Room Temperature Discotic Liquid Research Articles

Temperature-dependent hole mobility in pyrene-thiophene-based room-temperature discotic liquid crystals.

π-Conjugated pyrene-thiophene-based room-temperature discotic liquid crystals armed with four peripheral aliphatic chains are reported to study their potential use in a hole-transporting organic semiconductor. The charge carrier mobility studies using the ToF method revealed room temperature hole mobility in the order of 10-4 cm2 V-1 s-1 for both mesogens. However, the mobility values for compound 1a were observed in the order of 10-3 cm2 V-1 s-1 at high temperatures. Such molecular systems can potentially be used in nonlinear organic electronic applications.

Room-temperature triphenylene-based discotic liquid crystal dimers: effects of amide linkage and central fluoromethylene spacer

ABSTRACT Two series of triphenylene-based dimers both having a central fluoromethylene spacer of four or six carbon atoms and ester or amide linkages were synthesised and their phase behaviour investigated. All the synthesised dimers are room-temperature discotic liquid crystals and exhibit hexagonal columnar mesophases that supercool into a stable anisotropic columnar glass. The length of the fluoromethylene spacer has a minor effect on the phase transition temperatures of these dimers. However, dimers 1a and 2a with a (CF2)4 spacer exhibit approximately 40°C higher clearing points and wider mesomorphic phase ranges compared with their hydrocarbon analogs 1c and 2c with a (CH2)4 spacer respectively. Compared to the corresponding ester-linked dimers 1a-c, three amide-linked dimers 2a-c exhibit 20°C higher clearing points upon cooling. The observation indicates not only that the introduction of the fluoromethylene spacer stabilised the mesophase in these discotic dimers, but also that the two interactions have synergistic effects on columnar packing in this system. Moreover, only amide-linked dimers exhibit good gelation property in a mixture of toluene and petrol ether, with a lower critical gelation concentration of 1.5 wt/vol%, thus indicating that gel formation occurred under the collaboration of hydrogen bonding and intrinsic π interactions in these dimers.

First examples of room-temperature discotic nematic liquid crystals exhibiting ambipolar charge carrier mobilities.

Four new room-temperature nematic liquid-crystalline (LC) dimers consisting of a wedge-shaped 3,4,5-tridecyloxy gallic ester molecule linked to either cyanobiphenyl, cholesteryl, pentaalkynylbenzene or triphenylene based moieties are reported. Dimers with pentaalkynylbenzene and triphenylene moieties in their room-temperature discotic nematic (ND) mesophase show ambipolar charge carrier mobilities of the order of 10-5 cm2 V-1 s-1 and 10-3 cm2 V-1 s-1, respectively, as measured using a time-of-flight (ToF) technique.

Corrigendum/Addendum to “Strengthening of columnar hexagonal phase of a room temperature discotic liquid crystalline material by using ferroelectric barium titanate nanoparticles” [J. Mol. Liq. 294 (2019) 111609

In this Corrigendum/Addendum, we present correction to our published article “Strengthening of columnar hexagonal phase of a room temperature discotic liquid crystalline material by using ferroelectric barium titanate nanoparticles” [J. Mol. Liq. 294 (2019) 111609]. Correction include Table 1: Thermodynamic parameters for RTAQ and composites. The effect of correction on the DSC thermogram is negligible, hence the results and discussion, and the conclusion section remains unchanged. However, for the convenience of readers, we correlate the discussion on the basis of corrected values with the discussion of previously published work.

Magnified charge carrier conduction, permittivity, and mesomorphic properties of columnar structure of a room temperature discotic liquid crystalline material due to the dispersion of low concentration ferroelectric nanoparticles.

Liquid crystal nanocomposites have been a hot topic of research due to optimization of physical properties with such blending. There are several reports on enhancement of physical properties of nematic liquid crystals due to the blending of the nanomaterials. L. M. Lopatina and J. V. Selinger [Phys. Rev. Lett. 102, 197802 (2009)]10.1103/PhysRevLett.102.197802 have even proposed a theory based on experimental results for the enhancement of the properties of the nematic mesophase in the presence of ferroelectric nanoparticles. However, discotic liquid crystal nanocomposites are less studied. In the present experimental work, we have studied the effect of ferroelectric (BaTiO_{3}) nanoparticles on a room temperature discotic liquid crystalline material, namely 1,5-dihydroxy-2,3,6,7-tetrakis(3,7-dimethyloctyloxy)-9,10-anthraquinone. We investigated the physical properties of low concentration ferroelectric nanoparticle dispersed discotic columnar structure, using calorimetric, optical, x-ray diffraction, and dielectric spectroscopy tools. Results show that inclusion of ferroelectric nanoparticles in the discotic matrix consolidates the stability of the columnar matrix of the Col_{h} phase by virtue of their ferroic nature. An enhancement in charge carrier conductivity by several orders of magnitude at ambient conditions has been observed which makes such systems highly appropriate for one-dimensional conductors. Low concentration of BaTiO_{3} nanoparticles substantially enhanced permittivity of the system also. A molecular relaxation mode has been observed in the middle frequency range of the dielectric spectra. Enhancement of these important parameters could be possible due to the ferroelectric nature of the dispersed nanoparticles.

Correction: Room temperature discotic liquid crystalline triphenylene-pentaalkynylbenzene dyads as an emitter in blue OLEDs and their charge transfer complexes with ambipolar charge transport behaviour

Correction for ‘Room temperature discotic liquid crystalline triphenylene-pentaalkynylbenzene dyads as an emitter in blue OLEDs and their charge transfer complexes with ambipolar charge transport behaviour’ by Indu Bala et al., J. Mater. Chem. C, 2019, 7, 5724–5738.

Strengthening of columnar hexagonal phase of a room temperature discotic liquid crystalline material by using ferroelectric barium titanate nanoparticles

A discotic liquid crystalline (DLC) material possessing a wide room temperature columnar hexagonal phase has been used as a polymeric matrix to disperse ferroelectric barium titanate nanoparticles at the concentrations of 0.5 wt% and 1.0 wt% respectively. The influence of nanoparticles on the discotic liquid crystal has been studied with the help of Differential Scanning Calorimetry, impedance spectroscopy, polarizing optical microscopy and Ultraviolet-Visible spectroscopy. Small angle X-ray scattering (SAXS) measurements have also been performed. Thermal measurements reveal stabilization of the columnar hexagonal phase due to the addition of ferroelectric nanoparticles in the discotic system. Permittivity is decreasing due to the formation of anti-dipolar ordering in the presence of ferroelectric nanoparticles. A relaxation mode is visible in the high kHz to low MHz region. The relaxation frequency has been found to decrease with the incarceration of barium titanate nanoparticles in DLC. A shift in UV–Vis absorption/transmittance spectra indicates modification in the electronic structure and hence physical property of the nanocomposites. SAXS explains the variation of different hexagonal lattice parameters with respect to the temperature.

Room temperature discotic liquid crystalline triphenylene-pentaalkynylbenzene dyads as an emitter in blue OLEDs and their charge transfer complexes with ambipolar charge transport behaviour

Room temperature discotic dyads as emitters in blue OLEDs and their TNF complexes with ambipolar charge transport properties.

Supramolecular self-assembly of thiol functionalized pentaalkynylbenzene-decorated gold nanoparticles exhibiting a room temperature discotic nematic liquid crystal phase

First example of a room temperature discotic nematic liquid crystal made of gold nanoparticles.

Heptazine: an Electron-Deficient Fluorescent Core for Discotic Liquid Crystals.

Herein, room-temperature discotic liquid crystals based on heptazine, an electron deficient central core, are reported for the first time. Mesomorphic behaviors of the materials are also investigated. Supramolecular assembly of the mesophase derivatives were confirmed by X-ray scattering experiments. Heptazine-based solid thin films are strong blue light emitters, whereas in the solution state, they are weakly emissive or non-emissive. The band gap energy is found to be low in this class of compounds. Formation of room-temperature mesophases, low band-gap behavior, and strong blue-light emission in the solid state are promising attributes for optoelectronic applications of the materials.

A room-temperature heptazine core discotic liquid crystal

ABSTRACTHeptazine is the fundamental structural and functional unit of graphitic carbon nitrides and has a π-conjugated planar symmetry with semiconducting properties. Molecular self-assembly is one of the key factors to drive the electronic behaviour of π-conjugated organic molecules. To enhance the semiconductivity, heptazine is decorated at its active sites with 2,3,5-tris(dodecyloxy)aniline to get well-organised columnar packing. A novel heptazine-core room-temperature discotic liquid crystal (HDLC) with hexagonal columnar geometry is discovered. The molecular structure and mesomorphic properties of HDLC are investigated by 1H-NMR, 13C-NMR, IR, polarised optical microscopy, differential scanning calorimetry and X-ray diffraction. Photophysical and electrochemical properties of HDLC are studied by UV–vis/fluorescence spectroscopy and cyclic voltammetry (CV), respectively. The energy band gap of HDLC estimated from CV at room temperature is 1.63 eV, which is much narrower than the previously reported band gap for heptazine derivatives. This decrease in the energy band can be attributed to the particular designing of HDLC for columnar packing. As a columnar liquid crystal providing a smooth path to the charge transport, HDLC with such a narrow energy band gap may find applications in organic electronics.

TNF Induced Switching of Columnar Rectangular to Hexagonal Assemblies in a New Class of Triphenylene-Based Room Temperature Discotic Liquid Crystals.

A straightforward synthesis of triphenylene-based oligomeric systems that self-organize into room temperature columnar structures is presented. The compounds with longer spacer length (m = 10 and 12) exhibit columnar rectangular (Colr) mesophase whereas the compound with m = 8 exists in glassy Colr state. Interestingly, the Colr self-assembly of these compounds switches to columnar hexagonal (Colh) on doping the compounds with 2,4,7-trinitrofluorenone (TNF). For the dopant concentration of 1:1 with respect to native compound, an intermediate transition state between Colr and Colh phase was observed which completely transformed into the hexagonal phase on increasing the concentration to 1:2 (compound: TNF) and afterward. Both the Colr and Colh self-assemblies have been well resolved by detailed X-ray analysis. These kind of oligomeric compounds generally possess a combination of desirable alignment properties analogous to monomeric compounds and long-lived glassy states similar to that of polymeric mesogens. In addition, charge hopping behavior is expected to increase in these compounds due to donor-acceptor interactions. Overall, these compounds can find possible potential applications in semiconductor devices.

A new strategy towards the synthesis of a room-temperature discotic nematic liquid crystal employing triphenylene and pentaalkynylbenzene units.

A new approach is reported for the design of a room-temperature discotic nematic (ND) liquid crystal (LC) dimer consisting of a triphenylene and a pentaalkynylbenzene unit linked via flexible alkyl spacers. The formation of the ND phase is realized most likely through folding of the dimeric molecule that prevent stacking between the triphenylene units, as suggested by modelling in the mesophase derived from X-ray scattering results and high-level DFT calculations.

Cover Picture: Unsymmetrically substituted room temperature discotic liquid crystals based on hexa–peri–hexabenzocoronene core (ChemistrySelect 5/2016)

Cover Picture: Unsymmetrically substituted room temperature discotic liquid crystals based on hexa–<i>peri–</i>hexabenzocoronene core (ChemistrySelect 5/2016)

Unsymmetrically substituted room temperature discotic liquid crystals based on hexa–peri–hexabenzocoronene core

AbstractThe first discotic system based‐on alkoxy (tri‐ &amp; di‐) substituted hexa‐peri‐hexabenzocoronene (HBC) that self‐organizes into room temperature columnar structure is reported. Tri‐ and di‐ substituted HBC derivatives showed reddish and yellowish green fluorescence under long wavelength (365 nm) UV light illumination in solution as well as in thin films in the liquid crystalline (LC) state at room temperature, respectively. Thermotropic LC behavior of these compounds was studied by differential scanning calorimetry, polarized optical microscopy and small‐ and wide‐angle X‐ray scattering. Tri‐alkoxy derivative was found to self‐organize into a highly ordered columnar rectangular mesophase, while the other (di‐) possessed a columnar hexagonal mesophase, indicating that in spite of their non‐planarity, the aromatic cores in the mesophase are tightly packed to give highly ordered phases. This system is a promising candidate as an active component of organic light emitting devices, due to its facile processability, low band gap, luminescence and exceptionally higher ordered self‐organization behavior in the mesophase derived from X‐ray scattering studies.

Triphenylene-Based Room-Temperature Discotic Liquid Crystals: A New Class of Blue-Light-Emitting Materials with Long-Range Columnar Self-Assembly.

A straightforward synthesis of multialkynylbenzene-bridged triphenylene-based dyad systems (via flexible alkyl spacers) that self-organize into room-temperature columnar structures over a long range is reported. The compounds with spacer lengths (n) of 8 and 10 exhibit a columnar rectangular mesophase whereas a compound with n = 6 shows a columnar rectangular plastic phase. Interestingly, the later compound (n = 6) shows the formation of well-nucleated spherulites of about several hundred micrometers that suggest the existence of a long-range uniform self-assembly of columns. All of these compounds show blue luminescence in solution and in the thin-film state under long-wavelength (365 nm) UV light. These compounds fulfill the described demands such as long-range columnar self-assembly at room temperature, a good yield with high purity, and blue-light emitters under the neat condition for possible potential applications in semiconductor devices. They also match the criteria of facile processing from the isotropic state because of their low isotropization temperature. This new class of materials is promising, considering the emissive nature and stabilization of the columnar mesophase at ambient temperature.

Unusual temperature dependence of elastic constants of an ambient-temperature discotic nematic liquid crystal.

We report the first experimental studies on the temperature dependence of viscoelastic properties of a room temperature discotic nematic liquid crystal. The splay elastic constant is greater than the bend elastic constant and both show unusual temperature and order parameter dependence. The rotational viscosity is remarkably larger than conventional calamitic liquid crystals. We provide a simple physical explanation based on the columnar short-range order to account for the the unusual temperature dependence of the elastic constants.

Cadmium selenide quantum dots for the amelioration of the properties of a room temperature discotic liquid crystalline material

The effect of cadmium selenide quantum dots on a room temperature discotic liquid crystalline material has been studied.

Single-component room-temperature discotic nematic liquid crystals formed by introducing an attraction-enhancing in-plane protrusion onto the hexa(phenylethynyl)benzene core

Single-component room-temperature discotic nematics have been achieved within large temperature ranges by introducing an attraction-enhancing protrusion onto hexa(phenylethynyl)benzenes. X-ray diffraction investigations revealed the nematic phases of these new discotic nematic materials to be cybotactic.

Anthraquinone-Based Discotic Liquid Crystals

The syntheses of six room-temperature discotic liquid crystals based on an alkoxy-anthraquinone (AQ) framework is described. Differential scanning calorimetry, X-ray diffraction (XRD), and cross-polarized microscopy were used to identify phases and confirm phase-transition temperatures. Cross-polarized microscopy results suggest columnar discotic structures at room temperature. However, the AQ derivatives also undergo mesophase-to-mesophase transitions, which are attributed to rectangular- to hexagonal-columnar discotic transitions based on XRD analysis. Furthermore, some of the compounds display remarkable liquid crystalline phase stability that spans from -50 to 150 degrees C, a useful temperature range for organic materials applications. The different AQ derivatives did not exhibit electronic perturbations, as all compounds have absorption onsets of approximately 400 nm. Finally, solution cyclic voltammetry of the AQ derivatives was carried out to determine the redox potentials, diffusion coefficients, and electron transfer rate constants. All AQ derivatives had E(1/2) values that ranged between -1.52 and -1.70 V vs Fc/Fc(+). Diffusion coefficients and electron transfer rates for all AQ derivatives ranged between 0.4 and 7.1 x 10(-6) cm(2) x s(-1) and 0.9 and 5.2 x 10(-3) cm x s(-1), respectively.