Synthesis, characterization and mesomorphic investigations of ester-substituted aroylhydrazones possessing a lateral hydroxyl group

The synthesis, characterization and investigation of a new liquid crystalline series of ester containing aroylhydrazones with a lateral hydroxyl group, N-[4-(4′-alkoxy)benzoyloxy-2-hydroxy-benzylidene]-N′-[4″-alkoxybenzoyl]hydrazine (Cm,nLH), with the same or different peripheral alkoxy chains, and some of their nickel(II) and copper(II) complexes are described. All the ligands, except those with no terminal chains on either end of the molecule, exhibit an enantiotropic SmC mesophase, as evidenced by polarizing optical microscopy and differential scanning calorimetric studies. It has been found that addition of a lateral hydroxyl group along with ester-substitution to the aroylhydrazone core increases the mesomorphic as well as thermal stability of the ligands. Also, the coordination of Ni2+ and Cu2+ with the aroylhydraozone core inhibits the mesomorphic potential of the ligands. A temperature dependent Raman study of one of the members, C12,12LH (m = n = 12) has been made to identify phase transitions and to understand the molecular rearrangement as a result of changes in intermolecular interactions at the phase transition. DFT calculations have been performed to obtain the stable electronic structure of the ligand (C6,6LH) and its nickel(II) complex.

Graphical abstractThe synthesis, characterization and mesomorphic investigations of a new series of ester containing benzylidene-hydrazines with a lateral hydroxyl group, Cm,nLH, with the same or different peripheral alkyl chains, and some of their nickel(II) and copper(II) complexes are described. A temperature dependent Raman study was employed to understand the molecular rearrangement of the molecules during the phase transitions.Figure optionsDownload full-size imageDownload as PowerPoint slide