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

• Type: Article in International Scientific Journal
• Date: 2020

Authors

Araujo, P (Author) Other; Mendoza, J (Author) Other; Pina, F (Author) Other; Pereira, AR (Author) Other; Iva Fernandes (Author) FCUP; Victor de Freitas (Author) FCUP; Joana Oliveira (Author) FCUP

Journal

Title: Journal of Photochemistry and Photobiology A: Chemistry

Vol. 402

ISSN: 1010-6030

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 3 Citations

Scopus - 3 Citations

Other information

Authenticus ID: P-00S-JZA

DOI: 10.1016/j.jphotochem.2020.112827

Abstract (EN): 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 pK(a) = 7.6. In neutral to moderately basic medium, only at 60 degrees 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, pK(Ct+)(/Ct) = 2.6 and pK(Ct/) = 10.7 is reached. The equilibrium is apparently attained between flavylium cation, neutral and anionic transchalcones respectively for pK(AH+/Ct) = 4.1 and pK(Ct/Ct) =10.7. Irradiation of the neutral (stable or metastable) and pmtonated (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.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 9