Experimental and Computational Study of Thiophene Based Calamitic Liquid Crystals

Abstract

The structurally analogous calamitic mesogens 4-((4-(decyloxy) phenoxy) carbonyl) phenyl thiophene-2-carboxylate [2TWC10] and 4-(Thiophen-3-yl) phenyl 4-dodecylbenzoate [S12] based on thiophene were synthesized and structures of the molecules were confirmed by spectroscopic techniques. Among the two molecules, only 2TWC10 mesogen with alkoxy terminal exhibited a typical threaded structure indicating a homeotropic nematic phase under hot stage-polarizing optical microscopy (HOPM). Further, it is supported by differential scanning calorimetry (DSC). Remarkably, alkyl terminal S12 mesogen is not showing liquid crystalline properties. This is because S12 has alkyl group as the terminal group instead of alkoxy group which was used generally, resulting in bent shape to the molecule which reduced aspect ratio which is essential for liquid crystalline property. UV-Visible absorption maxima because of - transitions in these mesogens were found at280-300 nm in chloroform solution. The DFT study shows that the alkoxy terminal in 2TW10 is contributing to polarity of the molecule but in S12 there is no contribution from terminal chain because it is non polar group. The DFT study also shows that 2TWC10 is more reactive and less stable than S12 molecule.