Sulfonamide Linked Diacylhydrazine Based Calamitic Liquid Crystals: Synthesis, Characterization, and Mesomorphic Studies

Abstract

Calamitic liquid crystals have been used by researchers due to their efficient anisotropic properties and appearance of different phases. These liquid crystals are widely used in display technology and in the formation of supramolecular polymers. In calamitic LCs, mesophase stability is due to rigid core and terminal chain length. Moreover, sulfonamides and diacylhydrazine linkages attained attention due to thermal stability and mesomorphic behavior. Keeping in view the vast applications of phenyl and biphenyl based amides and sulfonamide linked LCs, and also the effect of rigid core on mesomorphic behavior, two series of sulfonamide linked diacylhydrazines (VIlla-g) were designed. The two series, N-( 4-(2-( 4-( alky loxy) benzoy 1 )hydrazine-l -carbony 1 )pheny 1 )-4-methy 1 benzene sulfonamide (Villa-c) and N-( 4-(2-( 4/ -( alkyloxy)-[ 1,1/ -biphenyl]-4-carbonyl) hydrazine-l-carbonyl)phenyl)-4-methylbenzenesulfonamide (VIlld-g) were prepared via multistep sequence starting from the esterification of 4-hydroxy aryl carboxylic acids (Ia,b) to its corresponding esters (lIa,b) followed by its treatment with different alkyl halides to yield alkylated esters (IlIa-k). Ester functionality was converted to corresponding hydrazides (IVa-j) on treatment with hydrazine hydrate. 4-(4-Methyl phenylsulfonamido )benzoic acid (VII) was obtained by the reaction of p -aminobenzoic acid with p-toluenesulfonyl chlorides. In the final step, alkoxy hydrazides were coupled with 4-( 4-methylphenylsulfonamido )benzoic acid to get the target molecules (VIlla-g). Rise in melting temperature from phenyl to biphenyl rigid core indicated the increase in stability of molecules. The structural characterization of all the synthesized compounds was carried out engaging IH and I3C-NMR spectroscopy. Liquid crystalline properties of some of the synthesized derivatives were confirmed employing differential scanning calorimetry (DSC).