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Proton-coupled charge-transfer reactions and photoacidity of N,N-dimethyl-3-arylpropan-1-ammonium chloride salts

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Abstract

Photoinduced intermolecular proton-transfer processes from N,N-dimethyl-3-arylpropan-1-ammonium chloride salts (ArCl, with aryl as 1-pyrenyl, 9-anthryl, and 2-naphtyl) to a solvent molecule have been investigated by steady-state and dynamic spectroscopic methods. The intermolecular proton-transfers are coupled either to the formation of an exciplex or to a solvent-separated ion pair in what we have termed a ‘proton-coupled charge-transfer reaction’. A range of solvents has been observed to mediate both the ground-state conformations of the ArCl and the extent of electron transfer. Unlike typical photoacids, in which through-bond interactions control photoacidity, through-space charge-transfer interactions are responsible in the excited singlet states of the ArCl. Transient absorption experiments reveal a range of electronic comportments in the excited-states of the ArCl. Excited-state pKa values of −3.4, 1.3, and −3.3 in THF were calculated using a Förster-like approach for the 1-pyrenyl, 9-anthryl, and 2-naphthyl salts, respectively. The observed rate of proton-transfer was found to be independent of the thermodynamic driving force and the short-term reversibility of these reactions has been approximated. The data suggest how other systems may be designed to facilitate this novel process.

Graphical abstract: Proton-coupled charge-transfer reactions and photoacidity of N,N-dimethyl-3-arylpropan-1-ammonium chloride salts

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Publication details

The article was received on 06 Feb 2017, accepted on 27 Apr 2017 and first published on 09 May 2017


Article type: Paper
DOI: 10.1039/C7PP00044H
Citation: Photochem. Photobiol. Sci., 2017, Advance Article
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    Proton-coupled charge-transfer reactions and photoacidity of N,N-dimethyl-3-arylpropan-1-ammonium chloride salts

    T. M. Safko, S. Jiang, L. Zhang, Q. Zhang and R. G. Weiss, Photochem. Photobiol. Sci., 2017, Advance Article , DOI: 10.1039/C7PP00044H

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