Esquarinas e cianinas em interfaces liquidas: aspectos dinamicos em microemulsoes e meios homogeneos

Abstract

Oil continuous iso-octane/AOT/polar solvent (glycerol and formamide) microemulsions (reversed micelles) were studied with Dynamic Light Scattering technique. A comparison with the corresponding aqueous system showed that while the glycerol microemulsion has similar features, stronger attractive forces between the dispersed droplets could be detected. The formamide reversed micelles showed a more complex behaviour, due to a decrease in the interface rigidity attributed to a different solvation of the surfactant polar headgroups. Two molecules of the squaraine family were used as probes of the reversed micelles interfacial physical properties, through the study of its photo physics (solvatochromism and excited singlet state S_1 deactivation) in these systems. The squaraine photo physics was first studied in homogeneous media, where the contribution of hydrogen bonding and quadrupole/dipole interactions were evaluated. The estimation of the polarity and water concentration and activity at the reversed micelle interfacial zone was attempted. A two-state model for the squaraines solubilization at the reversed micelle interface was proposed. Photoinduced and back isomerization of four carbocyanine were studied in neat solvents, in order to understand the influence of the media in the dynamics of these processes. Charge transfer phenomena on the reaction dynamics were detected in this study. In the reversed micelles, the total friction was probed by the photoinduced isomerization of an indocarbocyanine dye, while the dynamic aspects were accessed with the back isomerization of a oxadicarbocyanine. It was concluded that the reaction dynamics were detected in this study. In the reversed micelles, the total friction was probed by the photoinduced isomerization of an indocarbocyanine dye, while the dynamic aspects were accessed with the back isomerization of a oxadicarbocyanine. It was concluded that the reaction kinetics is strongly dependent on the solvation co-ordinate due to variations of the molecule dipolar moment, which change the topology of the reaction potential surfacesAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga