Author
Indudhara Swamy Shashikala
Bio: Indudhara Swamy Shashikala is an academic researcher from Liquid Crystal Institute. The author has contributed to research in topics: Liquid crystal & Mesogen. The author has an hindex of 10, co-authored 12 publications receiving 428 citations.
Papers
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TL;DR: A "peelable banana" is formed when a bent-core molecule is linked to a rodlike mesogen through a flexible aliphatic spacer in this novel low-molar-mass organic system, which displays a transition from a biaxial nematic (N b ) phase to a bIAxial smectic A phase.
Abstract: A "peelable banana" is formed when a bent-core molecule is linked to a rodlike mesogen through a flexible aliphatic spacer. This is an appropriate description of this novel low-molar-mass organic system, which displays a transition from a biaxial nematic (N b ) phase to a biaxial smectic A phase. The illustration gives a schematic representation of the dimeric molecules in the N b phase as well as the corresponding textural and conoscopic patterns obtained.
117 citations
TL;DR: Several optically pure liquid crystal dimers with strong molecular chirality, synthesized by covalently linking an achiral bent-core unit with a bulky pro-mesogenic rodlike chiral entity through a flexible spacer, display amorphous blue phase, smectic phases, and new sequences.
Abstract: Several optically pure liquid crystal dimers with strong molecular chirality, synthesized by covalently linking an achiral bent-core unit with a bulky pro-mesogenic rodlike chiral entity through a flexible spacer, display amorphous blue phase, smectic phases, and new sequences.
98 citations
TL;DR: Several new optically active liquid crystal dimers comprising promesogenic cholesterol and a chiral diphenylacetylene (tolane) segment, covalently linked in an end-to-end fashion through a flexible spacer, have been synthesized and investigated for their mesomorphic behaviour with the aid of optical, calorimetric and X-ray diffraction studies as mentioned in this paper.
Abstract: Several new optically active liquid crystal dimers comprising pro‐mesogenic cholesterol and a chiral diphenylacetylene (tolane) segment, covalently linked in an end‐to‐end fashion through a flexible spacer, have been synthesized and investigated for their mesomorphic behaviour with the aid of optical, calorimetric and X‐ray diffraction studies. Five unsymmetrical dimers, designed on the basis of recent work, involve molecular structural variations of the tolane mesogenic entity with a view to stabilizing a wide thermal range smectic A (SmA) phase featuring the electroclinic effect. Three different chiral chains, namely, (S)‐1‐methylheptyloxy, (S)‐2‐methylbutyloxy, (3S)‐3,7‐dimethyloctyloxy, with or without polar (nitro or fluoro) lateral substituents, were incorporated, while keeping the length (C6) of the spacer constant. As expected, all the dimers exhibited a SmA phase. A few also showed chiral nematic (N*) and/or twist grain boundary and/or chiral smectic C (SmC*) phases. Remarkably, some of these oli...
42 citations
TL;DR: In this article, mesomorphic linear trimers consisting of bent-core and rod-like anisotropic segments are reported. But the mesomorphic trimers are not shown to have a metastable phase.
Abstract: In this article, we report the first examples of mesomorphic linear trimers consisting of bent-core and rodlike anisotropic segments, primarily conceived to explore the possibility of stabilizing optically biaxial mesophase(s), and we briefly review the work carried out in the area of dimers composed of bent-core mesogen(s). Specifically, four C 2 symmetric trimers, which are formed by covalently tethering nematogenic cyanobiphenyls axially at the peripheral ends of a strongly shape-biaxial bent-core mesogen through two identical polymethylene spacers of varying length and parity, have been probed for their phase behavior and compared with those of the closely related oligomesogens. Four alkylene spacers, namely, hexamethylene, heptamethylene, octamethylene, and decamethylene, have been employed with the sole purpose of learning about the correlation between the resulting molecular conformation (shape) and mesomorphism. The optical and calorimetric studies revealed that all of the trimers, contrary to our prediction, display an enantiotropic uniaxial nematic phase over a wide thermal range (>50 °C), whereas the compound possessing a heptamethylene (odd-parity) spacer displays a metastable smectic phase, additionally. The nematic phase seems to have an inclination for the homogeneous alignment. The nematic-isotropic transition temperatures and associated enthalpies display a moderate odd-even effect; the even members show relatively higher values in a manner reminiscent of trimers made of conventional rodlike anisometric segments.
33 citations
TL;DR: The first nonsymmetric liquid crystal dimers, possessing salicylaldimine and cyanobiphenyl rodlike anisometric segments, exhibiting the biaxial smectic A (McMillan) phase unequivocally evidenced by microscopic, conoscopic, calorimetric and X-ray diffraction studies is reported in this article.
Abstract: The first nonsymmetric liquid crystal dimers, possessing salicylaldimine and cyanobiphenyl rodlike anisometric segments, exhibiting the biaxial smectic A (McMillan) phase unequivocally evidenced by microscopic, conoscopic, calorimetric and X-ray diffraction studies is reported.
31 citations
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TL;DR: This review concludes that Etherification without Cyclization and N-Alkylation should be considered as separate science, and the proposed treatment of Etherification with Cyclization as a separate science should be reconsidered.
Abstract: 10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630
909 citations
TL;DR: An overview on the recent developments in the field of liquid crystalline bent-core molecules (so-called banana liquid crystals) is given in this article, dealing with general aspects of the systematisation of the mesophases, development of polar order and chirality in this class of LC systems and explaining some general structure-property relationships.
Abstract: An overview on the recent developments in the field of liquid crystalline bent-core molecules (so-called banana liquid crystals) is given. After some basic issues, dealing with general aspects of the systematisation of the mesophases, development of polar order and chirality in this class of LC systems and explaining some general structure–property relationships, we focus on fascinating new developments in this field, such as modulated, undulated and columnar phases, so-called B7 phases, phase biaxiality, ferroelectric and antiferroelectric polar order in smectic and columnar phases, amplification and switching of chirality and the spontaneous formation of superstructural and supramolecular chirality.
753 citations
TL;DR: In this article, structural and properties of liquid crystalline phases formed by bent-core molecules are reviewed and the most attractive properties of this new class of liquid crystals are in polarity and chirality, despite being formed from achiral molecules.
Abstract: Structures and properties of liquid crystalline phases formed by bent-core molecules are reviewed. At least eight phases designated as B1–B8 have been found, being unambiguously distinguished from phases formed by usual calamitic molecules due to a number of remarkable peculiarities. In addition to B1–B8 phases, smectic A-like phases and biaxial nematic phases formed by bent-core molecules are also reviewed. The most attractive aspects of this new class of liquid crystals are in polarity and chirality, despite being formed from achiral molecules. The bent-core mesogens are the first ferroelectric and antiferroelectric liquid crystals realized without introducing chirality. Spontaneous chiral deracemization at microscopic and macroscopic levels occurs and is controllable. Moreover, achiral bent-core molecules enhance system chirality. The interplay between polarity and chirality provides chiral nonlinear optic effects. Further interesting phenomena related to polarity and chirality are also reviewed.
713 citations
TL;DR: The underlying theme of this Critical Review is the relationship between molecular structure and liquid crystalline behaviour in a class of materials referred to as liquid crystal oligomers, and how this molecular architecture has been exploited to address issues in a range of quite different areas and has given rise to potential applications for these materials.
Abstract: The underlying theme of this Critical Review is the relationship between molecular structure and liquid crystalline behaviour in a class of materials referred to as liquid crystal oligomers. For the purposes of this review, a liquid crystal oligomer will be defined as consisting of molecules composed of semi-rigid mesogenic units connected via flexible spacers. Much of the review will be devoted to structure–property relationships in the simplest oligomers, namely dimers, in which just two mesogenic units are connected by a single spacer. Along the way we will see how this molecular architecture has been exploited to address issues in a range of quite different areas and has given rise to potential applications for these materials. On the whole, only compounds in which the mesogenic units are linked essentially in a linear fashion will be considered while structures such as liquid crystal dendrimers and tetrapodes fall outside the scope of this review. The review will be of interest not only to scientists working directly in this area but in particular to those interested in understanding the relationships between structure and properties in polymers, and those designing materials for new applications (231 references).
465 citations
TL;DR: An overview of the current state of research in the field of biaxial nematic liquid crystalline materials is given in this paper, where the major theoretical concepts are outlined, including the classification to different symmetries, the importance of cooperativity and cluster formation for the development of BN order and the conditions for the establishment of field induced and spontaneous BN in nematic phases.
Abstract: An overview over the current state of research in the field of biaxial nematic liquid crystalline materials is given. After a short introduction, providing some general aspects and summarizing the classical approaches, the main part focuses on recent developments of new concepts for designing biaxial nematics. First, the major theoretical concepts are outlined, including the classification to different symmetries, the importance of cooperativity and cluster formation for the development of biaxial order and the conditions for the establishment of field induced and spontaneous biaxiality in nematic phases. These new concepts also require the re-evaluation of the tools used for the identification of phase biaxiality, which are discussed briefly. In the second part, recent progress in the design of potential biaxial nematic materials, especially focussing on bent-core molecules with nematic phases, is reported and, finally, comparisons with phase biaxiality as observed in smectic liquid crystals are made.
299 citations