Photochemistry of 5-Hydroxy-4'-Dimethylaminoflavylium in the presence of SDS micelles. The role of metastable states of flavylium cation-quinoidal base and trans-chalcones

Paula Araújo, Johan Mendoza, Fernando Pina, Ana Rita Pereira, Iva Fernandes, Victor de Freitas, Joana Oliveira

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Abstract

The multistate of species originated by the compound 5-hydroxy-4′-dimethylaminoflavylium was studied in the presence of sodium dodecyl sulfate micelles 0.1 M. A series of pH jumps obtained by addition of base to the equilibrated solutions of the flavylium cation results in a metastable equilibrium between the flavylium cation and the quinoidal base with pKa = 7.6. In neutral to moderately basic medium, only at 60 °C and after 5 days a new distribution involving the flavylium cation and trans-chalcones is achieved. On the other hand, the anionic trans-chalcone can be formed in few minutes in very basic medium at room temperature and from this, another meta-stable state constituted by protonated, neutral and anionic trans-chalcones, pKCt+/Ct = 2.6 and pKCt/Ct- = 10.7 is reached. The equilibrium is apparently attained between flavylium cation, neutral and anionic trans-chalcones respectively for pKAH+/Ct = 4.1 and pKCt/Ct- = 10.7. Irradiation of the neutral (stable or metastable) and protonated (meta-stable) trans-chalcones yields to the appearance of the quinoidal base or the flavylium cation in an extended pH region 1 < pH < 10. The peculiar properties of this flavylium based photochromic system are explained by means of an energy level diagram where cis-chalcone and hemiketal lay above the quinoidal base.

Original languageEnglish
Article number112827
JournalJournal of Photochemistry and Photobiology A: Chemistry
Volume402
DOIs
Publication statusPublished - 1 Nov 2020

Keywords

  • Aminoflavylium
  • Anthocyanins
  • Meta-stability
  • Photochromism
  • Quinoidal base
  • Trans-Chalcones

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