title: Effect of Methyl, Hydroxyl, and Chloro Substituents in Position 3 of 3',4',7-Trihydroxyflavylium: Stability, Kinetics, and Thermodynamics.
abstract: The effect of methyl, hydroxyl, and chloride substituents in position 3 of the 3',4',7-trihydroxyflavylium core structure was studied. The stability, relative energy of each of chemical species (thermodynamics), and their rates of interconversion (kinetics) are very dependent on these substituents. By comparing the mole fraction distribution at equilibrium of the three multistate systems with the parent 3',4',7-trihydroxyflavylium, introduction of a methyl substituent in position 3 increases the mole fraction of hemiketal at the expense of the trans-chalcone and increases the hydration rate very significantly; a hydroxyl substituent in position 3 gives rise to a degradation process, as observed in anthocyanidins. In the case of 3-chloro-3',4',7-trihydroxyflavylium, a dramatic increase of the flavylium cation acidity was observed and a photochromic system can be operated upon irradiation of the respective trans-chalcone in 1 m HCl. According to the photochromic response of 3,3',4',7-tetrahydroxyflavylium and 3',4',7-trihydroxyflavylium, some requirements for a good photochromic performance are discussed.
authors.affiliation: Departamento de Química Inorgánica y Orgánica, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071, Jaén, Spain.
authors.forename: Alfonso
authors.identifier: http://orcid.org/0000-0001-8691-4628
authors.initials: A
authors.lastname: Alejo-Armijo
authors.affiliation: Departamento de Química Inorgánica y Orgánica, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071, Jaén, Spain.
authors.forename: Sofía
authors.identifier: http://orcid.org/0000-0003-2319-7873
authors.initials: S
authors.lastname: Salido
authors.affiliation: Departamento de Química Inorgánica y Orgánica, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071, Jaén, Spain.
authors.forename: Joaquín
authors.identifier: http://orcid.org/0000-0002-5532-8535
authors.initials: J
authors.lastname: Altarejos
authors.affiliation: LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516, Caparica, Portugal. ajp@fct.unl.pt.
authors.forename: A Jorge
authors.identifier: http://orcid.org/0000-0002-1333-9076
authors.initials: AJ
authors.lastname: Parola
authors.affiliation: LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516, Caparica, Portugal.
authors.forename: Sandra
authors.identifier: http://orcid.org/0000-0003-0221-8508
authors.initials: S
authors.lastname: Gago
authors.affiliation: LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516, Caparica, Portugal.
authors.forename: Nuno
authors.identifier: http://orcid.org/0000-0002-0121-3695
authors.initials: N
authors.lastname: Basílio
authors.affiliation: LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516, Caparica, Portugal.
authors.forename: Luis
authors.identifier: http://orcid.org/0000-0002-3614-9806
authors.initials: L
authors.lastname: Cabrita
authors.affiliation: LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516, Caparica, Portugal. fp@fct.unl.pt.
authors.forename: Fernando
authors.identifier: http://orcid.org/0000-0001-8529-6848
authors.initials: F
authors.lastname: Pina
keywords: dyes/pigments; kinetics; photochromism; substituent effects; thermodynamics