Synthesis, thermal stabilities, and anisotropic properties of some new isoflavone-based esters 7-decanoyloxy-3-(4'-substitutedphenyl)-4H-1-benzopyran-4-ones

A series of new isoflavonic esters 7-decanoyloxy-3-(4'-substitutedphenyl)-4H-1-benzopyran-4-ones containing a heterocycle in their central core with one flexible alkyl chain and various substituents, R (where R=F, Cl, Br, CH3, OCH3, or H) at 4'-position at one end, have successfully been synthesised, isolated, and characterised. The physical properties of title compounds were studied using spectroscopic techniques (Fourier transform infrared, 1H and 13C nuclear magnetic resonance). The liquid crystalline properties and the textures of these compounds along with their thermal stabilities were investigated via polarising optical microscopy and differential scanning calorimetry. All the compounds except the member without the substituent were enantiotropic mesogens exhibiting smectic A and/or nematic phases. The layer periodicities in relation to different phases were substantiated by X-ray diffraction wherein the molecules within the SmA phase were found to be intercalated. The structural changes that resulted in a variation of transition temperature as well as the electronic polarisability of the respective compounds are also discussed.