Síntese, caracterização e investigação das propriedades mesomórficas e fotofísicas de benzalazinas simétricas

Abstract

Azines or 2,3-diazabutadienes encompass several groups and classes of molecules capable of presenting mesophoric properties. These classes of compounds are interesting due to their ease of synthesis, good chemical stability, presence of lateral and/or longitudinal diameters, and ability to maintain rigidity. As a result, azines are used in designing anisotropic molecules with liquid crystalline properties and have been applied to the development of optical devices, LCDs, and even biosensors. In parallel, the discovery of Aggregation Induced Emission (AIE) made this class of molecules gain notoriety and applications in developing smart molecular materials with photophysical properties. In this context, this dissertation discusses the synthesis, characterization, and study of the mesomorphic and photophysical properties of three series of benzalazines derived from vanillin and 2,4-dihydroxybenzaldehyde. The synthetic route for the target compounds involved the O-alkylation of hydroxyl-substituted benzaldehydes, followed by the reaction with hydrazine to obtain the symmetric benzalazines. We characterized the target compounds by IR, 1H and 13C NMR and HRMS spectroscopic techniques. We explored the effect of the methoxyl side group on the smectic properties in one series of compounds. We investigated the influence of several alkyl chains on the generation of smectic or columnar phases in the other series. The possibility of restriction of the intramolecular rotation in an acidic medium by the protonation of the azine group and its effect on the fluorescent properties were investigated. Our results show an interesting protonation-induced fluorescence by benzalazines after contact with acidic media in solutions and thin films. This is a relevant result for compounds without ortho-OH groups, since fluorescence is not common for azines without this group, even in the aggregated state.