Journal
LANGMUIR
Volume 25, Issue 1, Pages 594-601Publisher
AMER CHEMICAL SOC
DOI: 10.1021/la802587d
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Funding
- Portuguese FCT-MCTES [POCI/QUI/57735/2004, SFRH/BPD/18214/2004]
- Fundação para a Ciência e a Tecnologia [POCI/QUI/57735/2004] Funding Source: FCT
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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.
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