Several first- or second-generation Janus-type codendrimers that combine promesogenic bent-core and rodlike molecular segments have been synthesized by the versatile CuAAC reaction and the materials have been characterized by POM, DSC, XRD, and SHG studies. Depending on the ratio between the number of rod- and bent-core units, these compounds form mesophases ranging from nematic to a complex polar smectic mesophase in which the two types of mesogenic moieties are segregated on a nanometric scale. In the case of a 1:1 bent/rod ratio, the materials form ferroelectric mesophases and the macroscopic polarization is stable in the absence of an applied electric field. The appearance of the different mesophases is explained in terms of the relative values of the transverse areas of the mesogenic cores.

A laterally azo-bridged trimer ferroelectric liquid crystal (FLC) incorporating a strong chromophore along its polar axis was synthesized and characterized by polarized-light optical microscopy, differential scanning calorimetry, two-dimensional X-ray diffraction analysis, electro-optical measurements, and nonlinear optical (NLO) investigations. This mesogen exhibits a thermodynamically stable enantiotropic SmC* phase and a bistable ferroelectric switching in a surface stabilized cell with bookshelf geometry. It gives the resonance-enhanced d(22) coefficient of 28 pm V-1 (lambda = 1.369 mu m) for second harmonic generation (SHG), the largest NLO susceptibility reported to date for all FLCs. At the same wavelength, a new type of helicoidal phase matching assisted by the helical SmC* structure was identified. When the second harmonic wavelength of 780 nm is far away from the resonance wavelength (lambda(max) = 572 nm), the d22 coefficient is reduced to 6.8 pm V-1 (lambda = 1.56 mu m). In addition to a strong SHG activity, the trimer also shows a strong third harmonic generation (THG) with an estimated third-order nonlinear susceptibility of chi((3)) = similar to 3 x 10(-11) esu (lambda = 1.56 mu m), among the largest chi((3)) value reported from THG measurements for liquid crystals. This work enables viable applications of FLCs in nonlinear optics and offers an innovative approach to develop new FLCs with larger NLO strength.

Three series of bent-shaped compounds containing the 1,2,3-triazole ring in the central core of the molecule have been prepared by the most extended “click chemistry” reaction, the copper-catalyzed azide-alkyne cycloaddition (CuAAC). This research demonstrates the versatility of this synthetic approach with the aim of achieving innovative compact supramolecular organizations. The appropriate combination of the 1,2,3-triazole synthon linked either to a methylene unit (series M) or to a methylenoxycarbonyl block (series MC) has allowed the induction of a variety of non-classical bent-core liquid crystal phases versus the classic mesophases promoted by 1,4-diphenyl-1,2,3-triazole derivatives (series T). Through a suitable selection of common lateral structures connected by “click chemistry” both the transition temperatures and mesomorphism, ranging from lamellar to columnar or B4-like supramolecular liquid crystalline organizations, can be tuned.