpy)]+ (bpy = 2,2′-bipyridine and 4,4′-bpy = 4,4′-bipyridine) complex was reductively quenched by a series of phenols. A variation of substituents on the phenols substantially alters their pKa and E° values and provides an opportunity to study photoinduced PCET as a function of their redox properties. Analyses of absorption spectral changes indicate that the phenols form a weak hydrogen bond with the pyridinic nitrogen of the 4,4′-bpy ligand in the ground-state, and ground-state association constant (KA) values were determined. This H-bonded adduct quenches the excited Re complex by PCET from the phenol, to form the reduced and protonated Re complex. The KA values obtained aid quantitative evaluation of the rate constant for the PCET reaction in the H-bonded adduct. Thus, photophysical studies and mechanistic analysis indicate that the reaction occurs via a concerted mechanistic pathway, for the unsubstituted phenol and phenols with electron-withdrawing substituents. Furthermore, the magnitude of the quenching varies systematically with the proton-coupled potentials of the phenols and not their hydrogen-bonding strength (as reflected in KA). This study is one of the first detailed analyses of intermolecular H-bonding between a self-assembling metal complex and a series of substituted phenols in an effort to study their relationship with the kinetic parameters in a photoinduced CPET reaction.

Original languageEnglish
Pages (from-to)12569-12576
Number of pages8
JournalJournal of Physical Chemistry C
Volume121
Issue number23
DOIs
Publication statusPublished - Jun 15 2017

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Phenols
Excited states
phenols
Protons
Hydrogen bonds
electron transfer
protons
Electrons
hydrogen
excitation
Phenol
Ground state
adducts
Coordination Complexes
Carbon Monoxide
Kinetic parameters
ground state
Quenching
Rate constants
Nitrogen

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Surfaces, Coatings and Films
  • Physical and Theoretical Chemistry

Cite this

Analysis of Hydrogen-Bonding Effects on Excited-State Proton-Coupled Electron Transfer from a Series of Phenols to a Re(I) Polypyridyl Complex. / Dongare, Prateek; Bonn, Annabell G.; Maji, Somnath; Hammarström, Leif.

In: Journal of Physical Chemistry C, Vol. 121, No. 23, 15.06.2017, p. 12569-12576.

Research output: Contribution to journalArticle

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