Photochromism of naphthoflavylium. On the role of 4-OH hemiketal in flavylium network

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Abstract

Flavylium compounds suffer in aqueous solution the nucleophilic addition of water at moderately acidic pH values (hydration reaction). The hydration is possible in two positions, namely at position 2, forming hemiketal B2, and at position 4, forming hemiketal B4. B2 can subsequently evolve to give the cis- and trans-chalcone species. At the present work the network of chemical reactions involving the naphthoflavylium compound in aqueous solution was studied by means pH jumps, stopped flow, continuous irradiation and flash photolysis. The equilibrium and rate constants of the system were calculated through a mathematical model. The species 84 has a kinetic effect similar to the one observed for the quinoidal base (for flavylium dyes bearing acidic groups), i.e. 84 is a kinetic product retarding the rate of equilibration. Flash photolysis experiments in comparison with reverse pH jumps results show that the appearance of the flavylium ion is faster in the photochemical-induced process than in the thermal one, suggesting an additional photochemical pathway (besides photoisomerization) after the excitation of the trans-chalcone. (C) 2011 Elsevier B.V. All rights reserved.
Original languageUnknown
Pages (from-to)4-10
JournalJournal Of Photochemistry And Photobiology A-Chemistry
Volume220
Issue number1
Publication statusPublished - 1 Jan 2011

Keywords

    Cite this

    @article{fbdb3180dd434ad0bdd8ab61f2d79c94,
    title = "Photochromism of naphthoflavylium. On the role of 4-OH hemiketal in flavylium network",
    abstract = "Flavylium compounds suffer in aqueous solution the nucleophilic addition of water at moderately acidic pH values (hydration reaction). The hydration is possible in two positions, namely at position 2, forming hemiketal B2, and at position 4, forming hemiketal B4. B2 can subsequently evolve to give the cis- and trans-chalcone species. At the present work the network of chemical reactions involving the naphthoflavylium compound in aqueous solution was studied by means pH jumps, stopped flow, continuous irradiation and flash photolysis. The equilibrium and rate constants of the system were calculated through a mathematical model. The species 84 has a kinetic effect similar to the one observed for the quinoidal base (for flavylium dyes bearing acidic groups), i.e. 84 is a kinetic product retarding the rate of equilibration. Flash photolysis experiments in comparison with reverse pH jumps results show that the appearance of the flavylium ion is faster in the photochemical-induced process than in the thermal one, suggesting an additional photochemical pathway (besides photoisomerization) after the excitation of the trans-chalcone. (C) 2011 Elsevier B.V. All rights reserved.",
    keywords = "Chalcones, Multistate systems, Photochromism, Naphthoflavylium, Hemiketals",
    author = "Pina, {Fernando Jorge da Silva}",
    year = "2011",
    month = "1",
    day = "1",
    language = "Unknown",
    volume = "220",
    pages = "4--10",
    journal = "Journal Of Photochemistry And Photobiology A-Chemistry",
    issn = "1010-6030",
    publisher = "Elsevier Science B.V., Amsterdam.",
    number = "1",

    }

    TY - JOUR

    T1 - Photochromism of naphthoflavylium. On the role of 4-OH hemiketal in flavylium network

    AU - Pina, Fernando Jorge da Silva

    PY - 2011/1/1

    Y1 - 2011/1/1

    N2 - Flavylium compounds suffer in aqueous solution the nucleophilic addition of water at moderately acidic pH values (hydration reaction). The hydration is possible in two positions, namely at position 2, forming hemiketal B2, and at position 4, forming hemiketal B4. B2 can subsequently evolve to give the cis- and trans-chalcone species. At the present work the network of chemical reactions involving the naphthoflavylium compound in aqueous solution was studied by means pH jumps, stopped flow, continuous irradiation and flash photolysis. The equilibrium and rate constants of the system were calculated through a mathematical model. The species 84 has a kinetic effect similar to the one observed for the quinoidal base (for flavylium dyes bearing acidic groups), i.e. 84 is a kinetic product retarding the rate of equilibration. Flash photolysis experiments in comparison with reverse pH jumps results show that the appearance of the flavylium ion is faster in the photochemical-induced process than in the thermal one, suggesting an additional photochemical pathway (besides photoisomerization) after the excitation of the trans-chalcone. (C) 2011 Elsevier B.V. All rights reserved.

    AB - Flavylium compounds suffer in aqueous solution the nucleophilic addition of water at moderately acidic pH values (hydration reaction). The hydration is possible in two positions, namely at position 2, forming hemiketal B2, and at position 4, forming hemiketal B4. B2 can subsequently evolve to give the cis- and trans-chalcone species. At the present work the network of chemical reactions involving the naphthoflavylium compound in aqueous solution was studied by means pH jumps, stopped flow, continuous irradiation and flash photolysis. The equilibrium and rate constants of the system were calculated through a mathematical model. The species 84 has a kinetic effect similar to the one observed for the quinoidal base (for flavylium dyes bearing acidic groups), i.e. 84 is a kinetic product retarding the rate of equilibration. Flash photolysis experiments in comparison with reverse pH jumps results show that the appearance of the flavylium ion is faster in the photochemical-induced process than in the thermal one, suggesting an additional photochemical pathway (besides photoisomerization) after the excitation of the trans-chalcone. (C) 2011 Elsevier B.V. All rights reserved.

    KW - Chalcones

    KW - Multistate systems

    KW - Photochromism

    KW - Naphthoflavylium

    KW - Hemiketals

    M3 - Article

    VL - 220

    SP - 4

    EP - 10

    JO - Journal Of Photochemistry And Photobiology A-Chemistry

    JF - Journal Of Photochemistry And Photobiology A-Chemistry

    SN - 1010-6030

    IS - 1

    ER -