Showing papers by "D. S. Shankar Rao published in 2018"
TL;DR: In this paper, a series of flying bird-shaped liquid crystalline (LC) cyanopyridone derivatives with a D-A-D-D architecture, CPO-1 toCPO-4, have been designed and synthesized.
Abstract: Herein, we report the design and synthesis of a new series of flying bird-shaped liquid crystalline (LC) cyanopyridone derivatives with a D–A–D architecture, CPO-1 to CPO-4. Their mesomorphic, photophysical, electrochemical, and electroluminescence characteristics have been investigated in detail. Here, the H-bonding interactions through a central lactam core were shown to be the key driving force for their self-assembly into columnar mesophases. The key role of H-bonding has been confirmed by using newly synthesized similar shaped compounds, MCP-1 to MCP-3. New CPO mesogens were found to be intense greenish blue light emitters with narrow band-gap energies. Conclusions were drawn based on theoretical studies also. Finally, the application potential of the selected mesogen CPO-2 as an emissive material has been demonstrated for the fabrication of doped and non-doped OLED devices with different device architectures, which displayed encouraging results. In fact, this is the first report on the use of emissive H-bond-assisted columnar liquid crystals in devices. The present results provide a new guideline and a versatile approach to the design of new LC molecules for the fabrication of efficient OLEDs.
19 citations
TL;DR: It is reported here that a small concentration of CNTs doped to a "nematic mesophase-only" material not only induces the layered smectic A mesophases but also leads to the nematic-smectic-nematically re-entrant sequence as well, demonstrating the delicate interplay between the two entities.
Abstract: Although representing drastically different chemical natures and types of interactions, the similarity of shape anisotropy of the constituents has created much interest in composites of calamitic l...
13 citations
20 Apr 2018
TL;DR: The effect of the number and positions of alkoxy chains on the self-assembly induced physical properties of a few π-conjugated molecules is reported.
Abstract: Rational understanding of the structural features involving different noncovalent interactions is necessary to design a liquid crystal (LC) or an organogelator. Herein, we report the effect of the number and positions of alkoxy chains on the self-assembly induced physical properties of a few π-conjugated molecules. For this purpose, we designed and synthesized three C3-symmetrical molecules based on oligo(p-phenylenevinylene), C3OPV1–3. The self-assembly properties of these molecules are studied in the solid and solution states. All of the three molecules follow the isodesmic self-assembly pathway. Upon cooling from isotropic melt, C3OPV1 having nine alkoxy chains (−OC12H25) formed a columnar phase with two-dimensional rectangular lattice and retained the LC phase even at room temperature. Interestingly, when one of the −OC12H25 groups from each of the end benzene rings is knocked out, the resultant molecule, C3OPV2 lost the LC property, however, transformed as a gelator in toluene and n-decane. Surprisin...
12 citations
06 Jul 2018
TL;DR: In this paper, a dual-frequency liquid crystal (DFLC) was used for full Stokes polarimetery and a polarization modulator has been worked out based on two DFLCs and two static retarders.
Abstract: In a dual-frequency liquid crystal (DFLC), when the frequency of the applied voltage is more than a critical value (fc), the dielectric anisotropy of the material changes from positive to negative. This causes the director to switch its orientation from parallel to the field (for f < fc), to perpendicular to it (f < fc). Hence DFLC can be used in modulating the light by switching the frequency of an externally applied voltage. We present in this work about application of DFLCs in full Stokes polarimetery. A polarization modulator has been worked out based on two DFLCs and two static retarders. The combination of DFLCs’ switching and static retarders are chosen such that more or less equal weightage is given to all the Stokes parameters. Initial results on the optimization of position angles of the modulators are presented towards the goal of achieving polychromatic modulator in the wavelength range 600-900 nm.
3 citations
TL;DR: In this paper, the authors present results on the regular nematic phase of a binary mixture comprising such a soft-bent dimer, known in the literature as CB7CB, by incorporating zinc oxide nanorods (NRs) into the system.
Abstract: Bent-core liquid crystals (LCs) introduced a whole new dimension to the science of LCs. Besides re-emphasizing the importance of the shape of the molecule, they brought in phases with symmetry, not known earlier. Another sub-class of systems that is emerging is that of soft-bent molecules. In contrast with the bent-core molecules, here the bend is achieved through the parity of the aliphatic linker that connects two monomers. They hold the unique advantage that a simple variation of temperature can favour different conformer states and thus govern the self-assembled structure. A highlight of the power of this route is seen in terms of the discovery of a new type of nematic, viz., twist–bend nematic. Investigations on not only this phase but also the regular nematic that often precedes it have received significant attention in the last few years. Here we present results on the regular nematic phase of a binary mixture comprising such a soft-bent dimer, known in the literature as CB7CB, by incorporating zinc oxide nanorods (NRs) into the system. The NRs with an aspect ratio of $${\sim }$$
7.2, not very different from that of LCs, further accentuate the importance of shape and shape anisotropy of the entities. Specifically, we observe that the nematic–isotropic transition temperature increases by $${\sim }$$
1.9 K even for a low concentration of 4% NRs. While the dielectric anisotropy decreases, birefringence shows a substantial increase, adding to the complexity of the influence. Upon addition of minute amount of NRs (1%), while the splay elastic constant gets enhanced, its bend counterpart not only gets reduced but retains the convex-shaped thermal profile seen for the parent mixture.
2 citations
TL;DR: In this article, a dual-frequency liquid crystal (DFLC) is used to switch the orientation from parallel to the field (for $f f f c$) in order to achieve a polychromatic modulator in the wavelength range 600-900 nm.
Abstract: In a dual-frequency liquid crystal (DFLC), when the frequency of the applied voltage is more than a critical value ($f_c$), the dielectric anisotropy of the material changes from positive to negative. This causes the director to switch its orientation from parallel to the field (for $f f_c$). Hence DFLC can be used in modulating the light by switching the frequency of an externally applied voltage. We present in this work about application of DFLCs in full Stokes polarimetery. A polarization modulator has been worked out based on two DFLCs and two static retarders. The combination of DFLCs' switching and static retarders are chosen such that more or less equal weightage is given to all the Stokes parameters. Initial results on the optimization of position angles of the modulators are presented towards the goal of achieving polychromatic modulator in the wavelength range 600-900 nm.
2 citations