Molecular shape is an important factor in determining the material properties of thermotropic liquid crystals (LCs). We synthesized and investigated several LC compounds formed by asymmetrically bent molecules with a rigid four-ring core in the shape of the letter ‘L’. We measured the temperature dependencies of dielectric permittivities, birefringence, splay K₁ and bend K₃ elastic constants, splay viscosity η_splay and flow viscosities η_|| and η_⊥. The bend–splay anisotropy δK₃₁ = K₃ − K₁ is negative, similar to the case of nematic LCs formed by symmetrically bent molecules of V-shape. The dielectric anisotropy Δε and birefringence are positive in the entire nematic range. The splay viscosity η_splay and the flow viscosities η_|| and η_⊥ are smaller than the viscosities measured for the symmetric V-shaped bent-core materials at similar temperatures. The ratio Γ = η_splay/η_||,⊥ is in the range 5–4 that is typical for rod-like LCs. The reported L-shaped bent-core nematic LCs combine the useful features of bent-core LCs (such as a negative δK₃₁, suitable for formulation of broad-range blue phases) with the relatively low viscosities, a property typical for rod-like LCs and beneficial for electro-optic switching applications.

Achiral molecules based on a novel four-ring core with an ester linkage at the molecular bend are shown to exhibit smectic liquid crystal phases with spontaneously chiral and polar layers (SmCP phases), including their polarization splay modulated and layer undulated (PMLU) variants, B7 and B1. Additionally, these compounds exhibit strong photoluminescence, the first family of SmCP phases to do so.

In a newly designed four-ring asymmetrical bent-core compound, we observed smectic-C-type diffuse layer reflection over the entire nematic temperature range. At the nematic–smectic C phase transition, a sharp layer reflection emerges in addition to the diffuse reflection with different layer tilt angles.

New lanthanide complexes, Tb(III), Dy(III) and Gd(III) of N-aryl based Schiff bases exhibiting mesomorphism have been synthesised and characterised. The crossover phenomena of calamitic lamellar to discotic columnar phase behaviour in these lanthanidomesogens is found to be controlled by the variation in chain length of the single alkyl substituent on the terminal N-aryl ring, hitherto the first case of a metallomesogen with only one alkyl chain length at each end of the ligand as evidenced by thermal microscopy studies and complemented by X-ray studies. It is also observed as a function of temperature in a single component. The electronic properties of these systems are dominated by the donor–acceptor substituted organic chromophore ligand, and the emission maxima revealed a large Stokes shift of 160 nm. The ligand–ligand charge transfer is reflected in emission spectra and is due to the presence of phenyl rings in the ligands.

The synthesis of new mononuclear and binuclear copper complexes derived from Schiff bases, namely N(4-n-alkyloxysalicylidene)-4′-n-alkylanilines is carried out and their structure and liquid crystalline properties have been investigated. The ligands exhibit rich polymesomorphism; mononuclear complexes exhibit smectic A, smectic C and smectic E phases, while the binuclear complexes mostly exhibit viscous smectic A phase. The isotropic–liquid crystalline transition temperatures of the binuclear complexes in general are found to be lower than their corresponding mononuclear homologues. It was found that the mononuclear complexes exhibit sharp liquid crystalline–isotropic transition temperatures while the binuclear complexes melts over a temperature range. The liquid crystalline phases were characterised by differential scanning calorimetry (DSC) analysis and optical polarised microscopy. X-ray diffraction studies revealed that the intermolecular distance in binuclear complexes is larger than in the mononuclear complexes.

Single-walled carbon nanotubes (SWCNTs) are dispersed in (4’-fluoro phenyl azo) phenyl-4-yl 3-[N-(4’-n-hecyloxy 2-hydroxybenzylidene)amino]-2-methylbenzoate (6–2M-F) a bent-core nematic (BCN) liquid crystalline medium composed of bent-shaped molecules with short core, reduced bend angle possessing polar fluoro substituent in longitudinal direction and methyl group in bent direction. Such molecules are at the borderline of typical bent-core and rod-like molecules resembling hockey stick shape with intermediate properties. The elastic anisotropy is negative for 6–2M-F (bend elastic constant K₃₃ < splay elastic constant K₁₁); similar to other BCNs reported earlier with smectic-like clusters; but turns to high positive (K₃₃ > K₁₁) value by insertion of SWCNT (concentration ≥0.05 wt.%) in 6–2 M-F. The ratio of K₃₃/K₁₁ becomes comparable to the calamitic liquid crystals (LCs) in doped system. Dielectric anisotropy increases in the nanocomposite implying enhanced nematic ordering due to π–π electron interaction between CNTs and the LC molecules. Threshold voltage at first increases and then decreases with increasing CNT concentration owing to the respective variations in splay viscosity of the system. The present study demonstrated the interaction of SWCNTs with BCN molecules and reveals significant modifications in viscoelastic, dielectric and ionic properties of the host. Graphical Abstract