We report the design, synthesis, detailed characterization, and analysis of a new multifunctional π-conjugated bola-amphiphilic chromophore: oligo-(p-phenyleneethynylene)dicarboxylic acid with dialkoxyoctadecyl side chains (OPE-C-1). OPE-C-1 shows two polymorphs at 123 K (OPE-C-1') and 373 K (OPE-C-1″), whose crystal structures were characterized via single crystal X-ray diffraction. OPE-C-1 also exhibits thermotropic liquid crystalline property revealing a columnar phase. The inherent π-conjugation of OPE-C-1 imparts luminescence to the system. Photoluminescence measurements on the mesophase also reveal similar luminescence as in the crystalline state. Additionally, OPE-C-1 shows mechano-hypsochromic luminescence behavior. Density functional theory (DFT)-based calculations unravel the origins behind the simultaneous existence of all these properties. Nanoindentation experiments on the single crystal reveal its mechanical strength and accurately correlate the molecular arrangement with the liquid crystalline and mechanochromic luminescence behavior.

Existing liquid crystal (LC) smart window technologies are yet to make inroads into the consumer market largely due to more than 50% of the cost-share by the tin-doped indium oxide...

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We report the influence of photoisomerization on a guest-host composite comprising a soft-bent dimer exhibiting the presently sought-after twist-bend nematic (NTB) phase, doped with small amounts of a calamitic photoactive azobenzene-based dimer that assumes a bent shape when photo-driven. Trans-cis photoisomerization of the latter compound leads to a substantial decrease in the nematic-isotropic and nematic-NTB transition temperatures. The results bring out the puzzling feature that the thermal stability of the NTB phase, having a helical structure, despite the molecules being achiral, is influenced more than the regular nematic. Differential influence is also seen in the Frank elastic constants of the regular nematic: while the splay elastic constant is significantly diminished its bend counterpart is hardly affected. Molecular conformational aspects of the entities are proposed to explain these features. Through a judicious combination of this photo-driven effect and an AC electric field, an attractive type of optical memory device is demonstrated.

We report the influence of photoisomerization on the splay (K11) and bend (K33) elastic constants in a bent-core nematic doped with a small amount of a calamitic photoactive compound. Trans-cis isomerization of the latter compound results in a large decrease (factor of ∼3 for K33) of both the moduli, and K33 becoming almost independent of temperature except near the isotropic phase. The observed variations are much larger than can be explained by order parameter changes, and are explained using an argument based on the molecular arrangement.