Synthesis and Liquid Crystalline Properties of Low Molecular Weight Bis-Chalcone Compounds

Aims: In this paper, we report on the synthesis and liquid crystalline properties of some low molecular weight bis-chalcone compounds derived from acetone, cyclopentanone and cyclohexanone mesogenic cores. Background: Structurally bis-chalcones belong to a broader family of chalcone compounds. Chalcone is a compound that consists of two aromatic rings linked by an unsaturated alpha, beta-ketone. Objective: Liquid crystalline chalcones are prepared by aliphatic chain substituents on two aromatic rings. Chalcones are well studied for their mesomorphic properties. Compared to a large number of chalcone based LCs reported, only a few articles have been published on the mesomorphic properties of bis-chalcone compounds. The target compounds of the present study varied not only in their central core but also in number and position of terminal aliphatic chain substitution-a key structural unit in deciding the liquid crystalline properties of a compound. Methods: All target compounds were synthesized in good yield by base catalyzed Claisen-Schmidt condensation reaction. Molecular structures were confirmed by FT-IR, H-1 NMR, C-13 NMR, and mass spectroscopic methods. Liquid crystalline property of these compounds was evaluated using polarizing optical microscopy and differential scanning calorimetry. Results: Although none of the acetone based compounds exhibited mesomorphism, cyclopentanone and cyclohexanone based compounds with octyloxy chain at para position on either side of the dibenzylidine ring stabilized liquid crystalline smectic (SmA and SmC) and nematic (N) phases. The observed structure-liquid crystalline property relationship was explained by structural analysis of molecules using DFT calculations. Considering the inherent photoluminescence nature of the chalcone moiety, a preliminary study was carried out on a selected compound to reveal its fluorescence property. Conclusion: Our study brings about an important structure-liquid crystalline property relationship in a relatively unexplored class of bis-chalcone liquid crystals.