Chemical reaction network of flavylium ions in heterogeneous media

Dissertação apresentada para a obtenção do Grau de Doutor em Química, especialidade em Química-Física, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaFlavylium compounds (2-phenyl 1-benzopyrylium) constitute a versatile family of molecules that illustrates the concept of multistate system, since different forms exhibiting diverse properties can be obtained by means of external inputs such as pH and light. Dramatic changes in the properties of the flavylium network can be observed in heterogeneous media due to specific interactions of some of the states with different chemical microenvironments. In this thesis, the effects of CTAB micelles (chapters 2 and 3), Pluronic micelles and gels (chapter 4)and encapsulation in molecular clips (chapter 5) and zeolite L (chapter 6) on the chemical reaction network of flavylium ions are reported. Positively charged CTAB micelles, stabilizing trans-chalcone species, Ct, can be used to achieve efficient photochromism of flavylium compounds. 2-styryl 1-benzopyrylium salts, obtained by the introduction of a double bond between the benzopyrylium and the phenyl units, exhibit red shifted absorption maxima compared with flavylium analogues (up to 90 nm). This new family of compounds allows the design of photochromic systems based on CTAB micelles; in particular, switching from yellow to light blue using these derivatives of natural anthocyanins is possible. Flash photolysis experiments provided evidence for a singlet state isomerization process. In Pluronic media, photochromic gels based on the flavylium network can be obtained. In chapter 4, the Ct photochromic mechanism was analyzed, using mainly fluorescence techniques such as steady-state, time-resolved and anisotropy. Evidences for Ct distribution among different sites within the Pluronic aggregate and for selective Ct photochemistry were found. Finally, our approach focused on the encapsulation of flavylium salts. The association between a sulphate molecular clip and the several species from the network of a flavylium salt afforded water soluble host-guest complexes that were thoroughly studied. It was demonstrated that hydrophobic interactions between the molecular clips and the flavylium guest molecules are dominant; the other potential interactions, which certainly determine the structures of these host-guest complexes to a large extent, seem to be of minor importance for their stability. The hydration of the flavylium cation was found to be retarded in the presence of clip and the photochemically induced trans-cis isomerization seems essentially unaffected by the sulphate molecular clip. Spectroscopic studies on flavylium compounds encapsulated into the one-dimensional channels of zeolite L revealed drastic changes on fluorescence behavior and it was shown thatCt can isomerize inside the channels of zeolite L