New calamitic thermotropic liquid crystals of 2-hydroxypyridine ester mesogenic core: mesophase behaviour and DFT calculations

ABSTRACT

New three groups of 2-hydroxypyridine ester-based liquid crystals named, 5-[2-(4-substitutedphenyl)diazenyl]pyridin-2-yl 4?-alkoxybenzoate were synthesised. Each group differs from each other by the terminal polar substituent X (CH₃O, Cl and H) which contains five compounds with different numbers (n) of carbons in the alkoxy chain. Mesophase behaviour was investigated for the prepared homologues by differential scanning calorimetry and polarised light microscopy. Elemental analyses, FTIR and ¹HNMR spectroscopy were used for structure confirmation of the prepared compounds. Density functional theory (DFT) theoretical calculations are estimated to prove the experimental data. Stability ranges and the type of the mesophases observed for the investigated compounds were found to be mainly dependent on the length of the alkoxy chain, the polarity, as well as dipole moment and charge distribution. Moreover, the high terminal charge distribution in the case of the methoxy derivative could effect the end-to-end interactions resulting in a nematic phase rather than the ordered Smectic A phase observed in the case of Cl derivatives and the unsubstituted homologues which are non-mesomorphic. Results of the DFT discussed are found to be consistent with the present experimental investigations.     

Bis-Thiourea Bearing Aryl and Amino Acids Side Chains and Their Antibacterial Activities

Abstract

A series of symmetrical 1,3-bis thiourea 1a–e and 1,4-bis thiourea derivatives 2a–e have been successfully synthesized from the reactions of amines with 3-acetylbenzoyl isothiocyanate and 4-acetylbenzoyl isothiocyanate, respectively. All the synthesized compounds were characterized by FT-IR spectroscopy and ¹H and ¹³C NMR spectroscopy. The compounds were screened for their antibacterial activity by turbidimetric method using gram-negative bacteria (E. coli ATCC 8739) using turbidimetric method. The newly synthesized bis-thiourea derivatives bearing aryl side chains showed good antibacterial activity against E. coli. The effect of the molecular structure of the synthesized compounds on the antibacterial activity is discussed.     

Synthesis and mesomorphic properties of 7-alkoxybezopyrano[2,3-c]pyrazol-3-one

A new series of fused polyheterocyclic aromatic compounds, 7-alkoxybezopyrano[2,3-c]pyrazol-3-one (C- n BPP), were synthesised and characterised by infrared, ¹H-nuclear magnetic resonance (NMR), ¹³C-NMR and two-dimensional ¹H-¹³C cosy spectra. Their phase transition behaviour was investigated by differential scanning calorimetry and polarising optical microscopy. All of these compounds showed enantiotropic mesophases with temperature domains of 12–60°C and 22–69°C on heating and cooling processes for a carbon number of the alkoxy chain from 2 to 10. The effect of the length of the alkoxy chain on the mesomorphic properties was discussed. Comparison of C- n BPP and several kinds of coumarin derivatives indicated that the intermolecular hydrogen bonding acted as the driving force of the mesophase formation.     

Schiff base/ester liquid crystals with different lateral substituents: mesophase behaviour and DFT calculations

Four new groups of 4-((2?-substitutedphenylimino)methyl)phenyl-4”-alkoxy benzoates, In_a-d, of Schiff base ester liquid crystals, were prepared and investigated for their mesophase formation and stability. Each group constitutes four homologous series that differ from each other by the lateral attached polar group X in the ortho position for the imine mesogen at terminal benzene ring that alternatively changed from F, Br, NO2 and lateral benzene ring. Within each homologous series, the number (n) of carbons in the alkoxy chain varies between 6, 8, 10 and 12. Molecular structures of the prepared compounds were confirmed via elemental analysis, FT-IR, and ¹H NMR spectroscopy. Mesomorphic properties were investigated by differential scanning calorimetry (DSC) and the phase identified by polarised light microscopy (PLM). A comparative study was made between the investigated compounds and their previously prepared laterally neat, 4-((4?-phenylimino)methyl)phenyl-4”-alkoxy benzoates (IIn); the result revealed that all lateral substituents not only decrease the melting temperature but also the mesophase stability and shown only nematic phase. Density functional theory (DFT) calculations for new lateral derivatives were discussed.     

The synthesis and liquid crystalline behaviour of alkoxy‐substituted derivatives of 1,4‐bis(phenylethynyl)benzene

Despite the prevalence of organised 1,4‐bis(phenylethynyl)benzene derivatives in molecular electronics, the interest in the photophysics of these systems and the common occurrence of phenylethynyl moeties in molecules that exhibit liquid crystalline phases, the phase behaviour of simple alkoxy‐substituted 1,4‐bis(phenylethynyl)benzene derivatives has not yet been described. Two series of 1,4‐bis(phenylethynyl)benzene derivatives, i.e. 1‐[(4′‐alkoxy)phenylethynyl]‐4‐(phenylethynyl)benzenes (5a–5f) and methyl 4‐[(4″‐alkoxy)phenylethynyl‐4′‐(phenylethynyl)] benzoates (18a–18f) [alkoxy = n‐C₄H₉ (a), n‐C₆H₁₃ (b), n‐C₉H₁₉ (c), n‐C₁₂H₂₅ (d), n‐C₁₄H₂₉ (e), n‐C₁₆H₃₃ (f)] have been prepared and characterised. Both series have good chemical stability at temperatures up to 210°C, the derivatives featuring the methyl ester head‐group (18a–18f) offering rather higher melting points and generally stabilising a more diverse range of mesophases at higher temperatures than those found for the simpler compounds (5a–5f). Smectic phases are stabilised by the longer alkoxy substituents, whereas for short and intermediate chain lengths of the simpler system (5a–5c) nematic phases dominate. Diffraction analysis was used to identify the SmB_hex phase in (5d–5f) that is stable within a temperature range of approximately 120–140°C. The relationships between the organisation of molecules within these moderate temperature liquid crystalline phases and other self‐organised states (e.g. Langmuir‐Blodgett films) remain to be explored.     

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 properties of (−)-menthol-derived chiral liquid crystals by introducing adipoyloxy spacer between mesogenic core and chiral menthyl

A homologous series of new chiral liquid crystal compounds, M6BnB (n = 2, 4, 6, 8, 10, 12, 14, 16, 18), with varying length of n-alkoxy chains at one end, was formed by covalently linking a chiral (?)-menthyl with biphenyl-benzoate via adipoyloxy spacer group. A combination of analysis methods such as Fourier transform infrared, ¹H NMR spectra, differential scanning calorimetry, polarised optical microscopy and X-ray diffraction was carried out to systematically investigate their phase structures and phase transition behaviours. The length of the flexible terminal alkoxy group has a profound influence on the clearing points (T_iso) and T_iso decrease with the increase of alkoxy chain (n). In addition, increasing the length of the terminal alkoxy group tends to narrow the temperature range of the N* phase and favour the development of chiral smectic C phase.     

Synthesis and characterisation of asymmetrical mesogenic materials based on 2,5-disubstituted-1,3,4-oxadiazole

New mesogenic homologous series bearing 1,3,4-oxadiazole ring with a nitro terminal group, 4-(5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl)phenyl 4-((4-methoxybenzylidene)amino)benzoate (G₁–G₁₁), were synthesised. Their chemical structures are identified by fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (¹H-NMR) and elemental analysis. The liquid crystalline properties of the series G_n and their precursory F_n were screened by differential scanning calorimetry and optical polarising microscopy (OPM). The compounds of the series G_n were screened by thermogravimetric analysis to observe their thermal stability. The target compounds (G_n) in this study, were displayed different liquid crystalline mesophase, the first two homologous (G₁ and G₂) did not show any liquid crystalline behaviour, the homologous (G₃–G₁₀) which have an alkoxy terminal group (n = 3–10) exhibited nematic phase, whilst the last derivative of the series (G₁₁), n = 12, displayed SmA phase. The mesomorphic properties of these derivatives were affected by the presence of the nitro group at the end of the molecules which was classified as a strong polar group. Also, the role of alkoxy terminal chain and the bent heterocyclic ring (1,3,4-oxadiazole) in the liquid crystalline properties of these molecules were debated.     

Mesophase stability of new Schiff base ester liquid crystals with different polar substituents

Four new groups of Schiff base ester liquid crystal compounds, 4-((4?-substituted phenylimino) methyl)phenyl–4″-alkoxybenzoates, In_a–d, were prepared and investigated for their mesophase formation and stability. Each group constitutes four homologous series that differ from each other by the polar substituent X (CH₃O, CH₃, H, and Cl). Within each homologous series, the number (n) of carbons in the alkoxy chain varies between 6, 8, 10, and 12. Molecular structures of the prepared compounds were confirmed via FT-IR, ¹H NMR, mass spectroscopy, and elemental analysis. The mesomorphic properties were investigated by differential scanning calorimetry and polarised light microscopy. Comparative studies between the present series and previously investigated 4-(4-substituted phenylazo)phenyl 4″-alkoxybenzoates revealed that the phenylimino mesogenic core increases the mesophase stability rather than the azo analogues.     

Columnar liquid crystalline benzenetrisamides with pendant 1,3,4-oxadiazole groups

Novel liquid crystal materials based on 1,3,5-benzenetrisamide derivatives with three pendant 2-phenyl-5-(mono-, di-, and/or tri-n-alkoxyphenyl)-1,3,4-oxadiazole arms (Ia–c, IIa–c) were prepared. The mesomorphic properties of these compounds were characterised and studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The formation of a columnar mesophase was found to be dependent on the number of alkoxy side chains. The compounds Ib and IIb, with a total of six alkoxy chains, and compounds Ic and IIc, with nine alkoxy chains, exhibited an enantiotropic hexagonal columnar (Col_h ) phase with high isotropisation temperatures; however, compounds Ia and IIa with a total of three alkoxy chains formed a crystalline phase. Compounds IIb and c were room temperature liquid crystals.     

含亚胺和胆甾烯基不对称液晶二聚体的合成及介晶性

报道含亚胺和胆甾烯基不对称液晶二聚体化合物XC₆H₄N＝CHC₆H₄OC₁₀H₂₀COOCh* [X＝OC_nH_2n＋1, (n＝1～12,14), F, Cl, Br, CH₃] (1a～1q)的合成及液晶性. 目标化合物通过600 MHz ¹H NMR和元素分析进行了结构表征. 其介晶性通过偏光显微镜(POM)和差示扫描量热计(DSC)进行了研究. 结果显示: 所有化合物都具有胆甾相(N*). 对于烷氧基系列(X＝OC_nH_2n＋1), 有部分化合物还呈现了近晶A相(S_A), 且随着末端烷氧链长度的增加, 化合物的清亮点呈现缓慢下降的趋势, 而化合物从胆甾相到各向同性液体转变的熵变(ΔS_N*→I)则呈现奇-偶效应. 同时我们对比研究了取代基X对胆甾相稳定性的影响, 发现取代基X对胆甾相的稳定性高低顺序为: MeO＞Cl＞Br＞Me＞F. 这些结果证实了末端取代基的改变对化合物的相转变温度以及介晶性质有显著的影响.     

Effect of including extra phenylazo moiety on the mesophase behaviour of three-ring azo/ester molecules

Five homologous series of the four-ring 4-substituted phenylazo phenyl 4?-(4?-alkoxy phenylazo) benzoates (In_a–e) were prepared and their mesophase behaviour investigated by differential scanning calorimetry (DSC) and phases identified by polarised light microscopy (PLM). Compounds prepared were structurally characterised via infrared, ¹H-NMR, mass spectroscopy, thermogravimetric and elemental analysis. Transition temperatures were first correlated with the alkoxy-chain length (n, that varies between 6, 8, 10, 14, and 16 carbons) within each homologous series, and again with the polarisability anisotropy (Δα_X) of the Ar-X bond, where X changes between CH₃O, CH₃, H, Br, and CN groups . Comparative studies were made to investigate the effect of introducing the extra phenyl azo moiety into the previously investigated three-ring compounds, 4-substituted phenyl 4′-(4″-alkoxyphenylazo) benzoates (IIn_a–e), 4-substituted phenylazo 4′-(4″- alkoxy phenyl) benzoates (IIIn_a–e), and 4-(4′-alkoxy phenylazo) phenyl 4″-substituted benzoates (IVn_a–e), each bear the same polar group, X, and the alkoxy group, n .     

Mononuclear copper(I) complexes with triphenylphosphine and N,N′-disubstituted thioureas: synthesis,characterization, and biological evaluation

Abstract

Twelve new complexes, of the general formula CuCl(TPP)₂Tu^1–12 (Tu?=?thiourea), were synthesized by the reaction of CuCl(TPP)₃ (TPP?=?triphenylphosphine) and various N,N′-disubstituted thioureas. The structures of the synthesized complexes were characterized by different techniques such as Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy (¹H, ¹³C, ³¹P, and ¹⁹F), and the representative complexes (1, 2 and 12) were analyzed via single crystal X-ray diffraction. The single crystal X-ray analysis revealed that copper(I) is coordinated with chlorine, two TPP, and the thiourea ligands through the sulfur atom in a mononuclear distorted tetrahedral mode. The compounds were tested for antibacterial, antifungal, cytotoxicity, antileishmanial, and antioxidant activities. The results showed that the synthesized complexes are significantly more active than the free ligands and the commercial reference compounds. The high biological activities of the complexes versus free ligands can be attributed to the copper(I) chloride complexation with thiourea ligands. The synthesized complexes were also evaluated, both experimentally and theoretically, for DNA binding studies. The UV-visible spectroscopic and molecular docking studies demonstrated that the complexes are conjugating with DNA through a groove binding mode.     

Phosphinoyl and Thiophosphinoylcarbodithioates: Synthesis,Molecular Structure,and Application as New Efficient Mediators for RAFT Polymerization

New phosphinoyl and thiophosphinoylcarbodithioates were synthesized in a one‐pot reaction from the corresponding phosphinochalcogenides. Compounds of this new generation of thiocarbonylthio derivatives have been fully characterized by IR as well as ¹H, ³¹P, and ¹³C NMR spectroscopy and by mass spectrometry. Their solid‐state structures reveal that they are isostructural but crystallize in different space groups. These new compounds are highly efficient reversible chain‐transfer agents for the reversible addition‐fragmentation chain transfer (RAFT) polymerization of styrene (St) and n‐butyl acrylate (nBA), with controlled number‐average molecular weights (M_n) and narrow dispersity values (Ð<1.3). The controlled character of the polymerization was further exemplified by MALDI‐TOF mass spectrometry and the synthesis of PSt‐P(nBA) diblock copolymers.     

Synthesis,characterization and antimicrobial activities of transition metal complexes of N,N -dialkyl- N′ -(2-chlorobenzoyl)thiourea derivatives

N,N-di-n-propyl-N′-(2-chlorobenzoyl)thiourea (HL¹) (1), N,N-diphenyl-N′-(2-chlorobenzoyl)thiourea (HL²) (2), and their Ni^II, Co^II, Cu^II, Zn^II, Pt^II, Cd^II and Pd^II complexes have been synthesized and characterized. HL¹ and its copper complex were characterized by single-crystal X-ray diffraction methods. The ligands coordinate as bidentates yielding essentially neutral complexes of the type [ML₂]. The complexes were screened for their in vitro antibacterial, antifungal activities and toxicity. All compounds showed antimicrobial activity, but antibacterial efficacy is greater than antifungal activity.     

Influence of lateral methyl and terminal substituents on the mesophase behaviour of four rings azo-ester liquid crystal compounds

ABSTRACT

The effect of introducing a lateral methyl substitution into the previously investigated laterally neat four-ring analogues, 4-substituted phenylazo phenyl 4?-(4?-alkoxyphenylazo) benzoates (In_a–e), on their mesophase behaviour was investigated for the newly prepared five homologous series of 4-substituted phenylazo phenyl 4?-(3?-methyl-4?-alkoxyphenylazo) benzoates (IIn_a–e). Within each homologous series, the alkoxy group varies between 6, 8, 10, 12, 14, and 16 carbons, while the substituent, X, is a polar group that alternatively changes between the electron-donating (CH₃O and CH₃) groups, and the electron-withdrawing (Br and NO₂) groups, including the unsubstituted homologues (IIn_c). Their mesophase stabilities were determined by DSC and phases identified by PLM. The results showed that independent of the alkoxy-chain length or the polarity of the substituent X, the nematic phase is predominant with relatively high stability and wide temperature ranges. All compounds show a good thermal stability in the mesophases domain, except the nitro and Br substituted derivatives bearing short alkoxy chain length. Comparison of the mesophase behaviour was also made between the present series and corresponding three-ring laterally CH_3-substituted azo/ester analogues. UV-vis absorption spectra revealed that derivatives with electron donating or an electron withdrawing groups exhibited redshifts of the π→π* transition compared with unsubstituded derivative.     

Synthesis and mesomorphic properties of 2-(4′-alkoxybiphenyl-4-yl)-1H-benzimidazole derivatives

Three series of 2-(4′-alkoxybiphenyl-4-yl)-1H-benzimidazole derivatives (nM-x), which possessed 5-nitrobenzimidazole (nM-N series), benzimidazole (nM-H series) or 5-methylbenzimidazole (nM-M series) units at the end of the molecule, were synthesised and characterised by infrared, ¹H- and ¹³C-nuclear magnetic resonance spectra, electrospray ionisation-mass spectrometry and elemental analysis. Their phase transition behaviour was investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. All the compounds exhibited enantiotropic smectic mesophases with wide temperature domains for a carbon number in the alkoxy chain from 6 to 16, where the mesophase ranges were 14–91°C and 17–99°C during heating and cooling processes for the nM-N compounds, 7–25°C and 8–49°C for the nM-H compounds and 48–81°C and 52–85°C for the nM-M compounds, respectively. The effect of the length of alkoxy chain on mesomorphic properties was discussed. The nM-N and nM-M exhibited a much wider mesophase range whether during heating or cooling process than the corresponding nM-H series, especially for the longer terminal chain (n > 8), which indicated that the substituent in the benzimidazole moiety was helpful in increasing the mesophase stability.     

Side-Chain Liquid-Crystalline Polymers with Polystyrene Backbone

Abstract

A series of liquid-crystalline polystyrene derivatives with pendant mesogenic groups has been prepared and characterized. The side-chain is connected to the polystyrene backbone by a methyleneoxyhexyloxy spacer. The mesogenic group is a 4-alkoxy substituted biphenyl group. The length of the alkoxy end-group varied from a methoxy group to an octyloxy group. The polymers were synthesized by a radical reaction. Molar masses (M _n) varied between 17,000 and 46,000, with a molar mass distribution between 1.6 and 2.0. All the polymers were liquid-crystalline, with enantiotropic smectic phases. The polymers were characterized with polarizing microscopy, NMR spectroscopy, and calorimetry.     

Synthesis, characterization and thermal behavior of 1,1-dialkyl-3-(4-(3,3-dialkylthioureidocarbonyl)-benzoyl)thiourea and its Cu(II), Ni(II), and Co(II) complexes

We report the synthesis, characterization, and thermal behavior of 1,1-diethyl-3-(4-(3,3-diethylthioureidocarbonyl)benzoyl)thiourea, 1,1-di-n-propyl-3-(4-(3,3-di-n-propylthioureido carbonyl)benzoyl)thiourea and 1,1-di-n-butyl-3-(4-(3,3-di-n-butylthioureidocarbonyl)benzoyl)thiourea and their Ni(II), Cu(II), and Co(II) complexes. The structure of the prepared compounds was determined by elemental analysis, FT-IR, ¹H NMR spectroscopy and mass spectrometry. The ligands are coordinated to metal atoms in a bidentate manner yielding an essentially neutral complex of the type M₃L₃. Thermal decomposition of related compounds was investigated by DTA and TG techniques. The pyrolytic end product was identified by X-ray powder diffraction method. The text was submitted by the authors in English.     

Liquid-Crystalline Properties of Unsaturated Piperazine-2,5-dione Derivatives

The synthesis, characterization, and mesomorphic properties of a new type of liquid-crystalline compounds, (3Z,6Z)-3,6-bis(3,4-dialkoxybenzylidene)piperazine-2,5-diones are reported. These compounds were derived from unsaturated piperazine-2,5-dione as the core group, and were prepared by condensation reactions of 1,4-diacetylpiperazine-2,5-dione and 3,4-dialkoxybenzaldehydes. The products were characterized by ¹H- and ¹³C-NMR spectroscopy, and elemental analysis, and the phase behavior of these compounds was characterized and studied by differential scanning calorimetry (DSC) and polarization microscopy. The results indicate that these rod-like compounds exhibit smectic C (S_c) phases. However, for the derivatives with two flexible alkoxy side chains, highly ordered smectic G (S_G) phases were also formed and confirmed by X-ray powder diffraction. The liquid crystallinity of these molecules was attributed to the presence of intermolecular hydrogen bonds involving the NH groups of the heterocyclic rings. The correlation of phase behavior and molecular shape is also discussed.