Designed new mesogens via Vilsmeier-Haack reagent: synthesis and phase transition study

A new four series of 2,2 '-([1,1 '- phenyl or biphenyl]-4,4 '-diylbis(azanediyl)) bis(N '-((E)-1-(4-alkoxyphenyl) ethylidene) acetohydrazide) [V-XI](a,b) and 1,1 '-(2,2 '-([1,1 '- phenyl or biphenyl]-4,4 '-diyl bis(azanediyl)) bis- (acetyl)) bis(3-(4-ethoxyphenyl)-1H-pyrazole-4-carbalde hyde) [XII-XVIII](a,b) have been synthesized by varying terminal lateral alkoxy chain length (n = 1-3, 5-8), central linkage group (phenyl or biphenyl) and induced pyrazole heterocyclic ring in the main chain. The last two series were synthesized by the cyclization of substituted acetophenone hydrazones with Vilsmeier-Haack reagent (DMF/POCl3) to produce 4-formylpyrazole derivatives. The chemical structures of the synthesized compounds were examined by elemental analysis, FTIR and H-1-NMR. The results are in agreement with the considered molecular structure. The liquid crystalline behaviors were studied by using hot-stage optical polarizing microscopy (OPM) and differential scanning calorimetry (DSC). The correlation between the molecular structures and mesomorphic behavior and transition temperatures was discussed.

Automated summary

A new series of compounds were synthesized by varying side chain structure and heterocyclic ring in the main chain, and their chemical structures and liquid crystalline behavior were studied.