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

Dongare, P and Bonn, A G and Maji, Somnath and Hammarström, L (2017) Analysis of Hydrogen-Bonding Effects on Excited-State Proton-Coupled Electron Transfer from a Series of Phenols to a Re(I) Polypyridyl Complex. Journal of Physical Chemistry C, 121 (23). pp. 12569-12576. ISSN 1932-7447

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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.

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IITH Creators:
IITH CreatorsORCiD
Maji, Somnathhttp://orcid.org/0000-0001-6047-1339
Item Type: Article
Uncontrolled Keywords: Electron transitions, Ground state, Hydrogen bonds, Metal complexes, Phenols, Rate constants, Rhenium compounds
Subjects: Chemistry
Divisions: Department of Chemistry
Depositing User: Team Library
Date Deposited: 24 Jul 2017 07:17
Last Modified: 09 Oct 2017 09:28
URI: http://raiith.iith.ac.in/id/eprint/3423
Publisher URL: https://doi.org/10.1021/acs.jpcc.7b02449
OA policy: http://www.sherpa.ac.uk/romeo/issn/1932-7447/
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