Alkoxy Spacer Research Articles

Poly (biphenyl-isatin-piperidine) anion exchange membrane with high hydroxide conductivity based on hydrophilic alkoxy spacer chains

Anion exchange membrane (AEM) with excellent electrical conductivity and high stability has become the main goal of the development of high performance fuel cells. In this work, in order to improve the performance, we will select an effective design strategy with an ether-free (biphenyl-isatin-piperidine) polymer as the main chain. After amination of the chain, the high alkaline resistant piperidine cation serves as a functional group to enhance the alkaline resistance of AEM. At the same time, the hydrophilic flexible spacer chain is introduced to create the phase separation morphology of hydrophilic and hydrophobic water, and to further improve the ion transmission efficiency. It is noteworthy here that PBIP-90-TGM-5 AEM can reach the hydroxide conductivity of 134.21 mS cm−1 at 80 °C, and the prepared PBIP-90-TGM-5 AEM have obvious nanoscale microphase separation morphology, which ensures the membrane has good mechanical properties and dimensional stability. On this basis, PBIP-90-TGM-5 also showed good alkaline stability, and the retention rate was still 81.41 % after 1152 h of 5 M NaOH aqueous solution. At the same time, the peak power density of PBIP-90-TGM-5 at a temperature of 80 °C and an open circuit voltage of 0.94 V can reach 235.7 mW cm−2. This study confirms that poly (biphenyl-isatin-piperidine) has great potential as an AEM for fuel cells.

Discotic liquid crystals with aggregation-induced emission properties based on tetraphenylethylene and triphenylene derivatives

A novel aggregation-induced emission active molecules (TP-Cn-PETPE, n = 4 and 10) were synthesized, which contain a tetraphenylethene derivative as the emission active moiety, a pentahexyloxytriphenylene core as the mesogenic unit and an alkoxy spacer. Experimental results revealed that these two compounds both had AIE properties, even in the liquid state at room temperature. While only TP-C4-PETPE showed a monotropic liquid crystal phase upon heating. In addition, these two compounds were fully characterized by 1H and 13C NMR, IR, EA and MS.

Fast UHPLC enantioseparation of liquid crystalline materials with chiral center based on octanol in reversed-phase and polar organic mode

Fast baseline enantioseparation of twenty racemic liquid crystalline compounds was carried out via ultra-performance liquid chromatography through direct enantioseparation in polar organic and reversed-phase modes. Tris(3-chloro-5-methyl-phenylcarbamate) derivative of amylose was used as chiral stationary phase; the chiral selector was covalently immobilized on sub-2 µm silica particles. Experiments were done using either pure acetonitrile as mobile phase or simple binary mobile phases consisting of acetonitrile/water mixtures in different volume ratios. No buffers or additives were used. Studied materials are a set of structurally similar compounds comprising two different structures of chiral center, various length of alkoxy spacer and four patterns of lateral substitution of aromatic core by fluorine. The compounds do not contain any ionizable group. The effect of the enantiomer structure on the retention and enantioseparation was evaluated. Flow rate and column temperature were optimized as part of method development.

Novel self-cross-linked multi-imidazolium cations long flexible side chains triblock copolymer anion exchange membrane based on ROMP-type polybenzonorbornadiene

A novel benzonorbornadiene derivative (BenzoNBD-Bis(Im+Br−-Im+I−)) grafted by multi-imidazolium cations side-chains combined the rigid alkyl spacer and flexible alkoxy spacer is designed and synthesized. Then, the BenzoNBD-Bis(Im+Br−-Im+I−) monomer is copolymerized with the epoxy functionalized norbornene monomer (NB-MGE) and norbornene (NB) via ring-opening metathesis polymerization (ROMP) using Grubbs 3rd catalyst. All as-designed triblock copolymer membranes (TBCMs) show a thermal decomposition temperature beyond 310 °C and can well be dissolved in common organic solvents. The self-cross-linked structure of anion exchange membrane (AEM) is confirmed by gel fraction and tensile measurement. The water uptake and swelling ratio of TBCMs and AEMs are also measured. Major properties required for AEMs such as ion exchange capacity (IEC), hydroxide conductivity and alkaline stability are investigated. AEM-9.09 shows a hydroxide conductivity of 100.74 mS cm−1 at 80 °C. Besides, the micro-phase separated morphology of AEM is confirmed by TEM, AFM and SAXS analyses, AEMs formed distinct micro-phase separation. The as-prepared AEM exhibits a peak power density of 174.5 mW cm−2 at 365.1 mA cm−2 tested in a H2/O2 single-cell anion exchange membrane fuel cell (AEMFC) at 60 °C. The newly developed strategy of self-cross-linked multi-imidazolium cations long side-chains triblock benzonorbornadiene copolymer provides an effective method to develop high-performance AEMs.

Ultra-performance supercritical fluid chromatography: A powerful tool for the enantioseparation of thermotropic fluorinated liquid crystals

A fast and simple supercritical fluid chromatography method for the enantioseparation of twenty newly synthesized orthoconic antiferroelectric liquid crystals is reported for the first time. The effects of alkoxy spacer length and fluorine atom presence and position in the phenyl ring on chromatographic behavior were investigated. Baseline enantioseparation of all compounds was achieved using simple mobile phases consisting of carbon dioxide and alcohol as cosolvent on (3,5-dimethylphenylcarbamate) derivative of amylose as chiral stationary phase. The analysis times ranged from 2 to 4 and from 4 to 7 min for most samples when using methanol and propane-2-ol, respectively. The significant effect of cosolvent type on the enantioseparation of these compounds was assessed and partial complementarity of methanol and propane-2-ol was observed.

Organic Nanocrystals with Bright Red Persistent Room-Temperature Phosphorescence for Biological Applications.

Persistent room-temperature phosphorescence (RTP) in pure organic materials has attracted great attention because of their unique optical properties. The design of organic materials with bright red persistent RTP remains challenging. Herein, we report a new design strategy for realizing high brightness and long lifetime of red-emissive RTP molecules, which is based on introducing an alkoxy spacer between the hybrid units in the molecule. The spacer offers easy Br-H bond formation during crystallization, which also facilitates intermolecular electron coupling to favor persistent RTP. As the majority of RTP compounds have to be confined in a rigid environment to quench nonradiative relaxation pathways for bright phosphorescence emission, nanocrystallization is used to not only rigidify the molecules but also offer the desirable size and water-dispersity for biomedical applications.

Organic Nanocrystals with Bright Red Persistent Room‐Temperature Phosphorescence for Biological Applications

AbstractPersistent room‐temperature phosphorescence (RTP) in pure organic materials has attracted great attention because of their unique optical properties. The design of organic materials with bright red persistent RTP remains challenging. Herein, we report a new design strategy for realizing high brightness and long lifetime of red‐emissive RTP molecules, which is based on introducing an alkoxy spacer between the hybrid units in the molecule. The spacer offers easy Br−H bond formation during crystallization, which also facilitates intermolecular electron coupling to favor persistent RTP. As the majority of RTP compounds have to be confined in a rigid environment to quench nonradiative relaxation pathways for bright phosphorescence emission, nanocrystallization is used to not only rigidify the molecules but also offer the desirable size and water‐dispersity for biomedical applications.

Radiosynthesis and Preclinical Evaluation of [18F]F-DPA, A Novel Pyrazolo[1,5a]pyrimidine Acetamide TSPO Radioligand, in Healthy Sprague Dawley Rats

PurposeMany neurological conditions result in the overexpression of the translocator protein 18 kDa (TSPO), today recognized as a biomarker for microglial activation and neuroinflammation imaging. The pyrazolo[1,5-a]pyrimidine acetamides are a particularly attractive class of TSPO-specific ligands, prompting the development of several positron emission tomography (PET) radiotracers. This includes F-DPA, a recently reported fluorinated ligand (Ki = 1.7 nM), wherein the fluorine atom is directly linked to the phenyl moiety without the presence of an alkyl or alkoxy spacer chain. Reported here is the preparation of [18F]F-DPA using [18F]Selectfluor bis(triflate) and the preliminary evaluation of [18F]F-DPA in healthy rats. Its metabolic profile and biodistribution in rats are compared with that of [18F]DPA-714, a closely related structure.Procedures[18F]F-DPA was synthesized by electrophilic fluorination using [18F]Selectfluor bis(triflate), [18F]DPA-714 was synthesized by conventional nucleophilic fluorination. The biodistribution of both radiotracers was compared in Sprague Dawley rats. Radiometabolites of both radiotracers in plasma and brain homogenates were analyzed by radioTLC.ResultsThe radiochemical yield of [18F]F-DPA was 15 ± 3 % and the specific activity was 7.8 ± 0.4 GBq/μmol. The radiochemical purity exceeded 99 %. The in vivo time activity curves of [18F]F-DPA demonstrate rapid entry into the brain and a concentration equilibrium at 20–30 min after injection. The metabolic profiles at 90 min after radiotracer injection in the plasma show that unchanged [18F]F-DPA and [18F]DPA-714 account for 28.3 ± 6.4 and 11.1 ± 2.6 % of the remaining radioactivity, respectively. In the brain, unchanged [18F]F-DPA accounts for 93.5 ± 2.8 % of the radioactivity; whereas for [18F]DPA-714, this value is 53.6 ± 1.6 %.Conclusions[18F]Selectfluor bis(triflate) was successfully used to label F-DPA with fluorine-18. The labeling position on the aromatic moiety imparts a higher stability compared to [18F]DPA-714 with regard to in vivo metabolism. [18F]F-DPA is a promising new radiotracer and warrants further investigation in animal models of disease.

Cyanobiphenyl versus Alkoxybiphenyl: Which Mesogenic Unit Governs the Mesomorphic Properties of Guanidinium Ionic Liquid Crystals?

A series of phenylguanidinium salts 3·X, which are linked via an alkoxy spacer either to a 4-decyloxy- or 4-cyano-substituted biphenyl mesogen, was prepared and the mesomorphism studied. A decyloxybiphenyl core and a spacer of at least C6 chain length were required for mesophase formation. Replacement of the chloride counterion by other anions like bromide or tetrafluoroborate improved the thermal stability of the mesophase. A comparison of substitution pattern (meta v. para) on the phenyl ring revealed decreased melting and clearing points for the bent cationic head group. All guanidinium ionic liquid crystals 3 displayed only smectic A (SmA) phases. A packing model is assumed where the molecules in a bilayer stack over each other in opposite direction with interdigitated terminal decyloxy groups and spacers.

Polydentate ligands based on closo-decaborate anion for the synthesis of gadolinium(iii) complexes

A reaction of the closo-decaborate anion 1,4-dioxane derivative with polyatomic alcohols (ethyleneglycol, glycerol, triethanolamine) was studied. These reactions include the ring opening of the cyclic substituent and the addition of the alcohol molecule to boron cluster through the alkoxy spacer chain. The products obtained form coordination compounds upon the reaction with gadolinium(iii) salts, playing the role of polydentate ligands. The compounds obtained were studied by IR spectroscopy, NMR spectroscopy, ESI mass spectrometry, elemental and thermographic analysis.

Towards room temperature ionic liquid crystals: linear versus bent imidazolium phenylpyrimidines

The synthesis and the mesomorphic properties of novel imidazolium salts with mesogenic 2-phenylpyrimidine or 2-alkylpyrimidinecarboxylic acid central cores are reported. The mesogenic units are connected to the imidazolium head groups via an alkoxy spacer. In order to adjust the mesomorphic properties the length of the alkoxy spacer and the terminal alkyl group, the counter ion, the substitution pattern of the imidazolium head group and the molecular geometry (linear vs. bent) are varied and the corresponding compounds were investigated in detail using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray scattering (WAXS, SAXS). Whereas SmA phases with monolayer orientation were observed for imidazolium salts with short N-substituents (R = CH3, C4H9) at the imidazolium head group, the corresponding derivatives with longer N-substituents (R = C12H25, C12H25OC6H4) displayed SmA phases with bilayer orientation irrespective of a linear or bent geometry. For two derivatives, p-5(10,8) and p-5(12,8), a SmC phase was observed. Indeed, bending of the mesogenic core led to a shift of the mesophases towards lower temperatures. Several of the meta-2-phenylpyrimidine derivatives as well as 2-pyrimidine carboxylates displayed melting points below 50 °C. For 2-pyrimidine carboxylates replacement of a bromide anion by triflate resulted in a further decrease of the melting transition close to ambient temperature.

Liquid crystalline imidazolium salts bearing 5-phenylpyrimidine: dependence of mesomorphic properties on spacer lengths, terminal N-alkyl group and counterions

New imidazolium salts bearing substituted 5-phenylpyrimidine mesogenic groups were synthesised and their mesomorphic properties were studied by differential scanning calorimetry, optical microscopy and powder X-ray diffraction methods (WAXS, SAXS). The parent 5-phenylpyrimidines with the terminal bromide group at the alkoxy spacer exhibited low clearing points and smectic mesophases in narrow temperature ranges. The incorporation of the N-alkylimidazolium cationic core, connected with 5-phenylpyrimidine via an alkoxy spacer, remarkably improved the stability of the mesophases. The imidazolium salts with 5-phenylpyrimidine group formed smectic A phases, stable over broad temperature intervals. The influences of the counteranion, the length of terminal alkyl group and alkoxy spacer on the mesomorphic behaviour of the 5-phenylpyrimidine substituted N-alkylimidazolium salts were investigated in detail.

Enhanced Photoluminescence, Mesomorphism and Conformation of Liquid-Crystalline Conjugated Polymers with Terphenyl Mesogen Pendants

A variety of LCCPs containing terphenyl pendants based on polyacetylene, polythiophene, poly(p-phenylene) and a poly(p-phenylene) copolymer backbone have been synthesized. The effects of the structural variation on their properties, especially their mesomorphism, photoluminescence and secondary structures, were studied systematically. Longer alkoxy spacer favor stronger light emission and better mesomorphism. Disubstituted polyacetylenes show better developed mesomorphic textures, higher quantum yields and better thermal stability than their corresponding monosubstituted analogs. Steric effects and the “jacket- effect” from the mesogens cause the bulky terphenyl mesogen pendants to rotate around the main chain and force the main chain to assume a spiral conformation along the main chain in long range.

An Influence of the Fluorosubstitution and the Spacer Length on the Phase Transitions and Helical Pitch Value in High Tilted Antiferroelectric Esters

Phase transitions temperatures and temperature dependence of helical pitch p for S-(+)-4′-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[(4,4,4,3,3,2,2-heptafluorobutoxy)alkoxy] benzoates, and 3-fluoro-, and 2-fluoro-, 2,3-difluoro-benzoates upon length of alkoxy spacer were tested. For etoxy and propoxy spacer the pitch p in antiferroelectric phase is increasing with temperature to maximal value of about 1000 nm in high temperatures region. For pentoxy, hexoxy, and heptoxy spacer the pitch p is longer and reverse temperature dependence is observed. The compounds convenient for formulation of antiferroelectric orthoconic mixture with pitch length of about 2000 nm were selected.

Microwave-assisted synthesis and liquid crystal properties of 1,3,4-thiadiazole-based liquid crystals

A series of 2-(4-alkoxyphenyl)-5-p-tolyl-1,3,4-thiadiazole derivatives 2a–2h were synthesised efficiently under microwave irradiation and solvent-free conditions. The thermal properties were determined using polarised optical microscopy (POM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). All these compounds exhibited enantiotropic liquid crystal properties with wide mesomorphic temperature ranges and good thermal stability. Compounds 2a–2f with short alkoxy chain (n = 1–6) all exhibited an enantiotropic nematic mesophase, while both nematic and smectic C mesophases were observed in compounds 2g (n = 7) and 2h (n = 8) with longer alkoxy spacer. The effect of the length of the alkoxy chain on liquid crystal properties is discussed in this paper.

Photo- and electroluminescent properties of cyano-substituted styryl derivatives and synthesis of CN–PPV model compounds containing an alkoxy spacer for OLEDs

The series of cyano-substituted model compounds 18–20 for organic light emitting diodes (OLEDs) was prepared through Knoevenagel condensation reactions between the dialdehydes 3,6,9 and the differently substituted acetonitrile derivatives 11,16,17. The influence of the different substituents on the optical properties of the resulting α-cyanostyryl compounds 18–20 was investigated. Another series of dimeric cyano-substituted styryl compounds 26–28 were prepared, in which a flexible, nonconjugated spacer is present between the two cyanostyryl moieties. The spacer isolates the π-conjugated portions of dimeric compounds 26–28, improves their solubility in common organic solvents, and decreases their tendency to crystallize. These features are favorable for producing efficient luminescent films in OLEDs devices.

Electrogenerated poly(thiophenes) derivatized by bipyridine ligands and metal complexes

The synthesis of a series of bithiophenic precursors of electrogenerated conjugated polymers functionalized by bipyridine ligands is described. The precursor structure involves two polymerizable groups attached at both ends of a bipyridine ligand and fixed at an internal β-position of thiophene via an alkylsulfanyl or alkoxy spacer. Electrochemical and optical data show that the low polymerization potential resulting from the association of 3,4-ethylenedioxythiophene (EDOT) and alkylsulfanyl or alkoxy thiophene combined with the multi-site polymerization approach allows a straightforward electrosynthesis of extensively conjugated and stable functionalized polymers. On the basis of these results, iron and ruthenium complexes of these precursors have been synthesized and electropolymerized. The analysis of the electrochemical behavior of the resulting polymers shows that they exhibit the typical electrochemical signature of both the conjugated polythiophene backbone and the immobilized metal complex.

Liquid crystalline properties of unsegmented and segmented polyurethanes synthesised from high aspect ratio mesogenic diols

AbstractA series of novel tetrad high aspect ratio mesogenic diol monomers 4‐{[4‐(n‐hydroxyalkoxy)‐phenylimino]‐methyl}‐benzoic acid 4‐{[4‐(n‐hydroxyalkoxy)‐phenylimino]‐methyl}‐phenyl ester were prepared with varying alkoxy spacer length (n=2,4,6,8,10) by reacting 4‐formylbenzoic acid 4‐formylphenyl ester and 4‐(n‐hydroxyalkoxy) anilines. Two series of thermotropic main chain liquid crystalline unsegmented polyurethanes (PUs) were obtained by the polyaddition of the mesogenic diols with hexamethylene diisocyanate (HMDI) and methylene bis(cyclohexylisocyanate) (H12MDI) in dimethylformamide respectively. The effect of the incorporation of a third component namely polyol on the liquid crystalline properties of the polyurethanes was also studied. Linear segmented PUs were synthesised by a two‐step block copolymerisation method. The PUs synthesised were based on six spacer mesogenic diol chain extender, soft segments poly(tetramethylene oxide)glycol (PTMG) (Mn= 650,1000,2000) and polycaprolactone diol (PCL) (Mn=530,1250,2000) of varying molecular weights and different diisocyanates including HMDI, H12MDI and methylene bis(phenylene isocyanate) (MDI). Structural elucidation was carried out by elemental analysis, fourier transform infra red (FT‐IR), nuclear magnetic resonance (1H NMR and 13C NMR) spectroscopy. Inherent viscosity of the unsegmented polymers measured in methanesulphonic acid at 26°C was in the range of 0.13 ‐ 0.65 dL/g while the molecular weights and molecular weight distribution of the segmented polyruethanes was determined using gel permeation chromatography (GPC). Mesomorphic properties were studied by differential scanning calorimetry (DSC) and hot stage polarising optical microscopy and the thermal stability was determined by thermogravimetric(TG)analysis. The monomeric diols and the polyurethanes exhibited nematic texture and good mesophase stability. It was observed that the partial replacement of the mesogenic diol by the polyol of varying molecular weights influenced the phase transitions and the occurrence of mesophase textures. The phase transition temperatures of the investigated polyurethanes showed dependence on the chain length of the soft segment and on the content of the mesogen moiety. A higher content of mesogenic moiety was needed to obtain liquid crystalline property when the soft segment length was increased as observed in the case of PTMG. Grained and threaded textures were observed depending on the molecular weight of the soft segment, the mesogen content and the diisocyanate. The stress‐strain analyses showed that the polymers bused on high molecular weight PTMG soft segment have elastomeric property while the PCL based PUs displayed no elastomeric property.

Synthesis and Characterization of Thermotropic Liquid Crystalline Main-Chain Polyurethanes from High-Aspect Ratio Mesogenic Diols

A series of novel tetrad high aspect ratio mesogenic diol monomers 4-{[4-(n-hydroxyalkoxy)phenylimino]methyl}benzoic acid 4-{[4-(n-hydroxyalkoxy)phenylimino]methyl}phenyl ester (3 a–e) were prepared with varying alkoxy spacer length (n = 2, 4, 6, 8, 10) by reacting 4-formylbenzoic acid 4-formylphenyl ester and 4-(n-hydroxyalkoxy)anilines. Two series of thermotropic main-chain liquid crystalline polyurethanes (LCPUs) 4 a–e and 5 a–e were obtained by the polyaddition of 3 a–e with hexamethylene diisocyanate (HMDI) and 4,4′-methylene bis(cyclohexylisocyanate) (H12MDI) in DMF respectively. Structural elucidation was carried out by elemental analysis, FT-IR, 1H NMR and 13C NMR spectroscopy. Inherent viscosity of the polymers measured in methanesulfonic acid at 26°C was in the range of 0.13–0.65 dL/g. Mesomorphic properties were studied by differential scanning calorimetry and hot stage polarizing optical microscopy and the thermal stability was determined by thermogravimetric analysis. The monomeric diols and the polyurethanes exhibited nematic texture.

Synthesis and properties of novel polyurethanes containing the mesogenic moiety of α-methylstilbene derivatives

4,4 ′-Bis(ω-hydroxyalkoxy)-α-methylstilbene with various spacer lengths (HMS n, where “ n” is the carbon number of the hydroxyalkoxy group) and two series of novel thermotropic liquid crystalline polyurethanes containing the mesogenic core of 4,4 ′-bis(ω-hydroxyalkoxy)-α-methylstilbene were synthesized. One series was obtained by polyaddition reaction of 2,4-toluene diisocyanate (2,4-TDI) with HMS n, denoted as TDI n, and the other was obtained by the reaction of 4,4 ′-diphenylmethane diisocyanate (MDI) with HMS n, denoted as MDI n. The polyurethanes were investigated by IR spectroscopy, DSC, wide angle X-ray diffraction, polarizing microscope and thermogravimetric analysis. All the polyurethanes except for TDI11 exhibited enantiotropic smectic phases which are not similar to those of corresponding HMS n. The transition temperatures and the temperature ranges of mesophases changed with the length of alkoxy spacer and the kind of diisocyanate. The thermal degradation behaviours under nitrogen atmosphere depend on the spacer length but not much on the diisocyanate moiety.