title: Hiding and unveiling trans-chalcone in a constrained derivative of 4',7-dihydroxyflavylium in water: a versatile photochromic system.
abstract: A structurally constrained derivative of 4',7-dihydroxyflavylium was studied in aqueous solution and in CTAB micelles by pH jumps, flash photolysis and continuous irradiation with spectroscopic details assessed as well by theoretical calculations. In water, up to pH = 8, the compound shows only acid base chemistry with deprotonation of the flavylium cation to form a quinoidal base that further deprotonates with pKas of 4.8 and 7.4. In the basic region, unprotonated trans-chalcones are formed. No neutral trans-chalcone (Ct) is formed in water preventing the establishment of the well-known photochromism involving photoisomerization of this species with subsequent formation of the flavylium cation. Addition of 0.02 M CTAB drastically changes the mole fraction distribution of species, leading to the formation of Ct (χCt= 1 at pH = 5) and unveiling a photochromic behavior with a pH-tunable colour contrast in a large pH range (2 < pH < 8). The Ct species can be hidden again (irreversibly) upon addition of α-cyclodextrin that disrupts the CTAB micelles, reverting the system to its initial mole fraction distribution of species. These supramolecular inputs work atop the molecular reaction networks by modifying their species' mole fraction distribution.
authors: LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciência e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal. fp@fct.unl.pt ajp@fct.unl.pt.
authors: Márcia
authors: M
authors: Pessêgo
authors: LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciência e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal. fp@fct.unl.pt ajp@fct.unl.pt.
authors: Sandra
authors: S
authors: Gago
authors: LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciência e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal. fp@fct.unl.pt ajp@fct.unl.pt.
authors: Nuno
authors: N
authors: Basílio
authors: LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciência e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal. fp@fct.unl.pt ajp@fct.unl.pt.
authors: César A T
authors: CA
authors: Laia
authors: LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciência e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal. fp@fct.unl.pt ajp@fct.unl.pt.
authors: A
authors: A
authors: Jorge Parola
authors: LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciência e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal. fp@fct.unl.pt ajp@fct.unl.pt.
authors: João C
authors: JC
authors: Lima
authors: LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciência e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal. fp@fct.unl.pt ajp@fct.unl.pt.
authors: Fernando
authors: F
authors: Pina