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Photochromism of Photoenolizable Ketones in Quinoline and 1,8-Naphthyridine Series Studied by Time-Resolved Absorption Spectroscopy

For the two photochromic molecules, 3-benzoyl-2-benzyl-1-methyl-1H-quinolin-4-one (QC1) and 3-benzoyl-1,2-dibenzyl-1H-1,8-naphthyridin-4-one (QC18a) as well as the nonphotochromic 3-benzoyl-1-benzyl-2-methyl-1H-1,8-naphthyridin-4-one (QC18b), the full photochemical mechanism, which is based on the p...

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Published in:The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2007-03, Vol.111 (10), p.1737-1745
Main Authors: Aloïse, Stéphane, Réhault, Julien, Moine, Baptiste, Poizat, Olivier, Buntinx, Guy, Lokshin, Vladimir, Valès, Magalie, Samat, André
Format: Article
Language:English
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Summary:For the two photochromic molecules, 3-benzoyl-2-benzyl-1-methyl-1H-quinolin-4-one (QC1) and 3-benzoyl-1,2-dibenzyl-1H-1,8-naphthyridin-4-one (QC18a) as well as the nonphotochromic 3-benzoyl-1-benzyl-2-methyl-1H-1,8-naphthyridin-4-one (QC18b), the full photochemical mechanism, which is based on the photoenolization process, has been elucidated using stationary and time-resolved spectroscopy techniques. After photoexcitation, the S1(n,π*)−T1(n,π*) ISC process involving the exocyclic carbonyl chromophore is demonstrated to occur. Subsequently, γ-hydrogen transfer proceeds very rapidly to give rise to the triplet photoenol with a probable 1,4-biradical structure. For all three molecules, the biradical is clearly detected and proved quantitatively to be the direct precursor of the colored form (photochromic compounds) or ground state starting material (nonphotochromic compound). Solvent effects for the three molecules studied may suggest the existence of intramolecular hydrogen bonding in both biradical and colored form species. Structural effects on the γ-hydrogen transfer rate and biradical decay are related to the photochromic performances.
ISSN:1089-5639
1520-5215
DOI:10.1021/jp064397q