Hybrid rod-like and bent-core liquid crystal dimers exhibiting biaxial smectic A and nematic phases

Abstract

Liquid crystal hybrid dimers involving bent-core units and rod-like units were designed, synthesized and investigated by a combination of polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction studies. All the four unsymmetrical dimers 1-4 exhibited stable nematic phases over a wide temperature range. Moreover, dimer 1 exhibited the biaxial smectic A (SmA) phase and dimer 2 exhibited a highly ordered mesophase below the nematic (N) phase. Two rodlike and bent-core nematogenic units were covalently linked in dimers 3 and 4 to furnish exclusively the nematic phase. The observation of the biaxial SmA phase underlying the nematic phase in one of the bent-core-rod dimers 1 would be a significant step forward towards achieving the biaxial nematic phase and resolving controversies related to the presence of cybotactic groups.

Liquid crystal dimers and the twist-bend nematic phase. The preparation and characterisation of the α,ω-bis(4-cyanobiphenyl-4′-yl) alkanedioates

“…In particular, liquid crystal dimers proved to be a rich source of new types of intercalated smectic phases (see, for example,references [8][9][10][11][12]) and, rare and unusual phase transition sequences (see, for example, references [13,14]). More recently, interest has focussed on, for example, their flexoelectric behaviour, [15][16][17] T-and H-shaped dimers, [18][19][20][21] non-alkyl spacers, [22][23][24] cholesterylbased dimers, [25][26][27][28][29][30] discotic dimers, [31][32][33] carbohydrate-based dimers, [34] bent core-calamitic nonsymmetric dimers, [35,36] the effects of linking groups, [37] dimers containing new types of mesogenic units and functionalities, [38][39][40][41][42][43][44][45][46] as well as on higher oligomers. [47][48][49][50] Perhaps the most exciting recent discovery involving liquid crystal dimers, however, has been the observation of nematic-nematic transitions for a small number of odd-membered dimers.…”

Liquid Crystal-Gold Nanoparticle Hybrid Materials

“…Bent-core LC molecules are one fascinating LC class featured by a banana-shaped or bent-core molecular shape which have attracted a great deal of interest for their exciting electro-optical behavior [65,66]. When the bent-core molecule 13 was used (Scheme 4.5), a columnar phase of hybrid GNPs were obtained (Fig.…”

Conoscopic analysis of electric field driven planar aligned nematic liquid crystal

“…In this paper, a conoscopic technique is used to analyze a complete molecular realignment occurring across a nematic liquid crystal (NLC) medium in response to an external electric field. Even though this method has been adapted to characterize the orientation of LC molecules, the demonstration of a continuous transition from planar to homeotropic state through several intermediate states is not reported yet [8][9][10][11][12][13][14][15]. This method can be effectively employed as a detection tool into areas such as liquid crystal based biosensors with immense applications in the field of medical diagnostics.…”