Síntese de (E)-4-(estiril) fenóis nitro-substituídos e aplicações como sondas na investigação da polaridade de solventes puros, de misturas binárias de solventes e da micropolaridade de ciclodextrinas

Abstract

Uma série de (E)-4-(estiril)fenóis nitro-substituídos foi estudada como sondas solvatocrômicas. Inicialmente, sete compostos foram sintetizados através da reação de condensação dos 4-hidroxibenzaldeídos com o 4-nitrotolueno ou com o 2,4-dinitrotolueno na presença de base. Estes compostos, na sua forma desprotonada, revelaram ser corantes solvatocrômicos. Assim, foram empregados como sondas de polaridade em 28 diferentes solventes puros, por meio da análise de seus espectros de ultravioleta-visível em solução onde sei observou que os compostos apresentam solvatocromismo reverso. Aplicaram-se aos dados as estratégias multiparamétricas de Catalán e Kamlet-Abboud-Taft, com o intuito de compreender a contribuição dos parâmetros dos solventes, como a acidez, a basicidade e a polaridade/polarizabilidade, sobre o solvatocromismo dos corantes estudados. Utilizaram-se alguns corantes na investigação de polaridade de misturas de água e álcoois, observando que a solvatação preferencial ocorre em todos os casos estudados. Por fim, foram realizados estudos da interação dos corantes com diferentes ciclodextrinas (CDs). Observou-se em alguns casos o deslocamento batocrômico da banda solvatocrômica do corante e a formação de complexos de inclusão entre o corante e a CD, indicando a transferência do corante de um ambiente hidrofílico, polar, para o ambiente menos polar referente à cavidade da CD.<br>

Abstract : A series of nitro-substituted (E)-4-(styryl)phenols was studied as solvatochromic probes in this dissertation. Firstly, seven compounds were synthesized through the condensation of the hydroxybenzaldehydes with 4-nitrotoluene or 2,4-di-nitrotoluene, in the presence of base. All compounds were characterized using IR, 1H NMR, and mass spectrometric techniques, as well as by melting points. These compounds, in their deprotonated form, revealed to be solvatochromic dyes. Thus, they were applied as polarity probes in 28 different pure solvents, by means of the analysis of their ultraviolet-visible spectra in solution. The maxima in the absorption wavelengths were obtained from the spectra in each solvent and used to determine the respective transition energy values. It was observed that the compounds exhibited reverse solvatochromism: the more polar solvents are capable to stabilize better the benzenoid form of the dye, which gives the more important contribution to stabilize the ground state, being responsible for the observed negative solvatochromism. In the less polar solvents, however, the quinonoid form contributes better to the ground state, causing a reversal in the solvatochromism. The Catalán and Kamlet-Abboud-Taft multiparametric approaches were applied to the experimental data aiming to understand the contribution of the solvent parameters, such as acidity, basicity, and polarity/polarizability, on the solvatochromism of the studied dyes. Some dyes of the series were used to investigate the polarity of water-alcohol binary mixtures, being observed that the preferential solvation occurs in all the studied cases. Finally, studies were performed to investigate the interaction of the dyes with cyclodextrins (CDs). It was possible to observe in some cases a bathochromic shift of the solvatochromic band of the dye and the formation of inclusion complexes between the dye and the CD, indicating the transfer of the dye from a polar, hydrophilic, to another less polar microenvironment, related to the cavity of the CD.