Supramolecular liquid crystals induced by intermolecular hydrogen bonding between benzoic acid and 4-(alkoxyphenylazo) pyridines

Supramolecular liquid crystalline complexes have been obtained from binary mixtures of 4-(alkoxyphenylazo) pyridines and 4-octyloxylbenzoic acid. None of the pyridine-based derivatives is mesomorphic, but the hydrogen-bonded complexes are. Their liquid crystalline properties were investigated by DSC, polarizing optical microscopy, FTIR spectroscopy and powder X-ray diffraction. The complexes exhibit enantiotropic smectic C phases.     

Supramolecular liquid crystals induced by intermolecular hydrogen bonding between benzoic acid and 4-(alkoxyphenylazo) pyridines

Supramolecular liquid crystalline complexes have been obtained from binary mixtures of 4-(alkoxyphenylazo) pyridines and 4-octyloxylbenzoic acid. None of the pyridine-based derivatives is mesomorphic, but the hydrogen-bonded complexes are. Their liquid crystalline properties were investigated by DSC, polarizing optical microscopy, FTIR spectroscopy and powder X-ray diffraction. The complexes exhibit enantiotropic smectic C phases.     

Self-assembled 1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine dimer and its hydrogen-bonded complexes

We report the synthesis and investigation of a new self-assembled benzoylhydrazine-based compound, namely 1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine and their hydrogen-bonded complexes with different carboxylic acid derivatives, of which some exhibit liquid crystalline properties and some are non-mesogens. The conversion of the non-liquid crystalline target compound that is free from carboxylic acid to liquid crystalline complexes containing various carboxylic acids can probably be rationalised through the breaking of intermolecular hydrogen bonding within the supramolecular assembly by carboxylic acid dopants. The enhancement of liquid crystalline properties of benzoylhydrazine compounds with respect to various carboxylic dopants is documented. Other salient features can be exemplified by the formation of discotic columnar phase as shown by the azo-linkage containing 4-(4′-(10-decyloxy)phenylazo)benzoic acid-doped complex.     

New supramolecular liquid crystals induced by hydrogen bonding between pyridyl-1,2,4-oxadiazole derivatives and 2,5-thiophene dicarboxylic acid

Supramolecular liquid crystalline complexes were obtained from binary mixtures of 3-(4-pyridyl)-5-(4-n-alkoxy)phenyl-1,2,4-oxadiazoles and 2,5-thiophene dicarboxylic acid. Although the oxadiazole derivatives and the dicarboxylic acid are non-mesomorphic, the H-bonded complexes exhibit mesomorphism. Their liquid crystalline properties were investigated by differential scanning calorimetry and polarizing optical microscopy. The complexes exhibit enantiotropic nematic phases. A structural study involving AM1 semi-empirical calculations is also described.     

Cationic liposome-nucleic acid complexes: liquid crystal phases with applications in gene therapy

Cationic liposome (CL) carriers of nucleic acids are primarily studied because of their applications in gene delivery and gene silencing with CL-DNA and CL-siRNA (short-interfering RNA) complexes, respectively, and their implications to ongoing clinical gene therapy trials worldwide. A series of synchrotron-based small-angle-x-ray scattering studies, dating back to 1997, has revealed that CL-nucleic acid complexes spontaneously assemble into distinct novel liquid crystalline phases of matter. Significantly, transfection efficiency (TE; a measure of expression of an exogenous gene that is transferred into the cell by the lipid carrier) has been found to be dependent on the liquid crystalline structure of complexes, with lamellar complexes showing strong dependence on membrane charge density (σ(M)) and non-lamellar complexes exhibiting TE behavior independent ofσ(M). The review describes our current understanding of the structures of different liquid crystalline CL-nucleic acid complexes including the recently described gyroid cubic phase of CL-siRNA complexes used in gene silencing. It further makes apparent that the long-term goal of developing optimized liquid crystalline CL-nucleic acid complexes for successful medical applications requires a comprehensive understanding of the nature of the interactions of distinctly structured complexes with cell membranes and events leading to release of active nucleic acids within the cell cytoplasm.     

Mesomorphic behaviour of 4-benzoyloxybenzoic acid and its binary mixture with 4-acetoxybenzoic acid

The nematic liquid crystalline property of 4-benzoyloxybenzoic acid (BBA) was observed by polarizing microscopy and X-ray diffraction. The structure of the hydrogen-bonded BBA dimer was verified by FT-IR, and the axial ratio ( l / d ) of the rod-like molecule was calculated to be 5.8, which is large enough to exhibit a liquid crystalline phase. The mesophase was stable at 240 C. At higher temperatures, for example, 270 C, the trans -esterification side reaction occurred. The binary phase diagram of BBA and 4-acetoxybenzoic acid shows the eutectic temperature at 175 C.     

Synthesis and phase behaviour of hydrogen-bonded liquid crystalline complexes of allyloxybenzoic acid compounds with 4,4'-bipyridine

Three kinds of benzoic acid compounds were synthesized and characterized; the corresponding symmetric hydrogen-bonded liquid crystalline complexes based on these benzoic acid compounds and 4,4'-bipyridine (BPy) were then prepared. The existence of the hydrogen bonds was verified by Fourier transform infrared spectroscopy. The liquid crystalline properties of the complexes were demonstrated by polarizing microscopy and differential scanning calorimetry. 4-Allyloxy-2-fluorobenzoic acid and two fluorinated hydrogen-bonded complexes exhibited only nematic phases, whereas the non-fluorinated complex showed both smectic and nematic phases. The clearing points and mesophase thermal range of the complexes decreased with increasing number of lateral fluorine atoms on the rigid core.     

Hydrogen-bonded liquid-crystalline complexes of polyester containing a pyridyl moiety with 4-(alkoxy)benzoic acid

Novel hydrogen-bonded polyester complexes from mesogenic 4-(butyloxy)benzoic acid (2a), 4-(octyloxy)benzoic acid (2b), 4-(dodecyloxy)benzoic acid (2c) and 4-(tetradecyloxy)benzoic acid (2d) as the hydrogen bond donors and a polyester (3) based on 2,6-pyridine dicarboxylic acid as the hydrogen bond acceptor were prepared by the melt method. The association by hydrogen bonding was confirmed by means of FTIR. The components were miscible up to 0.1 mole ratio of 2d and 2c versus the polyester repeat unit. The limiting mole ratio for 2b and 2a to 3 were 0.2 and 0.4, respectively. Phase separation in the supramolecular complexes occurred above these limiting values and a two phase system consisting of a polyester supramolecular complex and 4-(alkyloxy)benzoic acid was formed. This was due to weak hydrogen bonding between the low molecular acid (especially the acid with longer terminal alkoxy group) and pyridyl unit of polyester in comparison with thermodynamically more favorable dimerization of acid molecules. The liquid crystalline behavior of these supramolecular polymeric complexes was confirmed by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). It was found that 2a exhibits no mesomorphism when mixed with polyester. However, among the other acid derivatives, 2b exhibited stable mesogenic complexes.     

H-Bonded complexes of N, N-disubstituted aminophenylazo-(4)-pyridine and benzoic acid derivatives: preparation, mesogenic study and molecular modelling

N, N-Disubstituted aminophenylazo-(4)-pyridine forms complexes with a series of m-alkoxy benzoic acids by intermolecular hydrogen bonding; liquid crystalline phases of the resulting complexes are thus induced.     

Preparation of new supramolecular liquid-crystalline polyesters containing 3-chloro-4-(alkoxy)benzoic acids

Supramolecular liquid-crystalline polyester complexes based on intermolecular hydrogen bonds between the carboxylic group and the pyridyl moieties was prepared by using non-liquid-crystalline H-donors, [3-chloro-4-(butyloxy)benzoic acid (2a), 3-chloro-4-(octyloxy)benzoic acid (2b), 3-chloro-4-(dodecyloxy)benzoic acid (2c) and 3-chloro-4-(tetradecyloxy)benzoic acid (2d)] and H-acceptor-polyester containing pyridyl units. Intermolecular hydrogen bond formation was confirmed by Fourier transform infrared spectroscopy. The liquid-crystalline behavior of the complex formed was established by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The polyester complexes containing 2c and 2d donor components exhibit liquid crystalline mesophase and behave as side-chain liquid-crystalline polymers. Compared with unsubstituted parent acid, the presence of chloro group as a lateral substituent has a little negative effect on the induction of liquid crystallinity on the polyester complexes systems. The results show that the more stability of the obtained H-bonded complexes in comparison with analogues without 3-Cl substituents is due to the increased acidity of benzoic acid moiety.     

Induction of mesophases through the complexation between benzoic acids with lateral groups and polyamides containing a 2,6-diaminopyridine moiety

Supramolecular liquid crystalline polymeric complexes have been prepared by the complexation of 4-alkyloxybenzoic acid derivatives and polyamides containing a 2,6-diaminopyridine moiety. 4-Alkyloxybenzoic acids substituted by methoxy, methyl, and nitro groups at the 3-position are used for the complexation. These polymeric complexes behave as single component liquid crystalline polymers and exhibit stable and enantiotropic mesophases. In contrast, simple 4-alkyloxybenzoic acids having no substituent at the 3-position, do not form stable complexes with the polymers. For low molecular mass complexes derived from 2,6-bis(acylamino)pyridine and 4-alkyloxybenzoic acid derivatives, substituent effects are different from those for the polymeric system. In these cases, mesomorphic behaviour is observed only for the complexes based on the simple 4-alkyloxybenzoic acid and 4-alkyloxy-3-methylbenzoic acid.     

New supramolecular liquid crystals induced by hydrogen bonding between pyridyl‐1,2,4‐oxadiazole derivatives and 2,5‐thiophene dicarboxylic acid

Supramolecular liquid crystalline complexes were obtained from binary mixtures of 3‐(4‐pyridyl)‐5‐(4‐n‐alkoxy)phenyl‐1,2,4‐oxadiazoles and 2,5‐thiophene dicarboxylic acid. Although the oxadiazole derivatives and the dicarboxylic acid are non‐mesomorphic, the H‐bonded complexes exhibit mesomorphism. Their liquid crystalline properties were investigated by differential scanning calorimetry and polarizing optical microscopy. The complexes exhibit enantiotropic nematic phases. A structural study involving AM1 semi‐empirical calculations is also described.     

Hydrogen-bonded complexes between mesogenic heterocyclic Schiff's bases and mesogenic 4- n -nonyloxybenzoic acid: mesomorphic behaviour, FTIR study and PM3 semi-empirical calculations

A new series of intermolecular hydrogen-bonded complexes has been obtained using mesogenic 4- n -nonyloxybenzoic acid and mesogenic 5-(4-pyridyl)-2-(4- n -alkoxy) benzylideneamino-1,3,4-thiadiazole moieties. The thermal and phase behaviour of these complexes were studied by thermal microscopy and differential scanning calorimetry. Intermolecular hydrogen bonding was studied by FTIR spectroscopy, from crystalline to the isotropic state. A study by PM3 semi-empirical calculations is also described.     

H-Bonded complexes of N,N-disubstituted aminophenylazo-(4)-pyridine and benzoic acid derivatives: preparation,mesogenic study and molecular modelling

N, N-Disubstituted aminophenylazo-(4)-pyridine forms complexes with a series of m-alkoxy benzoic acids by intermolecular hydrogen bonding; liquid crystalline phases of the resulting complexes are thus induced.     

T-型氢键液晶复合物的制备与液晶行为

以不具有液晶行为的2,6-二[N,N′-二-(4-烷基苯甲酰基)]氨基吡啶(A系列)和4-正烷氧基苯甲酸(D系列)作为氢键液晶复合物的单体,组装成T-型氢键液晶系列复合物(AmDn)。用红外光谱对其结构进行了表征,用DSC及偏光显微方法对其液晶行为进行了研究。结果表明:所合成的21种复合物分子间存在氢键且都具有向列相。通过调整2,6-二[N,N′-二-(4-烷基苯甲酰基)]氨基吡啶分子上柔性烷基的长度和极性,可以有效地调节它与4-烷氧基苯甲酸形成的氢键复合物的液晶相变温度以及液晶态的稳定性;增加2,6-二[N,N′-二-(4-烷基苯甲酰基)]氨基吡啶分子上柔性烷基的长度,其复合物AmDn的液晶相温度范围趋于变窄,清亮点逐渐下降,其液晶态稳定性也逐渐下降;以2,6-二[N,N′-二-(4-烷基苯甲酰基)]氨基吡啶分子替代2,6-二[N,N′-二-(4-烷氧基苯甲酰基)]氨基吡啶分子,可以降低分子的极性,使其单体的熔点及其氢键复合物AmDn的相变温度下降。     

Hydrogen-bonded complexes between mesogenic heterocyclic Schiff's bases and mesogenic 4- n -nonyloxybenzoic acid: mesomorphic behaviour,FTIR study and PM3 semi-empirical calculations

A new series of intermolecular hydrogen-bonded complexes has been obtained using mesogenic 4-n-nonyloxybenzoic acid and mesogenic 5-(4-pyridyl)-2-(4-n-alkoxy) benzylideneamino-1,3,4-thiadiazole moieties. The thermal and phase behaviour of these complexes were studied by thermal microscopy and differential scanning calorimetry. Intermolecular hydrogen bonding was studied by FTIR spectroscopy, from crystalline to the isotropic state. A study by PM3 semi-empirical calculations is also described.     

New metallomesogens with enaminoketonato ligands

Several metallomesogens based on enaminoketonato ligands have been prepared. 1-Amino-1-(4'-butoxy-4-biphenyl)oct-1-en-3-one was synthesized by heterocycle hydrogenolysis in 3-(4'-butoxy-4-biphenyl)-5-amyl-isoxazole. Liquid crystalline complexes were obtained by reaction of this enaminoketone with nickel(II) or copper(II) acetates. Hydrogenolysis of the heterocycle in 3-(4-hydroxyphenyl)-5-amylisoxazole led to 1-amino-1-(4-hydroxyphenyl)oct-1-en-3-one. The corresponding copper(II) enaminoketonate was then obtained. The subsequent reaction of this compound with 4-alkoxy-benzoic acid chlorides gave liquid crystalline complexes with ester bridges in the core. A nematic phase was observed for all the synthesized metallomesogens. The bridging group influence on melting points, mesophase ranges and thermal stability of copper(II)complexes is discussed.     

Liquid crystalline polyaniline and phthalocyanine-based polysiloxanes bearing lateral fluoro-substituted benzoic acid groups

A series of novel liquid crystalline polymers (PI, PII, PIII and PIV) containing lateral fluoro-substituted benzoic acid groups was synthesised using cholesteryl 4-(2-propenyloxy)-benzoate, 4-(allyloxy)-3-fluorobenzoic acid and poly(methylhydrogeno)siloxane. PI and PII showed smectic phase, but PIII and PIV showed chiral nematic phase due to more lateral fluoro-substituted benzoic acid groups in the polymer systems. Liquid crystalline polyaniline (PAN) and phthalocyanine (Pc)-based polysiloxanes showing chiral nematic phase were prepared by use of Pc, PAN and these liquid-crystalline polymers via hydrogen bond. PAN-based polysiloxanes showed different liquid crystalline behaviours from Pc-based polysiloxanes due to the difference of molecular structure. PAN-based polysiloxanes showed greater d-spacings between the side mesogenic groups than Pc-based polysiloxanes due to long rod-like geometrical shapes. Hydrogen bond based on lateral fluoro-substituted benzoic acid groups was formed to different geometrical shapes (strip or roundness) between PAN and Pc-based polysiloxanes.     

Ortho-platinated metallomesogens based on rod mesogenic unit of 2-phenylpyridine derivatives: synthesis,high linearly polarised and phase-state-dependent luminescence

Three series of cyclometalated platinum (II) complexes [(cbC_nppyC₁₆) Pt(acac) (a_n), (cbC_nppyC₁₆)Pt(pic) (b_n) and (cbC_nppyC₁₆)Pt(picd) (c_n)] were obtained, where cbC_nppyC₁₆ (2-(4-hexadecyloxyphenyl)-5-[(1,1?-biphenyl)-4-carbonitrile-4?-alkoxy-methoxyl]pyridine) is as cyclometalated ligand, and Hacac (acetylacetone), Hpic (picolinic acid) and Hpicd (5-[(1,1?-biphenyl)-4-carbonitrile-4?-dodecyloxy]oxy-2-car boxylpyridine) are auxiliary, respectively. The liquid crystalline behaviour, polarised emission, photophysical and phase-state-dependent luminescence properties for all platinum (II) complexes were investigated systematically. Cyclometalated platinum (II) complexes b_n show smectic phase structure; however, a_n and c_n show nematic phase. The platinum (II) complexes exhibit different photoluminescence (PL) behaviour in solution, crystal phase, liquid crystal phase and amorphous thin films. Moreover, these metallomesogens show strongly polarised photouminescence in liquid crystalline phases. Especially, the PL dichroic ratio is up to 24.6 in nenatic phase.     

New mesogens with cubic phases: hydrogen-bonded bipyridines and siloxane-containing benzoic acids I. Preparation and phase behaviour

Several 4-(oligodimethylsiloxyl)alkoxybenzoic acids and their hydrogen-bonded complexes with 4,4-dipyridyl or 1,2-bis(4-pyridyl)ethane were prepared and their phase behaviour studied by DSC and polarized optical microscopy. The neat acids showed no liquid crystalline phases. The 4,4-dipyridyl complex of 4-(n-heptamethyltrisiloxyl)hexyloxybenzoic acid (Si3C6BA) exhibits an optically isotropic, highly viscous liquid crystalline phase below a smectic A phase. The 1,2-bis(4-pyridyl)ethane complex of Si₃C₆BA also shows an optically isotropic liquid crystalline phase above its smectic C phase. Its behaviour is similar to that of the well known cubic D phase found in 4-n-alkoxy-3-nitrobiphenyl-4-carboxylic acids. In the hydrogenbonded mesogens studied herein, the cubic phase appears to assemble spontaneously in order to take account of the chemical incompatibility between the siloxane moiety terminating the H-bonded complex and the stiff aromatic cores. The transition temperatures of the cubic phases in these materials is around 100^oC, hence they are amenable to a variety of physical measurements.