Search results for " liquid crystal"

Superfluorinated ionic liquid crystals based on supramolecular, halogen-bonded anions

2016

Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen-bonded supramolecular anions [CnF2 n+1-I⋯I⋯I-CnF2 n+1]- are reported. The material system is unique in many ways, demonstrating for the first time 1) ionic, halogen-bonded liquid crystals, and 2) imidazolium-based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation. Out of the ordinary: The high directionality of halogen bonds and the fluorophobic effect were exploited in the design and synthesis of a new family of unconventional superfluorinated ionic liquid crystals. The liquid crystallinity of the system is driven by halogen-bonded…

Ionic liquid crystals based on viologen dimers: tuning the mesomorphism by varying the conformational freedom of the ionic layer

2016

ABSTRACTWe investigated the liquid crystal behaviour of newly synthesised bistriflimide salts of symmetric viologen dimers. A smectic A phase was observed for intermediate spacer lengths and for relatively long lateral alkyl chains. The systems were characterised by thermal analysis, polarised optical microscopy, X-ray scattering and solid-state NMR. An intermediate ordered smectic phase was also exhibited by the compounds (except for systems with very short lateral chains) consisting of molten layers of alkyl chains and partially ordered ionic layers. These results, relating to the mesomorphic behaviour of viologen salts, are qualitatively compared to those of the more common imidazolium s…

Tristriazolotriazines with Azobenzene Arms ‐ Acidochromic Dyes and Discotic Liquid Crystals

2019

Synthesis, Thermal, and Optical Properties of Tris(5‐aryl‐1,3,4‐oxadiazol‐2‐yl)‐1,3,5‐triazines, New Star‐Shaped Fluorescent Discotic Liquid Crystals

2019

Abstract The synthesis of tris(aryloxadiazolyl)triazines (TOTs), C 3‐symmetrical star‐shaped mesogenes with a 1,3,5‐triazine center, 5‐phenyl‐1,3,4‐oxadiazole arms, and various peripheral alkoxy side chains is reported. Threefold Huisgen reaction on a central triazine tricarboxylic acid and suitable aryltetrazoles yields the title compounds. Selected analogues with a benzene center are included in this study and allow for an evaluation of the impact of the central unit on the physical properties. Thermal (differential scanning calorimetry, DSC; polarization optical microscopy, POM), optical (UV/Vis, fluorescence), electric (time of flight, TOF), and structural (single crystal; wide‐angle X‐…

Hexagonal-columnar mesophases of acylated azacrowns with enhanced stabilities

1992

A series of discotic liquid crystals based on completely acylated macrocyclic oligoamines (azacrowns) has been synthesized. Discotic mesophases could be very highly stabilized by making use of an increased steric hindrance, caused by supplemental lateral meta-substituents which were introduced into the cinnamic acids used as the acylation agents. Employing this method yields compounds exhibiting hexagonal mesophases over a very broad range of more than 300°. Even if very large macrocycles are used as the core of such disc-shaped compounds, enantiotropic mesophases are achieved. Themeta-substituents as well as the size of the azacrowns were varied and their influence on the mesomorphic behav…

Discotic Twin and Triple Molecules with Charge-Transfer Interactions in Langmuir−Blodgett Films

1996

X-ray and atomic force microscopy observations reveal features of the surface morphology of Langmuir-Blodgett (LB) films from discotic donor-acceptor molecules with strong core-to-core interactions caused by a charge-transfer (CT) complexation. The compounds are designed to be twin and triple molecules composed of chemically connected donor (triphenylene) and acceptor (trinitrofluorenone) fragments which display liquid crystalline structure in the bulk state. The LB films from these compounds possess edge-on orientation of molecules within monolayers with a smooth surface on a submicron scale but with substantial macroscopic imperfections. These imperfections are represented by the micron s…

Tristriazolotriazines: Luminescent Discotic Liquid Crystals

2018

Synthesis and Characterization of Fluorescent, Low-Symmetry Triphenylene Discotic Liquid Crystals:  Tailoring of Mesomorphic and Optical Properties

1996

A series of monofunctionalized triphenylene-based discotic liquid crystals were synthesized starting from 2-hydroxy-3,6,7,10,11-pentakis(pentyloxy)triphenylene. These compounds are unique in that they possess a single electron-withdrawing group (and consequently a large dipole moment) connected directly to the polyaromatic core. All of the new liquid crystals show a significantly broader range of mesogenicity relative to the parent compound 2,3,6,7,10,11-hexakis(pentyloxy)triphenylene. Moreover, some of the new mesogens exhibit a more ordered mesophase relative to the hexagonal columnar phase (Dh) at lower temperatures. Monofunctionalization of the triphenylene core has a dramatic effect on…

Naturally occurring polyphenols as building blocks for supramolecular liquid crystals – substitution pattern dominates mesomorphism

2021

A modular supramolecular approach towards hydrogen-bonded liquid crystalline assemblies based on naturally occurring polyphenols is reported. The combination of experimental observations, crystallographic studies and semi-empirical analyses of the assemblies provides insight into the structure–property relationships of these materials. Here a direct correlation of the number of donor OH-groups as well as their orientation with the mesomorphic behavior is reported. We discovered that the number and orientation of the OH-groups have a stronger influence on the mesomorphic behavior of the supramolecular assemblies than the connectivity (e.g. stilbenoid or chalconoid) of the hydrogen bond donor…

Photoconductivity in Discotic Liquid Crystals: A New Class of High-Mobility Materials

1994

Abstract Using a time-of-flight technique, different transport mechanisms, deep trapping, multiple shallow trapping and Gaussian transport, can be observed in the different temperature and phase regions of the liquidcrystalline (LC) photoconductor hexapentyloxytriphenylene (HPT). Transient photocurrents and carrier mobilities for various temperatures, electric fields, and sample histories were examined. The ideal intrinsic Gaussian transport, observed for holes in the mesophase, puts HPT into a new class of highmobility materials with both hole mobilities on the order of 1.10−3cm2/Vs and a steplike current decay. These features result from the fact that there is obviously neither a position…