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These compounds lead to a network of chemical reactions depending on pH\u2005value, light, and solvent. In water, when the pH\u2005value is lowered, the ionized <jats:italic>trans<\/jats:italic>\u2010chalcone is protonated and the flavylium cation <jats:bold>A<\/jats:bold>H<jats:sup>+<\/jats:sup> is formed at very acidic pH\u2005values through hemiketal <jats:bold>B<\/jats:bold> and <jats:italic>cis<\/jats:italic>\u2010chalcone <jats:bold>Cc<\/jats:bold>, with global acidity constants of p<jats:italic>K<\/jats:italic>\u2032<jats:sub>a<\/jats:sub> \u2264\u22121 and \u22480.1, respectively, for <jats:bold>2<\/jats:bold> and <jats:bold>3<\/jats:bold>. The electron\u2010acceptor character of the carboxylic substituent not only increases the observed acidity of the flavylium cation, but also decreases the rate of the ring\u2010opening\/\u2010closing from a subsecond timescale to hours relative to model compound <jats:bold>1<\/jats:bold> (without carboxylate). The photochemistry of the network was studied in detail by means of continuous irradiation, monitored by UV\/Vis absorption and <jats:sup>1<\/jats:sup>H and <jats:sup>13<\/jats:sup>C\u2005NMR spectroscopic analysis. Although compound <jats:bold>3<\/jats:bold> is only slightly photoactive, compound <jats:bold>2<\/jats:bold> (<jats:bold>Ct<jats:sup>\u2212<\/jats:sup><\/jats:bold>) reacts in aqueous solutions (<jats:italic>\u03bb<\/jats:italic><jats:sub>irr<\/jats:sub>=313\u2005nm) to form <jats:bold>B<jats:sup>\u2212<\/jats:sup><\/jats:bold>and <jats:bold>Cc<jats:sup>\u2212<\/jats:sup><\/jats:bold>, with a global quantum yield of 0.15, and fully reverts back to <jats:bold>Ct<jats:sup>\u2212<\/jats:sup><\/jats:bold> with a rate constant of <jats:italic>k<\/jats:italic>=6.7\u00d710<jats:sup>\u22125<\/jats:sup>\u2009s<jats:sup>\u22121<\/jats:sup>. The flavylium cation is no longer formed in methanol, and irradiation of <jats:bold>Ct<jats:sup>\u2212<\/jats:sup><\/jats:bold> leads to the formation of <jats:bold>B<\/jats:bold><jats:sup>\u2212<\/jats:sup> and the new lactone\u2010trapped chromene species <jats:bold>La<\/jats:bold>. The formation of <jats:bold>La<\/jats:bold> takes place through a sequence of three photochemical steps: photoisomerization of <jats:bold>Ct<\/jats:bold><jats:sup>\u2212<\/jats:sup>, photo\u2010ring\u2010closing reaction of <jats:bold>Cc<\/jats:bold><jats:sup>\u2212<\/jats:sup>, and photolactonization of <jats:bold>B<\/jats:bold><jats:sup>\u2212<\/jats:sup>. Only the <jats:italic>cis<\/jats:italic>\/<jats:italic>trans<\/jats:italic> isomerization and ring\u2010closing reactions are thermally reversible on a timescale of seconds and hours, respectively. A photochromic system was achieved in rigid matrices of methanol (at 77\u2005K) and 1\u2010dodecanol (5\u2009\u00b0C) by irradiating lactone <jats:bold>La<\/jats:bold> to give a red <jats:italic>ortho<\/jats:italic>\u2010quinone allide through a photo\u2010ring\u2010opening reaction; the color disappears with a rate constant of <jats:italic>k<\/jats:italic>=1.25\u00d710<jats:sup>\u22122<\/jats:sup>\u2009s<jats:sup>\u22121<\/jats:sup> in 1\u2010dodecanol at 5\u2009\u00b0C.<\/jats:p>","DOI":"10.1002\/chem.201002781","type":"journal-article","created":{"date-parts":[[2011,2,21]],"date-time":"2011-02-21T09:46:47Z","timestamp":1298281607000},"page":"3663-3671","source":"Crossref","is-referenced-by-count":7,"title":["Phase\u2010Dependent Photochromism of a Lactone\u2010Stabilized Chromene from a Flavylium Reaction Network"],"prefix":"10.1002","volume":"17","author":[{"given":"Yoann","family":"Leydet","sequence":"first","affiliation":[]},{"given":"Raquel","family":"Gavara","sequence":"additional","affiliation":[]},{"given":"Lu\u00eds","family":"Cunha\u2010Silva","sequence":"additional","affiliation":[]},{"given":"A. 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