New thiophene chalcones with ester and Schiff base mesogenic Cores: Synthesis, mesomorphic behaviour and DFT investigation

Abstract

• Thiophene chalcones possessing Schiff base and ester mesogenic core have been synthesized. • Enantiotropic nematic (N) and Smectic A (SmA) phases were observed. • The impact of various connecting units, phenyl rings and of alkoxy chain length has been investigated. • Comparison with structurally similar compounds has been studied. • The DFT calculations of the thermodynamic and dimension parameters were conducted and correlated to mesomorphic behaviour. A new homologous series of thiophene-based mesogens, 4-((E)-((4-((E)-3-(thiophen-2-yl)acryloyl)phenyl)imino)methyl)phenyl-4-(alkyloxy)benzoate, TE- ( 2 – 18 ) in which thiophene heterocyclic unit at one end and long terminal alkoxy chains (C2-C18) at the other end were synthesized, characterized and studied for their mesomorphic and thermal behaviour. Differential scanning calorimetry (DSC) was used to investigate the phase transitions whereas types of mesophase were confirmed by polarized optical microscopy (POM). The mesomorphic investigation revealed that all new derivatives TE-(2 – 14) displayed an enantiotropic nematic phase (N) except the longer alkoxy chain ( n = 16 and 18) which are dimorphic in nature exhibited enantiotropic smectic A phase (SmA) in addition to enantiotropic nematic (N) phase. The mesomorphic behaviours of the new mesogens were investigated and discussed thoroughly and further compared with structurally similar compounds. Further, the optimised geometry of thiophene mesogens has been theoretically derived by the density functional theory (DFT) and the results revealed none co-planar structures for all compounds. The relationships between the calculated parameters, the polarizability, dimension parameters, have been used to illustrate the mesomorphic properties either the type of the texture or the mesomorphic range and stability.