Photochromism of 7,4 '-Dihydroxyflavylium in an AOT Reversed Micelle System

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Abstract

The investigation of a flavylium compound in AOT reverse micelles shows photochromic enhancement in a wide pH range, with features previously unobserved in other colloidal systems. In equilibrium, 7,4'-dihydroxyflavylium transforms into trans-chalcone species atpH above 2, but ion-pair formation of the flavylium species with the negatively charged AOT is observed until pH = 5. After irradiation, trans-chalcone species are transformed with high quantum yields into both flavylium and its quinoidal base (through cis-chalcone and hemiketal species) until pH equal to 9. While trans-chalcone is located at the hydrophobic side of the reverse micelle interface, flavylium species tend to solubilize in the water pool. Flash photolysis experiments probe essentially the trans-chalcone solubilization site, showing that photochromic conversion to flavylium species can be achieved without acid catalysis with a unimolecular rate constant of 0.22 s(-1), while the slow recovery to equilibrium after irradiation probes essentially the water pool with a experimental pH-dependent rate constant. The photochromic mechanism is discussed, promising new insights about the possibility of changing the reversed micelle interfacial properties using photoresponsive addictives like flavylium compounds.
Original languageUnknown
Pages (from-to)594-601
JournalLangmuir
Volume25
Issue number1
Publication statusPublished - 1 Jan 2009

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