Formal intramolecular photoredox reactions of anthraquinones mediated by water

Date

2011-05-26

Authors

Hou, Yunyan

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Abstract

The formal intramolecular photoredox reaction initially discovered for the parent 2- (hydroxymethyl)-9,10-anthraquinone (HMAQ) in aqueous solution was extended to a variety of anthraquinone derivatives 2.1-2.9, biphenyl anthraquinones 3.1-3.4 and acenequinones 4.1-4.4. The purpose of the study was to explore the generality of the unique photochemical reaction involving HMAQ, understand the mechanism of the reaction and develop potential applications. All the anthraquinones studied (except for 2.4) undergo the formal intramolecular photoredox reaction with a range of quantum yields (PHI =0.02-0.7). Mechanistic studies based on the parent compound HMAQ were carried out by product studies, isotope effects, solvent deuterium isotope effects, pH effect, triplet quenching studies, and laser flash photolysis. It was found that the formal intramolecular photoredox reaction involves a highly polarized triplet excited state in which the electron density of the benzylic CH20H moiety is transferred to the central anthraquinone ring. This highly polarized triplet excited state is subsequently trapped adiabatically by protonation at the anthraquinone carbonyl oxygen.

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Keywords

photochemistry

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