Lateral Fluoro Substituents Research Articles

Synthesis and Characterization of Lateral Fluoro-substituents Liquid Crystals

Lateral difluoro substituent liquid crystal based on a three-aromatic core has been synthesized. It has been designed to correlate the molecular structure and mesomorphism with reference to the difluoro substituent and -COO- linkage group. This compound was characterized by elementary analyses and spectroscopic techniques such as FTIR and 1H-NMR. The synthesis compound's mesomorphic behavior was studied by polarizing optical microscope, differential scanning calorimetry, and dielectric measurements. The recent investigation reveals only SmB phase.

Properties and structural coloured film preparation of some chiral dopants derived from D-Isosorbide

A series of chiral dopants derived from D-isosorbide were synthesized. Some of them exhibita monotropicsmecticA phase. Comparison of the melting points of these chiral dopants, the decrease of them is mainly driven by the large entropy change. The helical twisting power (HTP) values of these chiral dopants with branched alkyl chains, lateral fluoro-substituents and double bonds are lower than those of the chiral dopants with hexyloxy chains. Structural colored polymer films with a right-handed helix are prepared using these chiral dopants.

Benzoxazole-terminated liquid crystals with high birefringence and large dielectric anisotropy

ABSTRACT Six benzoxazole-terminated mesogenic compounds with fluoro substituent at different positions were prepared and their properties investigated. The compounds give a high birefringence (Δn~ 0.45) and a large-dielectric anisotropy (Δε~ 26), indicating a possible application in liquid-crystal mixture as a dopant to enhance performance of the host mixture. In accordance with conventional high Δn liquid crystals containing triple carbon-carbon bonds, lateral fluoro substituents and terminal groups can alter the Δn and Δε of benzoxazole-terminated liquid crystals. Meanwhile, some parameters such as dipole moment, polarisability, dihedral angles are calculated with density functional theory (DFT) methods to relate to the experimental Δn and Δε. It is noted that the introduction of the benzoxazole unit is an effective method to enhance Δn and Δε values of the rodlike molecule, this is ascribed to its π-conjugated benzene-fused heterocycle and large dipole moment.

Synthesis and study the liquid crystalline properties of compounds containing benzoxazole core and terminal vinyl group

ABSTRACTTerminal vinyl-based benzoxazole liquid crystalline compounds, 2-(3-fluoro-4ʹ-alkoxy-1,1ʹ-biphenyl −4-yl)-5-(2-propenyloxymethyl)-benzoxazole (nPPF(2)BP), were synthesised and their structures were confirmed by infrared (IR) spectra, proton nuclear magnetic resonance (1H-NMR) spectra, gas chromatography with electron impact-mass spectrometry (GC/EI-MS), matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry and elemental analysis (EA). The compounds show enantiotropic smectic/nematic phases with mesophase ranges are 71–97 °C and 87–136°C on heating and cooling processes for nPPF(2)BP, respectively. They give low melting points due to lateral fluoro substituent and flexible terminal 2-propenyloxymethyl chain. It is found that the compounds nPPF(2)BP with shorter alkoxy chain (n = 3, 4) exhibit a wide range of nematic mesophase, which is ascribed to enhanced π–π interaction caused by terminal vinyl moiety, whereas further elongation of the terminal alkoxy chain results in supressing nematic phase and increasing smectic mesophase. Compared with methyl terminated analogues, 2-propenyloxymethyl terminated compounds nPPF(2)BP display much lower melting points and wider or comparable mesophase range both in heating and cooling.

Effect of position of the lateral fluoro substituent on the mesophase behaviour of aryl 4-alkoxyphenylazo benzoates in pure and binary mixtures

ABSTRACTFive groups of 4-substituted phenyl 4ʹ-(2ʺ- (or 3″-) substituted-4ʺ-alkoxyphenylazo) benzoates (Ina-c to Vna-c) were investigated in which, within each group, the length of the terminal alkoxy group varies between 8 and 16 carbons, while the other terminal substituent, X, is a polar group that alternatively changed between the electron-donating CH3O and the electron-withdrawing Br group, in addition to the un-substituted analogue (X = H). The lateral substituent (Y) in the five groups I–V varies, respectively, between H, 3-CH3, 2-CH3, 3-F and 2-F. Their mesophase stabilities were determined by differential scanning calorimetry and phases identified by polarised light microscopy. The two newly prepared groups of compounds (IVna-c and Vna-c) are structurally characterised by infrared, 1H-NMR, mass spectroscopy, thermogravimetric and elemental analyses. Binary phase diagrams were constructed for each pair of isomers from groups IV and V bearing the same wing substituents but the lateral F is attached to different positions (2ʺ or 3″).

Investigation of terminal olefine in the isothiocyanatotolane liquid crystals with alkoxy end group

ABSTRACTThree series of liquid crystals based on isothiocyanatotolane core with terminal alkenoxy groups (4A-1‒4C-2) have been synthesised via multi-step reactions. Their thermotropic mesophases and physical properties are evaluated by comparison with the alkoxyl analogues (4a-1‒4c-2). The results show that the isothiocyanatotolane LCs with alkenoxyl terminals deliver higher birefringence (0.410~0.436), lower melting points, lower melting enthalpies and viscosity. The effects of the alkenoxy terminal groups and the lateral fluoro substituents on the mesomorphic behaviour and physical properties are discussed. The formulation of the mixture containing isothiocyanatotolane liquid crystals with alkenoxyl terminals provides evidence of an useful candidate for liquid crystal photonics.

Synthesis and mesomorphic properties of calamitic shaped molecules with chalconyl-ester and lateral fluoro substituents

GRAPHICAL ABSTRACT

Synthesis and properties of allyloxy-based tolane liquid crystals with high negative dielectric anisotropy

ABSTRACTA series of tolane liquid crystals (LCs) containing 2,3-difluorophenyl and allyloxy terminal groups have been synthesised via multi-step reactions. Their thermotropic mesophases, birefringences and dielectric anisotropy properties are discussed by comparison with the non-fluorinated analog. The results show that the allyloxy-based tolane LC 3TOV reveals a high value of the birefringence (0.29), negative dielectric anisotropy (−4.44) and a broad nematic mesophase with a low melting point and high clearing point. The effects of the terminal alkyl chains, the lateral fluoro substituents, the allyloxy terminal group and alkyne bridge on the mesomorphic and physical properties were also discussed. Meanwhile, Density Functional Theory (DFT) calculations of molecular conformation and polarisability were used to correlate the experimental findings.

Synthesis and mesomorphic properties of novel high birefringence azobenzene liquid crystals with lateral fluorosubstituent

ABSTRACTIn order to obtain liquid crystals with high birefringence (Δn), four azobenzene compounds based on lateral fluorinated bistolane moieties with trifluoromethyl terminal groups were synthesized with Hagihara–Sonogashira cross-coupling reaction. The molecular structures of the compounds were confirmed by Fourier transform infrared, 1H-nuclear magnetic resonance. The transition temperatures, optical textures, and optical anisotropies were determined by differential scanning calorimetry, polarizing optical microscopy. The effect of the alkyl substituents on liquid crystal behavior is discussed in detail. The compounds have showed higher birefringence values.

Preparation and characterisation of laterally monofluorinated mesogenic benzimidazole-based compounds

ABSTRACTSeries of laterally monofluorinated compounds, 2-(4ʹ-alkoxy-3-fluorobiphenyl-4-yl)-1H-benzimidazole derivatives (nPPF(3)Mx) bearing different substituents (H, CH3, NO2, coded as nPPF(3)MH, nPPF(3)MM and nPPF(3)MN, respectively) at 5-position, were prepared and their structures were characterised. According to the results from differential scanning calorimetry and polarising optical microscopy, the present compounds nPPF(3)Mx exhibit enantiotropic smectic mesophases, for which the mesophase ranges are 13–67 and 47–111°C on heating and cooling for nPPF(3)MH, 84–112 and 126–154°C for nPPF(3)MM, and 23–102 and 49–117°C for nPPF(3)MN, respectively. Compared to non-fluorinated analogues, monofluorinated nPPF(3)Mx have low melting/clearing points and display enhanced mesophase range both in heating and cooling, which are attributed to the disruption of the side-to-side intermolecular packing caused by the ortho lateral fluoro substituents and the increased dipole–dipole interaction between the polar fluoro-substituted molecules, respectively. It is noted that nPPF(3)MM and nPPF(3)MN show a much wider mesophase range than nPPF(3)MH, which suggest that the substituent at benzimidazole moiety can improve the mesophase stability.

Synthesis and physical properties of tolane liquid crystals containing 2,3-difluorophenylene and terminated by a tetrahydropyran moiety

ABSTRACTFour series of tolane liquid crystals containing 2,3-difluorophenylene and terminated by a tetrahydropyran (THP) moiety have been synthesised via multistep reactions based on 4-alkylcyclohexanecarboxylic acids and 4-bromo-2,3-difluorophenol. Their properties were measured by differential scanning calorimetry, polarising optical microscopy, Abbe refractometer and an electrical constants instrument. The results show that the THP-based liquid crystals nT reveal a relatively high value of the birefringence, negative dielectric anisotropy, good solubility and a broad nematic mesophase. The effects of the terminal alkyl chain, the lateral fluoro substituents and the THP terminal group on the mesomorphic and physical properties are discussed. Meanwhile, density functional theory calculations of molecular conformation and polarisability were conducted to correlate the experimental findings.

Mesophase behaviour of laterally di-fluoro-substituted four-ring compounds

Four new groups of the di-fluoro-substituted 4-(2′-(or 3′)-fluoro phenylazo)-2-(or 3-) fluoro phenyl-4″-alkoxyphenylazo benzoates (In–IVn) were prepared and investigated for their mesophase behaviour. An alkoxy group of variable chain length (n = 6, 10 and 14 carbons) is attached to the terminal phenylazo benzoate moiety, and two lateral fluoro substituents are attached individually with different orientations to the other two adjacent rings. The molecular structures of the prepared compounds were confirmed by Fourier transform infrared spectroscopy and 1H NMR spectroscopy. The study aims to investigate the steric effect of the spatial orientation and relative positions of the two lateral fluorine atoms on the mesomorphic properties in their pure states. The mesophase behaviour was investigated via differential scanning calorimetry and mesophases were identified by polarised light microscopy. The investigation shows that these compounds exhibit high enantiotropic mesophases (SmC and N) and broad mesophase temperature range. The type and stability of the mesophase depends on the length of the terminal alkoxy chain and the position the two fluoro substituents. A comparison between these investigated compounds with their corresponding three-ring analogues was discussed.

Synthesis and the effect of 2,3-difluoro substitution on the properties of diarylacetylene terminated by an allyloxy group

A series of 2,3-difluoro tolane allyloxy-based liquid crystals (LCs), which are composed of the tolane unit, lateral fluoro substituents, alkoxy and allyloxy terminal groups, were synthesised with 4-bromo-2,3-difluorophenol as the starting material via a five-step reaction. Their structures were confirmed by infrared spectroscopy (IR), mass spectroscopy (MS) and nuclear magnetic resonance (NMR). The mesomorphic properties were investigated by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). The dielectric measurement was performed using an independent analyser EC-1 and the birefringence was determined using an Abbe refractometer. The results reveal that LCs have large negative dielectric anisotropy and high birefringence, which are potentially important for the fast response displays and liquid crystal photonic devices (LCDs).

Synthesis, mesomorphic behaviour and optical anisotropy of some novel liquid crystals with lateral and terminal fluoro substituents and a 2,6-disubstituted naphthalene core

The synthesis, mesomorphic properties and optical anisotropy of a range of diphenylnaphthalenes are detailed. One phenyl ring contains two lateral ortho fluoro substituents, with either a terminal butoxy chain or a pentyl chain; in both cases, the other phenyl ring possesses one, two or three fluoro substituents at the end of the molecule. The synthesis of the materials was effected efficiently using a combination of low-temperature lithiations and Suzuki palladium-catalysed cross-coupling reactions. All six novel compounds exhibit the nematic phase at very high temperature (between 125°C and 245°C), particularly those with fewer lateral fluoro substituents, and all show a smectic A phase. The melting points are rather high, but those compounds with a terminal pentyl chain and more lateral fluoro substituents do have much lower melting points (around 100°C). As expected from naphthalene liquid crystals, the optical anisotropy (measured as extrapolated values at 25°C) is very high (0.27–0.35), particularly for those compounds with a terminal butoxy chain and fewer lateral fluoro substituents.

Synthesis and characterisation of benzoxazole-based liquid crystals possessing 3,5-difluorophenyl unit

Series of fluorinated compounds, 2-(3′,5′-difluoro-4′-alkoxybiphenyl-4-yl)-benzoxazole derivatives (nFBx), were prepared and characterised. Their phase transition behaviour was investigated by differential scanning calorimetry and polarising optical microscopy. In the case of carbon atoms in the alkoxy chain between 4 and 10, they exhibited enantiotropic mesophases with the mesophase ranges of 12–119°C and 23–152°C on heating and cooling for compounds bearing different substituents (H, CH3, Cl, and NO2). With the exception of nitro-substituted compounds, the nFBx series displayed intense photoluminescence emission at 380–385 nm in methylene chloride solution when they were excited at their absorption maxima. Compared to non-fluorinated analogues, fluorinated compounds nFBx (apart from nitro-substituted compounds) exhibited much lower melting points, but comparable or slightly narrower mesophase ranges during both heating and cooling, which were attributed to the disruption of the side-to-side intermolecular packing caused by the two lateral fluoro substituents.

Synthesis of fluorinated terphenyl liquid crystals with 3-propylcyclopentane end group

High performance liquid crystal (LC) displays require nematic mixtures with low rotational viscosity to reduce the response time and large dielectric anisotropy to reduce the threshold voltage. Furthermore, liquid crystals (LCs) with low melting temperature and high clearing temperature are particularly attractive for automobile and outdoor display applications. In this article, we report a series of new fluorinated terphenyl LCs with 3-alkylcyclopentane end group. The terphenyl mesogen is designed for high Δn value, and the lateral fluorine atom is used to reduce the melting temperature. In comparison with the terphenyl analogue containing a 4-alkylcyclohexyl end group, discussed in previous works, the obtained LCs show wider nematic temperature range and smaller rotational viscosity because 3-alkylcyclopentyl moiety is introduced. The effect of alkyl chain length and the lateral fluoro substituent on the mesomorphic properties of the obtained LC is discussed. The results show that the nematic temperature range increases with the alkyl chain length increase. The position of the lateral fluoro substituent also plays an important role; LC with the fluoro substitution on the central benzene ring provides the widest nematic temperature range. In conclusion, we have synthesised a new series of LCs with low melting point, wider nematic temperature range and high Δn value, which is promising in formulating eutectic mixture for display application.

Effect of lateral fluoro substituents of rodlike tolanecyano mesogens on blue phase temperature ranges

Several kinds of tolane cyano derivatives with different lateral fluoro substituents are doped with chiral additives to induce the blue phase (BP). Fluoro substituents are found to exert a great effect on the BP ranges for biphenyl mesogens. The laterally difluorinated compounds exhibit wider BP ranges than their corresponding mono-fluorinated homologues when equal chiral dopant is added, while the non-fluorinated compounds show direct isotropic (Iso) to chiral nematic (N*) transitions, even in highly chiral systems. By adjusting the concentrations of the chiral dopant ISO(6OBA)2 in the fluorinated liquid crystals, the BP ranges can be broadened to more than 12 °C. Competition between the steric repulsions caused by the lateral fluoro substituents and π–π interactions of the aromatic cores is supposed to be the main factor that leads to the above results. Apart from this, a weak C–H⋯F interaction may have also been conducive to the BP stabilization.

Novel high birefringence bistolane liquid crystals with lateral fluorosubstituent

Twelve compounds based on lateral fluorinated bistolane moieties with cyano or trifluoromethyl terminal groups were synthesised with Hagihara–Sonogashira cross-coupling reaction. The molecular structures of the compounds were confirmed by Fourier transform infrared, 1H-nuclear magnetic resonance and mass spectrometry. The transition temperatures, optical textures and optical anisotropies were determined by differential scanning calorimetry, polarizing optical microscopy and ultraviolet microscopy. The effects of the terminal substituents and lateral fluorosubstituent group on their physical properties were investigated and discussed. The compounds with lateral double fluorosubstituent and cyano terminal group exhibited nematogenic texture, while other compounds showed smectic phase. All the compounds exhibited wide liquid crystal temperature ranges and high clearing points. Interestingly, the compounds have the high birefringence in the range of between 0.480 and 0.633.

Synthesis of 4-Alkyl-2′′, 3′′ difluoro terphenyl nitrile using coupling reactions

Study of chirality in liquid crystals is one of the most interesting areas of liquid crystal science. Liquid crystalline terphenyls with two lateral fluoro substituent and alkyl substituent in the 4- have been synthesised. Convergent approach was applied which involved the use of arylboronic acids and aryl halides in palladium-catalysed cross-coupling reactions. All the diifluoroterphenyls generate the smectic C phase. Mixture of 4-Alkyl-2′′, 3difluoro terphenyl nitrile in achiral host mixture HM1 generates ferroelectric liquid crystal properties. Ferroelectric properties were found to be highly dependent upon the relative lengths of the alkyl chain attached to chiral dopant. The compounds were studied using optical polarisation microscopy, differential scanning calorimetric, nuclear magnetic resonance, and Instec elecro-optical device to find ferroelectric liquid crystal properties.

Synthesis and properties of allyloxy-based biphenyl liquid crystals with multiple lateral fluoro substituents

Allyloxy-based biphenyl liquid crystals, composed of alkyl chain, trans-cyclohexane and biphenyl mesogenic cores, ethylene linking groups, lateral fluoro substituents and allyloxy terminal groups were prepared via a six-step reaction based on 4-alkylcyclohexanecarbonitrile. Their structures were confirmed via infrared spectrometry, mass spectra and nuclear magnetic resonance. The mesomorphic properties of the present compounds were investigated by differential scanning calorimetry and polarising optical microscopy. The compounds exhibited negative dielectric anisotropy from −3.36 to −4.29 and a broad nematic mesophase with low melting points and high clearing points. The effects of the allyloxy terminal group and the lateral fluoro substituents on the mesomorphic properties and negative dielectric anisotropies are discussed. The present allyloxy-based biphenyl liquid crystals have potential for use in liquid crystal display mixtures.