Multi-arm ionic liquid crystals formed by cholesteric mesophase and pyridinium groups

ABSTRACT

A series of novel star-shaped ionic liquid crystals (ILCs) compounds with various counterions (derived from HBF₄, HPF₆, CF₃COOH, d-MH-SO₃H, H₃PO₄, p-Toluenesulfonic acid) were designed and synthesised starting from precursors of pyridines and liquid crystalline monomer cholesteryl 4-bromobutanoate. Inducing various counterions by use of ionic self-assembly due to electrostatic attraction of various ion clusters was one of the most essential factors for intermolecular separation. The chemical structures, liquid crystalline properties, self-assembly behaviour and ionic conductivity of these compounds were researched during multiple experimental techniques. The star-shaped ILCs showed a smectic A (SmA) mesophase. The d-spacing of star-shaped ILCs increased slightly due to the increase volume of anion. The clearing temperatures of the pyridinium salts suggested that the effect of the stabilisation on the SmA structures was in the order H₂PO₄^?>BF₄^?>T_S^?>D-MH-SO₃^?>CF₃COO^?>PF₆^?. All these star-shaped ILCs displayed ionic conductivity in mesophase. It was noted that the conductivity (σ) increased with the increase of the anion size and temperature.     

Polymerised ionic liquid crystals bearing imidazolium and bipyridinium groups

Novel kinds of polymerised ionic liquid crystals (PILCs) bearing imidazolium and bipyridinium groups were synthesised and characterised in this work. Some bromo-polyesters were synthesised in an esterification chain reaction using 2,3-dibromosuccinyl dichloride, isophthaloyl chloride and 4,4′-biphenol. The polyester imidazolium bromides (PIBs) and polyester dipyridinium bromides (PDBs) were obtained by a quaternisation reaction between the bromo-polyesters, N-methylimidazole and 4-4′-bipyridine, respectively. The polyester imidazolium tetrafluoroborates (PITs) and polyester dipyridinium tetrafluoroborates (PDTs) were synthesised using the corresponding PIBs and PDBs in an anion-exchange reaction. The chemical structures, liquid crystalline properties and molecular weights of these polymers were characterised by multiple experimental techniques. All the PILCs including PIBs, PDBs, PITs and PDTs display smectic A phase on heating and cooling cycles. The liquid-crystalline properties of bromo-polyesters are influenced by the length of flexible spacer and composition of polyester backbones, while those of PILCs are determined by the ionic groups as additional important influent factors. In comparison with those of the mother bromo-polyesters, the d-spacing of PILCs reduced slightly due to Im⁺–Br^?, Dp⁺–Br^?, Im⁺–BF₄^? and Dp⁺–BF₄^? ion pairs in the polymer systems. Monocationic imidazolium salts display weaker interionic and intermolecular interaction, higher mobility and lower viscosity than dicationic dipyridinium salts.     

Octahedral copper(II) carboxylate complex: synthesis,structural description,DNA-binding and anti-bacterial studies

Self-assembly of CuSO₄, para-methyl-2-phenyl acetate and 1,10-phenanthroline afforded good-quality crystalline complex in quantitative yield. The complex was characterized by FTIR and UV-visible spectroscopy, electrochemistry, and powder and single-crystal XRD studies. Its structure was found to possess axially elongated octahedral symmetry with CuO₄N₂ chromophore. Its purity was assessed by powder XRD spectrum. Absorption study yielded a broad band corresponding to ²E_g→²T_2 g transition. Electrochemical solution study indicated diffusion-controlled irreversible electron transfer process corresponding to Cu(II)/Cu(I) redox couple with diffusion coefficient = 7.89(±0.1)×10^?9 cm²s^?1. Results of spectroscopic techniques support each other. Complex exhibited excellent DNA-binding ability through UV-visible spectroscopy and cyclic voltammetry yielding K_b values 1.399 × 10⁴ M^?1 and 5.81 × 10³ M^?1, respectively. The complex exhibited significant activity against bacterial strains Escherichia coli, Micrococcus luteus and Staphylococcus aureus and good activity against Bacillus subtilis. These preliminary studies impart good biological relevance on the synthesized complex.     

Thermal properties of sulfonic acid group functionalized Brönsted acidic ionic liquids

Thermal decomposition onset temperatures have been measured for a total of 24 methylimidazolium, triethanolammonium, and pyridinium type sulfonic acid groups functionalized Brönsted acidic ionic liquids with Cl^?, Br^?, SO₄ ^2?, PO₄ ^3?, BF₄ ^? _, CH₃CO₂ ^?, and CH₃SO₃ ^? anions, using thermogravimetric analysis. Thermal stabilities of these sulfonic acid group functionalized ionic liquids decreases in the order, methylimidazolium > triethanolammonium > pyridinium. The methylimidazolium, pyridinium, and triethanolammonium ionic liquids investigated showed decomposition onset temperatures (air) in the 213–353, 167–240, and 230–307 °C ranges, respectively. Additionally, the decomposition temperatures of these ionic liquids are highly dependent on the nature of the anion.     

Synthesis and Chemical Properties of Diacetylenes with Pyridinium and 4,4′‐Bipyridinium Groups

Diacetylenes (DAs) having a dipolar D‐π‐A structure (D=donor: amino group; π=π‐conjugation core; A=acceptor: pyridinium (Py) and bipyridinium (BPy) groups), i.e., 4 (APBPyDA) and 5 (APPyPyDA), or an A‐π‐A structure, i.e., 7 (DBPyDA) and 8 (PyDA(Cl)), were obtained by 1 : 1 and 1 : 2 reactions of 4,4′‐(buta‐1,3‐diyne‐1,4‐diyl)bis[benzenamine] (APDA; 3 ) with 1‐(2,4‐dinitrophenyl)‐1′‐hexyl‐4,4′‐bipyridinium bromide chloride (1 : 1 : 1) ( 1 ), 1‐(2,4‐dinitrophenyl)‐4‐(pyridin‐4‐yl)pyridinium chloride ( 2 ), or 1‐(2,4‐dinitrophenyl)pyridinium chloride ( 6 ) (Schemes 1 and 2). The anion‐exchange reactions of 8 with NaI and Li(TCNQ) (TCNQ^?=2,2′‐(cyclohexa‐2,5‐diene‐1,4‐diylidene)bis[propanedinitrile] radical ion (1?)) yielded the corresponding I^? and TCNQ^? salts 9 (PyDA(I)) and 10 (PyDA(TCNQ)). Compounds 10 and 4 exhibited a UV/VIS absorption due to a charge transfer between the TCNQ^? and the pyridinium groups and a strong solute–solvent interaction of a dipolar solute molecule in the polar environment, respectively. Compounds 8 – 10 exhibited photoluminescence in solution, whereas 4 and 7 did not because of the presence of the 4,4′‐bipyridinium quenching groups. Differential‐scanning‐calorimetry (DSC) measurements suggested that the DAs obtained in this study can be converted into poly(diacetylenes) by thermal polymerization.     

Synthesis and properties of new ionic liquid crystals based on para-nitroazobenzene with substitution vinylimidazolium ion group

A new series of ionic liquid crystals (ILCs), 1-(4-(4-nitrophenylazo)phenyloxy) vinyl-3-methyl-1H-imidazol-3-ium bromide salts (C _n , n?=?6, 10) were synthesised. Their chemical structures were determined by ¹H NMR, ¹³C NMR, UV spectroscopy and elemental analysis. The liquid crystalline properties were investigated by differential scanning calorimetry, polarising optical microscopy, and powder X-ray diffraction. These measurements showed that C _n (n?=?6, 10) exhibit smectic liquid crystalline phases with focal-conic fan-shaped textures. The introduction of vinylimidazolium group onto the azobenzene enhances the thermal stability of the smectic state, which play an important role in forming the smectic layer structure.     

Rare examples of base pairing via a protonated pyridine N atom in two salts of N2,N6‐bis(1,3‐dimethylimidazolin‐2‐ylidene)pyridine‐2,6‐diamine

The title compounds, namely 2,6‐bis[(1,3‐dimethylimidazolin‐2‐ylidene)amino]pyridinium perchlorate, C₁₅H₂₄N₇⁺·ClO₄⁻, (I), and bis{2,6‐bis[(1,3‐dimethylimidazolin‐2‐ylidene)amino]pyridinium} μ‐oxido‐bis[trichloridoiron(III)], (C₁₅H₂₄N₇)₂[Fe₂Cl₆O], (II), are structurally unusual examples of the organization of molecular units via base pairing. The cations in salts (I) and (II) are derived from the bisguanidine N²,N⁶‐bis(1,3‐dimethylimidazolin‐2‐ylidene)pyridine‐2,6‐diamine, which associates in centrosymmetric pairs via two N—H...N hydrogen‐bond interactions. N—H...N bridges are formed between the protonated pyridine N atom and one of the nonprotonated guanidine N atoms, with N...H distances of 2.01 (1)–2.10 (1) Å. Compound (I) contains two crystallographically independent cations and anions per asymmetric unit. One of the perchlorate anions is disordered, while the [Fe₂Cl₆O]²⁻ anion lies on an inversion centre.     

Molecular structures of 3‐[(2,2,3,3‐tetrafluoropropoxy)methyl]‐ and 3‐[(2,2,3,3,3‐pentafluoropropoxy)methyl]pyridinium saccharinates

The salts 3‐[(2,2,3,3‐tetrafluoropropoxy)methyl]pyridinium saccharinate, C₉H₁₀F₄NO⁺·C₇H₄NO₃S⁻, (1), and 3‐[(2,2,3,3,3‐pentafluoropropoxy)methyl]pyridinium saccharinate, C₉H₉F₅NO⁺·C₇H₄NO₃S⁻, (2), i.e. saccharinate (or 1,1‐dioxo‐1λ⁶,2‐benzothiazol‐3‐olate) salts of pyridinium with –CH₂OCH₂CF₂CF₂H and –CH₂OCH₂CF₂CF₃meta substituents, respectively, were investigated crystallographically in order to compare their fluorine‐related weak interactions in the solid state. Both salts demonstrate a stable synthon formed by the pyridinium cation and the saccharinate anion, in which a seven‐membered ring reveals a double hydrogen‐bonding pattern. The twist between the pyridinium plane and the saccharinate plane in (2) is 21.26 (8)° and that in (1) is 8.03 (6)°. Both salts also show stacks of alternating cation–anion π‐interactions. The layer distances, calculated from the centroid of the saccharinate plane to the neighbouring pyridinium planes, above and below, are 3.406 (2) and 3.517 (2) Å in (1), and 3.409 (3) and 3.458 (3) Å in (2).     

Stabilization of the Pentazolate Anion in Three Anhydrous and Metal‐Free Energetic Salts

According to previous reports, metal cations or water molecules are necessary for the stabilization of pentazolate anion (cyclo‐N₅^?) at ambient temperature and pressure. Seeking a new method to stabilize N₅^? is a big challenge. In this work, three anhydrous, metal‐free energetic salts based on cyclo‐N₅^? 3,9‐diamino‐6,7‐dihydro‐5 H‐bis([1,2,4]triazolo)[4,3‐e:3′,4′‐g][1,2,4,5] tetrazepine‐2,10‐diium, N‐carbamoylguanidinium, and oxalohydrazinium (oxahy⁺) pentazolate were synthesized and isolated. All salts were characterized by elemental analysis, IR spectroscopy, ¹H, ¹³C, and (in some cases) ¹⁵N NMR spectroscopy, thermal analysis (TGA and DSC), and single‐crystal XRD analysis. Computational studies associated with heats of formation and detonation performance were performed by using Gaussian 09 and Explo5 programs, respectively. The sensitivity of the salts towards impact and friction was determined, and overall the real N₅ explosives showed promising energetic properties.     

Chiral Pyrrolidinium Ionic Liquids with (−)-Borneol Fragment in the Cation – Synthesis,Physicochemical Properties and Application in Diels-Alder Reaction

A series of chiral pyrrolidinium salts containing (1 S)-endo-(−)-born-2-yloxymethyl substituent in the structure of the cation and six different anions: chloride, tetrafluoroborate [BF₄]⁻, hexafluorophosphate [PF₆]⁻, trifluoromethanesulfonate [OTf]⁻, bis(trifluoromethylsulfonyl)imide [NTf₂]⁻, bis(pentafluoroethylsulfonyl)imide [NPf₂]⁻ and perfluorobutanesulfonate [C₄FS]⁻ were efficiently prepared and extensively characterized. The enantiomeric purity of them was confirmed by NMR analysis with a chemical shift reagent. All salts were characterized with the specific rotation, the solubility in commonly used solvents, thermal properties, including phase transition temperatures and thermal stability. Salts with [PF₆]⁻, [C₄FS]⁻, [NTf₂]⁻ and [NPf₂]⁻ anions were classified as chiral ionic liquids (CILs). Moreover, salts with [NTf₂]⁻ and [NPf₂]⁻ anions were in the liquid state at room temperature and below. Therefore, density and dynamic viscosity, the surface tension and the contact angle on three different surfaces were also measured for them. Additionally, these chiral ionic liquids were tested as solvents in Diels-Alder reaction.     

Ambient temperature thermotropic liquid crystalline viologen bis(triflimide) salts

Two dicationic salts with bis(triflimide) as counterions exhibited crystal-to-smectic liquid crystalline phase transitions (T _m=41 and 37°C) and smectic-to-isotropic liquid phase transitions (T _i=112, 136°C). They had a broad liquid crystalline phase range (71–99°C) and an excellent range of thermal stability (360–364°C). Their mixtures of various compositions also displayed liquid crystalline properties from r.t. to an extended range of temperatures. They exhibited fluorescence in 1, 2-dimethoxyethane and methanol.     

Synthesis,structure characterization,photoluminescence properties and TD–DFT calculations for two new borates

Due to their rich structural chemistry and wide variety of applications, borate materials have provided a rich area of research. In a continuation of this research, diethylammonium bis(2‐oxidobenzoato‐κ²O¹,O²)borate, C₄H₁₂N⁺·BO₄(C₇H₄O)₂⁻, (1), and propylammonium bis(2‐oxidobenzoato‐κ²O¹,O²)borate, C₃H₁₀N⁺·BO₄(C₇H₄O)₂⁻, (2), have been synthesized by the reaction of boric acid with salicylic acid under ambient conditions. In both structures, the B atom exhibits a slightly distorted tetrahedral environment formed by the bidentate coordination of two salicylate anions via the O atoms of the central carboxylate and oxide groups. In the crystals of salts (1) and (2), mixed cation–anion layers lying parallel to the (101) plane are formed through N—H…O, C—H…O and C—H…π/N—H…O hydrogen‐bonding interactions, resulting, in each case, in a two‐dimensional supramolecular architecture in the solid state. The photoluminescence properties of the salts were studied using the as‐synthesized samples and reveal that salts (1) and (2) both display a strong blue‐light emission, with maxima at 489 and 491 nm, respectively. In DFT/TD–DFT (time‐dependent density functional theory) studies, the blue emission appears to be derived from an intramolecular charge transfer (ICT) excited state. In addition, IR and UV–Vis spectroscopies were used to investigate the title salts.     

Molecular Recognition Properties of Biphen[4]arene

Biphen[n]arenes (n=3, 4) are a new family of macrocyclic hosts. Here, we describe the molecular recognition behavior of hydroxylated biphen[4]arene (OHBP4) for the first time. A series of cationic guests with different sizes and shapes, including quaternary ammonium salts ( 1? PF₆ and 2? PF₆), pyridinium‐based guests ( 3? 2 PF₆– 6? 2 PF₆), and cobaltocenium hexafluorophosphate ( 7? PF₆), were chosen as model guest molecules. OHBP4 exhibits good selectivity towards the 2,7‐dibutyldiazapyrenium bis(hexafluorophosphate) ( 4? 2 PF₆) axle to form a [2]pseudorotaxane‐type complex. In contrast, hydroxylated biphen[3]arene (OHBP3) cannot bind with this big guest. In addition, OHBP4 strongly interacts with adamantane derivative 2? PF₆ and cobaltocenium 7? PF₆, which have tridimensional shape and relatively large size. The association constant of the 7 ⁺?OHBP4 complex in 1:1 (v/v) [D₆]acetone/CD₂Cl₂ solution is up to 3100±300 m ^?1.     

Ionic discotic liquid crystals: synthesis and characterization of pyridinium bromides containing a triphenylene core

Five novel pyridinium salts tethered with hexaalkoxytriphenylene molecules were synthesized by the quaternization of pyridine with ω-bromo-substituted triphenylene derivatives. Their chemical structures were determined by ¹H NMR, ¹³C NMR, IR, UV spectroscopy and elemental analysis. The thermotropic liquid crystalline properties of these salts were investigated by polarizing optical microscopy and differential scanning calorimetry. These triphenylene-based pyridinium salts with bromide as counterion were found to be mesomorphic over a wide temperature range.     

Liquid Crystal and Rheological Behavior of 2,6-Bis(benzylidene)cyclohexanone

The liquid crystalline compound, 2,6-bis(benzylidene)cyclohexanone was synthesized using benzaldehyde and cyclohexanone as raw material, and tetrabutyl ammonium bromide as phase-transfer catalyst in the solution of sodium hydroxide. The effect of several factors, such as reaction time, reaction temperature, and concentration of sodium hydroxide, has been investigated. The product was characterized by infrared spectra, ¹H NMR and elemental analysis. The physicochemical behavior of the crystalline compound was studied by differential scanning calorimetry, polarizing microscope, and rheometer. The experimental results show that the synthesized compound exhibits typical semectic thermot liquid crystal. Meanwhile, the crystal of the compound was determined by x-ray single crystal diffraction analysis. The crystal of the compound belongs to monoclinic system with space group P2(1)/c, a = 9.586(1) Å, b = 18.391(2) Å, c = 9.433(1)Å, α = 90°, β = 115.816(2)°, γ = 90°, Dc = 1.217 g · cm^?3, V = 1496.9(3) Å^?3, and Z = 4.     

New Host Molecules with Imidazoliums as Functional Arms:Syntheses and Anion Recognition

The bridged tri-imidazoliums 3.3X^--5.3X^-(X^-=PF6^-,Br^-,I^-)and bis-imidazoliums 6.2PF6^- were synthesized by N-quaternization of imidazole derivative 1 in acetonitrile under reflux.UV spectroscopic titration experiments showed that the halide salts and hexafluorophosphate salts of these imidazoliums exhibited good recognition toward anions in water and in acetonitrile,respectively.     

Mesomorphic azomethine complexes of Iron(III) based on 4,4′-dodecyloxybenzoyloxybenzoyl-4-salicylidene-2-aminopyridine

A new series of liquid crystalline (LC) complexes Fe(III) based on azomethine 4,4′-dodecyloxybenzoyloxybenzoyl-4-salicylidene-2-aminopyridine with counter-ions PF₆^?, NO₃^?, Cl^?, BF₄^?, ClO₄^?, CNS^? and SO₄^2– was synthesised. According to elemental analysis, FT-IR, ¹H-NMR and mass spectrometry (MALDI ToF), it was found that bi(ligand) Fe(III) complexes were formed with octahedral packing of the metal ion. The presence of the counter-ion in the complexes was confirmed by Infrared spectroscopy. The thermotropic LC properties were investigated by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). All the seven complexes in this series exhibit thermotropic mesophases.     

Geminally Diaurated Aryls Bridged by Semirigid Phosphine Pillars: Syntheses and Electronic Structure

Geminally diaurated μ₂‐aryl complexes have been prepared where gold(I) centers were bridged by the semirigid diphosphine ligands bis(2‐diphenylphosphinophenyl)ether (DPEphos) and 4,6‐bis(diphenylphosphanyl)dibenzo[b,d]furan (DBFphos). Diaurated complexes were synthesized in ligand redistribution reactions of the corresponding di‐gold dichlorides with di‐gold diaryls (six of them new) and silver(I) salts. Diaurated complexes were isolated as salts of the minimally coordinating anions SbF₆^? and ReO₄^?. Efforts to prepare salts of the tetraarylborate [B(3,5‐(CF₃)₂C₆H₃)₄]^? led to transmetalation from boron, with crystallization of the fluorinated aryl complex. The new complexes were characterized by multinuclear NMR, absorption and emission spectroscopies, 77 K emission lifetimes, and by combustion analysis; three are crystallographically characterized. Structures of geminally diaurated aryl ligands are compared to those of mono‐aurated analogues. Both crystal structures and density‐functional theory calculations indicate slight but observable disruptions of aryl ligand aromaticity by geminal di‐gold binding. An intermolecular aurophilic interaction in one structurally authenticated complex was examined computationally.     

Capacity of graphene anode in ionic liquid electrolyte

The graphene anode was investigated in an ionic liquid electrolyte (0.7 M lithium bis(trifluoromethanesulfonyl)imide (LiNTf₂)) in room temperature ionic liquid (N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (MPPyrNTf₂)). SEM and TEM images suggested that the electrochemical intercalation/deintercalation process in the ionic liquid electrolyte without vinylene carbonate (VC) leads to small changes on the surface of graphene particles. However, a similar process in the presence of VC results in the formation of a coating (SEI—solid electrolyte interface) on the graphene surface. During charging/discharging tests, the graphene electrode working together with the 0.7 M LiNTf₂ in MPPyrNTf₂ electrolyte lost its capacity, during cycling and stabilizes at ca. 200 mAh g^?1 after 20 cycles. The addition of VC to the electrolyte (0.7 M LiNTf₂ in MPPyrNTf₂?+?10 wt.% VC) considerably increases the anode capacity. Electrodes were tested at different current regimes: ranging between 50 and 1,000 mA g^?1. The capacity of the anode, working at a low current regime of 50 mA g^?1, was ca. 1,250 mAh g^?1, while the current of 500 mA g^?1 resulted in capacity of 350 mAh g^?1. Coulombic efficiency was stable and close to 95 % during ca. 250 cycles. The exchange current density, obtained from impedance spectroscopy, was 1.3?×?10^?7 A cm^?2 (at 298 K). The effect of the anode capacity decrease with increasing current rate was interpreted as the result of kinetic limits of the electrode operation.     

Asymmetric N-heterocyclic carbene benzimidazolium salts and their silver(I) complexes: potential as ionic liquid crystals

The synthesis and characterisation of a homologous series of monodentate benzimidazolium salts, 1–4 and their mononuclear silver(I)–NHC (where NHC = N-heterocyclic carbene) complexes, 5–8, are reported. The benzimidazolium salts were prepared from the N-alkylation of 1-methyl-benzimidazole with alkyl halides of varying carbon chain lengths. The mono silver(I)-NHC complexes, 5–8, were prepared by the reaction of the benzimidazolium salts with Ag₂O. All the synthesised compounds were fully characterised by ¹H-nuclear magnetic resonance (¹H-NMR), ¹³C-NMR and fourier-transform infrared (FTIR) spectroscopy. The molecular structures of compounds 3·PF₆, 4·PF₆, 7 and 8 were elucidated through single-crystal X-ray diffraction analyses. We postulate that the attachment of long alkyl chains to the heterocyclic core of 1-methyl benzimidazole could induce mesophase formation. The liquid crystalline behaviour of the benzimidazolium salts was investigated by polarised optical microscope and differential scanning calorimetry. Salts 3 and 4 were found to be thermotropic liquid crystals which exhibited a smectic A phase. However, upon complexation with silver(I) ions, all the Ag(I)–NHC complexes are found to be non-mesogenic.