Dimers of the columnar mesomorphic 2-substituted benzene-1,2,5,-tricarboxamide (BTA) unit: study of the liquid crystallinity in the bulk and of the self-assembly in solution

The self-assembly of <i>N</i>, <i>N’</i>, <i>N’’</i>-trialkylbenzene-1,3,5-tricarboxyamides (BTAs) has been reported to lead to supramolecular columnar-stacked structures with attractive material properties. The formation of the columnar liquid crystalline phases (mesophases) along a broad range of temperature is one of the most interesting properties shown by BTAs. In this thesis, the formation of dimeric structures from the BTA unit was carried out to investigate the stabilization effect on the columnar supramolecular aggregation. <br> The first challenge concerned the functionalization of the BTA scaffold in order to introduce an “anchoring site” and achieve the formation of dimers. In this context, in the literature, the introduction of alkoxy groups has been demonstrated to reinforce the self-assembly process. For this reason, we synthetized a mono-2-substituted BTA carrying a pentynyloxy group. We investigated the aggregation process of the newly synthetized 2-substituted BTAs in the bulk and in solution by means of DSC, POM, X-ray diffraction and concentration-induced ¹H-NMR experiments. The presence of this single substituent significantly influenced the self-assembly process. Moreover, those measurements revealed that the self-assembly was impaired by H-bond accepting substituents and strengthened by non-H-bonding substituents. <br> In the second part, the 2-substituted BTA derivative was employed in the construction of covalently-connected dimers. The study of the self-assembly process of the dimers was carried out in solution by employing concentration-induced NMR analyses. These measurements revealed the enhancement of the association process upon dimerization. However, none of the dimeric structures presented liquid crystallinity. Therefore, we synthetized a library of 2-substituted BTA dimers with different aromatic linkers and modifications on the amide side-chains. Finally, we screened the ability of these dimeric compounds to form mesophases with the goal of establishing an empirical structure-properties relationship.

Thèse de doctorat : Université de Neuchâtel, 2015