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Excited state intramolecular proton transfer (ESIPT) from phenol OH (OD) to adjacent “aromatic” carbons in simple biphenyls

Paper ID Volume ID Publish Year Pages File Format Full-Text
27224 44010 2009 8 PDF Available
Title
Excited state intramolecular proton transfer (ESIPT) from phenol OH (OD) to adjacent “aromatic” carbons in simple biphenyls
Abstract

This work reports results of further studies on a new class of excited state intramolecular proton transfer (ESIPT), from phenol OH to adjacent aromatic carbon atoms of suitably designed biphenyl systems. For this purpose, a number of 2-phenylphenols 3–6 with methyl and methoxy substituents on the adjacent proton accepting phenyl ring were synthesized. In particular, we were also interested in studying the effect of an acetyl (ketone) substituent on the proton accepting ring (biphenyl 7) and the effect on the photochemistry when the ketone is reduced to alcohol (biphenyl 8). All compounds except for 7 were found to undergo deuterium exchange (Фex = 0.019–0.079) primarily at the 2′-position on photolysis in 1:3 D2O–CH3CN. This is consistent with a reaction mechanism involving initial ESIPT from the phenol OH to the 2′-position of the adjacent phenyl ring, to generate a biphenyl quinone methide intermediate which rapidly tautomerizes back to starting material. Biphenyl 8 also undergoes a competing photosolvolysis reaction (overall loss of water). Both photosolvolysis and ESIPT reactions react via isomeric quinone methide intermediates and are best interpreted as arising from an excited singlet state that possesses a large degree of charge transfer character, from the phenol ring to the attached phenyl ring. The failure of 7 to react may be due to two possible reasons: (i) high intersystem crossing rate to a non-polarized triplet excited state and/or (ii) a polarized singlet state that is now much more basic at the carbonyl oxygen. The results are consistent with qualitative examination of calculated HOMOs and LUMOs (AM1).

Keywords
Excited state intramolecular proton transfer (ESIPT); Photosolvolysis; Biphenyl quinone methide
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Excited state intramolecular proton transfer (ESIPT) from phenol OH (OD) to adjacent “aromatic” carbons in simple biphenyls
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 208, Issue 1, 15 November 2009, Pages 42–49
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us