Desenvolvimento de moléculas discóticas baseadas em azobenzenotetraésteres alquílicos

Abstract

Functional organic materials are resources widespread in the scientific and technological environment for having employability in several areas. In particular, liquid crystals (LCs) offer the development of new dynamic materials, they have unique electro-optical properties allied with fluidity and molecular order. In this context, this work presents the synthesis, characterization and study of the thermal and hotophysical properties of twelve compounds, whose molecules were designed to have discotic structures derived from alkyl tetra-esters of azobenzene to generate liquid-crystalline phases. Characteristics of self-assembly and selforganization common to LCs would be controlled by the insertion of the azo group, performing “on-off” role of the properties like the optical switch, due intrinsic reversible photoisomerization effect E-Z-E, in the presence of radiation in the UV-Vis region. The molecule chosen as the base of the discoid compounds was azobenzene-3,3', 5,5'- tetracarboxylic acid, because it has carboxylic groups directly connected to the aromatic system, these capable of being converted into other groups, besides the presence of the azo photoresponsive group on center, aiming to add character fluidity, alkyl chains were incorporated into the center using Fischer esterification reactions, using linear and branched chain aliphatic alcohols. To understand the relationship between the structure and the physical-chemical behaviour exhibited by the materials containing a variety of alkyl groups. The final compounds were characterized by 1H and 13C nuclear magnetic resonance (NMR), spectroscopy in the infrared region (IV) e mass spectrometry (MS). Photo-induced isomerization properties of the azo group were studied in solution by UV-Vis absorption spectroscopy. Thermal behaviour was evaluated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and polarized light optical microscopy (MOLP). The alkyl chains promoted different degrees of fluidity to the compounds, which reflects in the decrease of the melting points due to increase in the size and number of carbons of the chains. The branched chain compounds have a greater hysteresis interval, when compared to their isomers of linear chains. However, none generated liquid-crystalline phase. The optical study confirmed the photoisomerization property of the azo group of the compounds in solution.