Ru(II) polypyridine complexes: photophysics, photochemistry, eletrochemistry, and chemiluminescence

About Supramolecular Assemblies of π-Conjugated Systems

Most associate liquid crystals with their everyday use in laptop computers, mobile phones, digital cameras, and other electronic devices. However, in contrast to their rodlike (calamitic) counterparts, first described in 1907 by Vorlander, disklike (discotic, columnar) liquid crystals, which were discovered in 1977 by Chandrasekhar et al., offer further applications as a result of their orientation in the columnar mesophase, making them ideal candidates for molecular wires in various optical and electronic devices such as photocopiers, laser printers, photovoltaic cells, light-emitting diodes, field-effect transistors, and holographic data storage. Beginning with an overview of the various mesophases and characterization methods, this Review will focus on the major classes of columnar mesogens rather than presenting a library of columnar liquid crystals. Emphasis will be given to efficient synthetic procedures, and relevant mesomorphic and physical properties. Finally, some applications and perspectives in materials science and molecular electronics will be discussed.

Discotic Liquid Crystals: From Tailor-Made Synthesis to Plastic Electronics

This critical review begins with a brief, but essential, introduction to the special nature of liquid crystal materials, their peculiar properties, and their commercial applications, followed by an introductory insight into the remarkable nature of the fluoro substituent, and its fascinating influence on the properties of organic compounds. However, the main focus of the review is to discuss the enormous amount of exciting research on fluorinated liquid crystals that has been reported. The small size of the fluoro substituent enables its incorporation into all types of liquid crystal, including calamitic, discotic, banana, lyotropic, and polymers, without ruining the liquid crystalline nature of the material. However the fluoro substituent is larger than hydrogen, and hence causes a significant steric effect, which combined with the high polarity, confers many fascinating, and often remarkable, modifications to melting point, mesophase morphology and transition temperatures, and the many other very important physical properties, such as dielectric anisotropy, optical anisotropy, and visco-elastic properties. There are many different positions within a liquid crystal structure where a fluoro substituent can be located, including (i) a terminal position, (ii) within a terminal chain, as a semi-fluorinated or as a perfluorinated chain, or as one fluoro substituent at a chiral centre, (iii) as part of a linking group, and (iv) a lateral position in the core section. Such variety enables the interesting and advantageous tailoring of properties, both for the fundamental purposes of establishing structure–property relationships, and for materials targeted towards commercially-successful liquid crystal display applications.

Fluorinated liquid crystals – properties and applications

Discotic Liquid Crystals.

To realise the miniaturised devices, the precise measurement of nanoscale tunnelling current in ultrathin films is of utmost importance. For the nanoscale current measurements, current sensing atomic force microscope (CSAFM) is one of the most powerful tool. CSAFM allows to map the current distribution on the film surface and it permits to perform current measurements as a function of applied bias voltage. It has turned out to be crucial for studies of organic films. In CSAFM, a physical contact is made on film with a precise control of the applied force in nanonewton (nN) range. For the preparation of ultrathin film, Langmuir-Blodgett (LB) technique is known to provide a uniform film with a good control over the thickness in the molecular level. In the last two decades, there have been many CSAFM studies for the tunnelling current measurements. This review is intended to cover the literature on the tunnelling current measurements using CSAFM. Material Science Research India www.materialsciencejournal.org ISSN: 0973-3469, Vol.17, No.(1) 2020, Pg. 62-69 CONTACT Arup Sarkar arupsarkar.katwa@gmail.com Department of Physics, Indian Institute of Science Education & Research, Berhampur 760010, Odisha, India. © 2020 The Author(s). Published by Oriental Scientific Publishing Company This is an Open Access article licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License Doi: http://dx.doi.org/10.13005/msri/170109 Article History Received: 15 March 2020 Accepted: 10 April 2020

Tunnelling Current Measurements Using Current Sensing Atomic Force Microscope

Phosphors the ceramic materials should able to work in tough environment surrounded and bombarded by high energy Vacuum Ultra Violet (VUV), UV or electron beam radiations in any discharge tube. The plasma display panel (PDP) is increasingly gaining attention over conventional cathode ray tube (CRT)- based TVs as a medium of large format (60+”) television (TV), particularly high definition TVs (HDTVs). Improvements have been made not only in size but also in other areas such as resolution, luminescence efficiency, brightness, contrast ratio, power consumption, and cost reduction. The formation of a phosphor host and doping process by solid solution is critical and is highly dependent on the reaction temperature and conditions. Since the purity of starting chemicals is very important to the synthesis of phosphors, the starting chemicals are typically 99.9%, 99.999% in purity. Required amounts of starting ingredients are mixed in the presence of an appropriate flux (if necessary) and fired at high temperatures (1200 °C) in air or in a controlled atmosphere (N 2 , C, CO, or N 2 with 2-5% of H 2 ). The present paper reports the synthesis and luminescence characteristics of different ceramic materials (phosphors) for display applications.

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Ceramic Materials (Phosphors) for Display Applications

Viscoelastic properties of liquid crystals are very important for applications like display technology. However, there are not many direct techniques to study them. In this review, we describe our studies on the viscoelastic modes of some chiral liquid crystals using dynamic light scattering. We discuss viscoelastic modes corresponding to the C director fluctuations in the chiral smectic C phase and the behaviour of the Goldstone-mode near the chiral smectic C-smectic A phase transition. In cholesteric liquid crystals, we consider the director fluctuations in a wavevector range comparable to the inverse pitch of the cholesteric. Here, the study of the scattered light in the vicinity of the Bragg reflection using a novel geometry will be presented.

Viscoelastic modes in chiral liquid crystals

Although viscoelastic properties of liquid crystals are very important for applications like display technology, there are not many direct techniques to study them We have used dynamic light scattering to obtain dispersion curves for the twist mode of director fluctuations in a thermotropic cholesteric liquid crystal (cholesteric) mixture, in a wave vector range comparable to the inverse pitch of the cholesteric In the experiment, light scattered in the vicinity of Bragg reflection is investigated using a hitherto unused scattering geometry where the scattering wave vector q is parallel to the cholesteric helix axis By fitting the experimental data to a parabolic function of the scattering wave vector, we have determined the twist viscoelastic coefficient k
22/γ
1 We have studied the temperature dependence of k
22/γ
1 and found that the viscoelastic coefficient increases rapidly as the cholesteric-to-isotropic transition temperature is approached

K. A. Suresh

Papers

Tunnelling Current Measurements Using Current Sensing Atomic Force Microscope

Ceramic Materials (Phosphors) for Display Applications

Viscoelastic modes in chiral liquid crystals

A dynamic light scattering study of the viscoelastic twist mode in cholesteric liquid crystals

Should entropy always drive a system to disorder