Coumarin Schiff base-esters liquid crystals with symmetrical and unsymmetrical alkoxy chains: Synthesis, mesomorphic properties and DFT approach

Improving the mesomorphism in bispyrazolate Pd(II) metallomesogens: an efficient platform for ionic conduction

The introduction of structural asymmetry in metallomesogens is an established strategy to improve their mesomorphic behaviour in terms of lower melting temperatures and higher stability ranges of the mesophase, which is particularly important for metallomesogens that have potential application as electrolytes that require wide operational temperature ranges. Here in this work, a novel series of unsymmetrical bis(isoquinolinylpyrazolate)palladium(II) compounds bearing four alkyl side-chains with different lengths are described. Rectangular and hexagonal columnar mesophases were formed with low melting temperatures of 42-45 °C in most cases, whereas the clearing temperatures reached values up to 412 °C. The charge transport properties have been studied by complex impedance spectroscopy, showing that the mesophase favours proton conduction in the absence of water or humidity. The exceptional thermal stability of these species makes them promising candidates to act as a platform for ionic conduction via the nanochannels originated in the columnar mesophases. The results presented confirm that introducing structural asymmetry in the Pd(II) metallomesogens studied is a valid strategy to enhance the liquid crystalline properties, which opens new ways to develop water-free electrolytes based on unsymmetrical bis(isoquinolinylpyrazolate) Pd(II) compounds for potential applications such as proton exchange membranes (PEMs).

Novel Imidazole Liquid Crystals; Experimental and Computational Approaches

The liquid crystalline materials named (E)-4-(2-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)hydrazineylidene)methyl)phenyl and 4-(alkoxy)benzoate, In, were synthesized and their mesomorphic behaviors were examined. The chemical structures of the produced compounds were confirmed by Fourier-transform infrared spectroscopy (FT-IR), NMR, and elemental analysis. Differential scanning calorimetry (DSC) and polarized optical microscopy were used to investigate the mesomorphic properties of designed heterocyclic derivatives. All the compounds tested had suitable thermal stability and enantiotropic behavior of smectogenic temperature ranges. Furthermore, the enantiotropic smectic C phases were observed to cover all the homologues. Moreover, computational investigations corroborated the experimental findings of the mesomorphic behavior. The reactivity parameters were computed for the derivatives and linked with the experimental data. Theoretical calculations revealed that the polarizability of the studied series increases with the chain length, whereas the HOMO–LUMO energy gap or other reactivity descriptors were less sensitive to the size of the system. On the other hand, the predicted thermodynamic parameters revealed the size dependence of thermal stability of the compounds.