Preliminary communication Properties of nonlinear supramolecular liquid crystals containing thiophenedicarboxylic acids

Novel mesogenic supramolecules have been constructed from the 2 :1 molar ratio of trans 4-alkoxy-4-stilbazoles CnPS (1) complexed with 2,5-thiophenedicarboxylic acid THDA (4) to form the kinked hydrogen-bonded (H-bonded) complexes (CnPS)-THDA. The analogous H-bonded complexes (CnPP)2-THDA consisting of the 2:1 molar ratio of 4-alkoxypyridines CnPP (2) and THDA (4) are also compared. In contrast to linear complexes (CnPS)2-TA prepared from the 2 :1 molar ratio of CnPS (1) and terephthalic acid TA (5), supramolecular liquid crystals with kinked molecular structures (CnPS)2-THDA are generated by introducing the thiophene unit into the H-bonded complexes. In addition, the chiral complex (C5*PS)2-THDA composed of an optically active proton acceptor (S)-(-)-4-(2-methylbutoxy)-4-stilbazole C5*PS ( 3 ) and THDA ( 4 ) (2 :1 molar ratio) is reported. Significantly, the first thiophene based supramolecular liquid crystals have been constructed in this study, and the mesogenic properties of the supramolecules can be easily adjusted not only by the nonlinear shape of the thiophene unit but also by the dipole moment derived from the lone-pair electrons of the sulphur hetero-atom.     

Fused-ring and linking group effects of proton donors and acceptors on simple H-bonded liquid crystals

Two fused-ring structures, 6-decyloxy-2-naphthoic acid C₁₀ONA (3) and 6-dodecyloxyisoquinoline IS (8), were synthesized and utilized as proton donor and acceptor moieties to construct a series of simple mesogenic supramolecules. The other complementary hydrogen-bonded (H-bonded) moieties are benzoic acids, thiophenecarboxylic acid and pyridines containing different alkyl chain lengths connected by ether and ester linkages, i.e. 4-alkoxybenzoic acid C_nOBA (1), terephthalic acid monoalkyl ester C_nCOOBA (2), 2,5-thiophenedicarboxylic acid monodecyl ester C₁₀COOTHA (4), 4-alkoxypyridine C_nOP (6) and isonicotinic acid alkyl ester C_nCOOP (7). Several series of simple mesogenic supramolecular dimers were constructed from 1:1 molar ratios of proton donors (C_nOBA, C_nCOOBA, C₁₀ONA and C₁₀COOTHA) and proton acceptors (IS, C_nOP and C_nCOOP), though the proton acceptor C_nCOOP induced phase separation in all complexes. In order to investigate their fused-ring and linking group effects on the mesogenic properties of the H-bonded complexes, analogous simple supramolecular structures are compared. Supramolecular architecture and the distinct mesomorphism of these simple H-bonded liquid crystalline materials were confirmed by polarizing optical microscopy, DSC and powder X-ray diffraction experiments.     

Supramolecular liquid crystals containing isoquinoline hydrogen-bonded acceptors

6-Dodecyloxyisoquinoline IS ( 1 ) has been synthesized and utilized as a proton acceptor to generate a series of novel mesogenic supramolecules. Two mesogenic supramolecular dimers IS-OBA and IS-COOBA have been constructed from a 1:1 molar ratio of IS complexed either with 4-decyloxybenzoic acid OBA ( 2 ) or with 4-decyloxycarbonylbenzoic acid COOBA ( 3 ). A kinked mesogenic supramolecular trimer, i.e. a double H-bonded complex (IS)-THDA, has been constructed from a 2:1 molar ratio of IS complexed with 2,5-thiophenedicarboxylic acid THDA ( 4 ). The mesogenic properties of the H-bonded complex (IS2)-THDA are compared with those of previously reported H-bonded complexes (C12PS)-THDA and (C12PP2)-THDA consisting of a 2:1 molar ratio of trans -4-dodecyloxy-4-stilbazole C12PS 2 ( 5 ) or 4-dodecyloxypyridine C12PP2 (6 ) with THDA. Significantly, the first isoquinoline-based supramolecular liquid crystals have been built, and their mesogenic properties have been introduced or modified by fused- N -heterocyclic rings.     

Fused-ring and linking group effects of proton donors and acceptors on simple H-bonded liquid crystals

Two fused-ring structures, 6-decyloxy-2-naphthoic acid C₁₀ONA (3) and 6-dodecyloxyisoquinoline IS (8), were synthesized and utilized as proton donor and acceptor moieties to construct a series of simple mesogenic supramolecules. The other complementary hydrogen-bonded (H-bonded) moieties are benzoic acids, thiophenecarboxylic acid and pyridines containing different alkyl chain lengths connected by ether and ester linkages, i.e. 4-alkoxybenzoic acid C _n OBA (1), terephthalic acid monoalkyl ester C _n COOBA (2), 2,5-thiophenedicarboxylic acid monodecyl ester C₁₀COOTHA (4), 4-alkoxypyridine C _n OP (6) and isonicotinic acid alkyl ester C _n COOP (7). Several series of simple mesogenic supramolecular dimers were constructed from 1:1 molar ratios of proton donors (C _n OBA, C _n COOBA, C₁₀ONA and C₁₀COOTHA) and proton acceptors (IS, C _n OP and C _n COOP), though the proton acceptor C _n COOP induced phase separation in all complexes. In order to investigate their fused-ring and linking group effects on the mesogenic properties of the H-bonded complexes, analogous simple supramolecular structures are compared. Supramolecular architecture and the distinct mesomorphism of these simple H-bonded liquid crystalline materials were confirmed by polarizing optical microscopy, DSC and powder X-ray diffraction experiments.     

Synthesis and optical behaviour of hydrogen-bonded liquid crystals based on a chiral pyridine derivative

Three series of cholesteryl-containing supramolecular hydrogen-bonded (H-bonded) liquid crystal (LC) complexes with different number of fluoro-substituent were synthesised and characterised. Cholesteryl isonicotinate as proton acceptor and 4-n-alkoxybenzoic acids with or without fluoro-substituent as proton donor had been mixed in tetrahydrofuran to obtain H-bonded LC complexes. The effect of lateral substitution and the length of terminal chain in the H-bonded precursors on the formation of the supramolecular complexes had been examined. It was found that the introduction of fluoro substituent on the induced mesogens could widen the molecular width and thus reduce the molecular aspect ratio of the complexes, therefore it could lead to compress the formation of the LCs. However, the fluoro substituent played a positive role in enhancing the intermolecular interactions and stabilising the H-bond structure of the complexes. The influence of terminal length on the mesogenic behaviours is also discussed. On increasing the spacer length, the clear point and the thermal range of induced mesophase-like cholesteric phase decreased, and an induced chiral smectic phase began to appear in some complexes with long terminal tails.     

Non-covalent dendrimer-based liquid crystalline complexes: Synthesis and characterization

The synthesis and structural characterization of dendritic macromolecules based on 3,5-dihydroxybenzoic acid are described. The molecular structures and purity of all new compounds were confirmed by ¹H NMR, ¹³C NMR spectroscopy and elemental analysis. The dendritic non-covalent liquid crystalline complexes were prepared through the formation of hydrogen bonds between different generation of dendritic acids (proton donor) and stilbazole derivative containing bipyridyl units (proton acceptor). We found that, the hydrogen-bonded dendritic liquid crystals supramolecules (G1-2py, G2-2py and G3-2py) exhibits nematic and semectic phase. The polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) were used for investigation of the liquid crystalline properties of the hydrogen-bonded dendritic supramolecular complexes.     

Aggregation dependent fluorescence switching in benzothiazole derivative based H-bonded mesogen

In this work, hydrogen-bonded liquid crystal exhibiting phase dependent fluorescence has been reported. The H-bonded materials were prepared using pyridenyl benzothiazole and alkoxy benzoic acid as H-bond acceptor and donor respectively. The formation of the target materials was confirmed via different spectroscopic technique and their mesogenic behaviour has been studied through polarising optical microscope, differential scanning calorimetry and 2D-X-ray diffraction. The H-bonded mesogenic material showed aggregation dependent fluorescence switching when subjected to transformation from isotropic-nematic-crystalline phase sequence. Computational studies were performed to probe into fluorescence switching behaviour of the mesogenic material.     

Supramolecular side chain liquid crystalline polymers assembled via hydrogen bonding between carboxylic acid-containing polysiloxane and azobenzene derivatives

Supramolecular side chain liquid crystalline polymers were prepared from poly(3-carboxypropylmethylsiloxane) (PSI100) and azobenzene derivatives through intermolecular hydrogen bonding (H-bonding) between the carboxylic acid groups in the PSI100 and the imidazole rings in the azobenzene derivatives. The existence of H-bonding has been confirmed using FTIR spectroscopy. The polymeric complexes behave as liquid crystalline (LC) polymers and exhibit stable mesophases. The LC behaviour of these H-bonded polymeric complexes was investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. The complexes exhibit nematic LC phases identified on the basis of Schlieren optical textures. On increasing spacer length or the concentration of the H-bonded mesogenic unit in the complex, the clearing temperature and the temperature range of the LC phase of the polymeric complex increase. The terminal group plays a critical role in determining the LC properties of the polymeric complexes. A terminal methoxy group is more efficient than a nitro group in increasing the clearing temperature. The electron donor-acceptor interactions between the H-bonded mesogenic units containing methoxy and nitro terminal groups in supramolecular 'copolymeric' complexes lead to an increase in the clearing temperature and a wider temperature range for the LC phase.     

Supramolecular side chain liquid crystalline polymers assembled via hydrogen bonding between carboxylic acid-containing polysiloxane and azobenzene derivatives

Supramolecular side chain liquid crystalline polymers were prepared from poly(3-carboxypropylmethylsiloxane) (PSI100) and azobenzene derivatives through intermolecular hydrogen bonding (H-bonding) between the carboxylic acid groups in the PSI100 and the imidazole rings in the azobenzene derivatives. The existence of H-bonding has been confirmed using FTIR spectroscopy. The polymeric complexes behave as liquid crystalline (LC) polymers and exhibit stable mesophases. The LC behaviour of these H-bonded polymeric complexes was investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. The complexes exhibit nematic LC phases identified on the basis of Schlieren optical textures. On increasing spacer length or the concentration of the H-bonded mesogenic unit in the complex, the clearing temperature and the temperature range of the LC phase of the polymeric complex increase. The terminal group plays a critical role in determining the LC properties of the polymeric complexes. A terminal methoxy group is more efficient than a nitro group in increasing the clearing temperature. The electron donor-acceptor interactions between the H-bonded mesogenic units containing methoxy and nitro terminal groups in supramolecular 'copolymeric' complexes lead to an increase in the clearing temperature and a wider temperature range for the LC phase.     

具有形状记忆性能的P(MMA-co-HEA)/PDMS-OH氢键复合物的研究

选择低分子量端羟基聚二甲基硅氧烷(PDMS-OH)与聚(甲基丙烯酸甲酯-co-丙烯酸β-羟乙酯)P(MMA-co-HEA)共聚物原位复合形成氢键复合物,该复合物表现出良好的形状记忆效应.通过FTIR,SEM对材料的结构和形貌进行表征,DMA表征材料的动态力学行为,并通过弯曲实验对材料的形状记忆性能进行了表征及比较.FTIR分析证明PDMS-OH与P(MMA-co-HEA)共聚物形成氢键缔合作用;SEM分析显示,随着PDMS-OH含量的升高,氢键复合物由"海-岛"相分离结构向反转相分离结构转变;DMA分析结果表明,氢键的引入有利于复合物获得更高的模量比;形状记忆性能测试结果显示该氢键复合物具有良好的形状记忆性能,形状记忆固定率超过98%、形变恢复率超过99%,并且与聚(甲基丙烯酸甲酯-co-丙烯酸乙酯)/PDMS-OH(P(MMA-co-EA)/PDMS-OH)复合物相比,氢键复合物显示出更快的形变回复速率.     

Novel single-crystal-to-single-crystal anion exchange and self-assembly of luminescent d(10) metal (Cd(II), Zn(II), and Cu(I)) complexes containing C(3)-symmetrical ligands

Ligands L1 and L2' (L1=N,N',N'-tris(4-pyridyl)trimesic amide, L2'=N,N',N'-tris(3-pyridinyl)-1,3,5-benzenetricarboxamide) belonging to an interesting family of tripyridyltriamides with C(3)-symmetry have been utilized to construct 3D porous or hydrogen-bonded frameworks. Through a novel single-crystal-to-single-crystal anion-exchange process, [Cd(L1)(2)(ClO(4))(2)](n) (1c) can be obtained from [Cd(L1)(2)Cl(2)](n) (1b) in the presence of ClO(4)(-) anions. This anion-exchange process is highly selective and only the substitution of Cl(-) by ClO(4)(-) or PF(6)(-) could be realized; Cl(-) was found not to be substituted by BPh(4)(-). This demonstrates that the exchange process depends on the size of the anions in relation to the size of the cavities in the host material (ca. 7.5 A). In addition, the anion-exchange properties of 1 b have also been investigated by means of powder X-ray diffraction (PXRD), elemental analysis (EA), and infrared absorption spectroscopy (IR). Structurally, [Zn(L1)(NO(3))(2)](n)(2) consists of a 2D coordination network with five-coordinate Zn(II) ions. Surprisingly, different trigonal-bipyramidal Zn(II) ions propagate to form distinct respective sheet structures, A and B, which are packed in an A-B-A-B manner in the crystal lattice, and these are hydrogen-bonded to give a 3D extended framework. The molecular structure of [CuI(L2')](n)(3) shows that the Cu(I) ion adopts a distorted tetrahedral geometry, and 3 also forms a 2D coordination network. Significantly, this 2D coordination network is further assembled into a remarkable 3D homochiral framework through triple hydrogen bonding and pi...pi interactions. All of these 3D coordination polymers and/or hydrogen-bonded frameworks are luminescent in the solid state, and their solid-state luminescent properties have been investigated at room temperature and/or at 77 K.     

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.     

Chiroptical nanofibers generated from achiral metallophthalocyanines induced by diamine homochirality

Optically active cofacial π-π phthalocyanine (Pc) stacked supramolecules were spontaneously and successfully generated from a mixture of four possible geometric isomers (C(4h), D(2h), C(2v), C(s)) of achiral 4(5),4'(5'),4'(5'),4'(5')-tetracarboxymetallophthalocyanine (tcPcM; M=Ni, Cu) induced by an equimolar amount of inexpensive chiral diamine molecular sources in DMSO/CHCl(3) mixed solvent under optimized conditions of the volume ratio of poor/good cosolvents, the molar ratio of chiral molecular diamine to tcPcM, the cavity metal of phthalocyanine, and the addition order of the amines. The sign and amplitude of circular dichroism spectra due to the supramolecular chirality and structure of the diamine molecules are impossible to remove by additions of the antipode diamine and trifluoroacetic acid. The chiral diamine was partly contained in nanofibers, and that retained in the solution can be recycled and reused to induce optically active tcPcM supramolecules.     

Hydration and stability of nucleic acid bases and base pairs

Empirical, quantum chemical calculations and molecular dynamics simulations of the role of a solvent on tautomerism of nucleic acid bases and structure and properties of nucleic acid base pairs are summarized. Attention was paid to microhydrated (by one and two water molecules) complexes, for which structures found by scanning of empirical potential surfaces were recalculated at a correlated ab initio level. Additionally, isolated as well as mono- and dihydrated H-bonded, T-shaped and stacked structures of all possible nucleic acid base pairs were studied at the same theoretical levels. We demonstrate the strong influence of a solvent on the tautomeric equilibrium between the tautomers of bases and on the spatial arrangement of the bases in a base pair. The results provide clear evidence that the prevalence of either the stacked or hydrogen-bonded structures of the base pairs in the solvent is not determined only by its bulk properties, but rather by specific hydrophilic interactions of the base pair with a small number of solvent molecules.     

On differences between hydrogen bonding and improper blue-shifting hydrogen bonding.

Twenty two hydrogen-bonded and improper blue-shifting hydrogen-bonded complexes were studied by means of the HF, MP2 and B3LYP methods using the 6-31G(d,p) and 6--311 ++G(d,p) basis sets. In contrast to the standard H bonding, the origin of the improper blue-shifting H bonding is still not fully understood. Contrary to a frequently presented idea, the electric field of the proton acceptor cannot solely explain the different behavior of the H-bonded and improper blue-shifting H-bonded complexes. Compression of the hydrogen bond due to different attractive forces-dispersion or electrostatics--makes an important contribution as well. The symmetry-adapted perturbation theory (SAPT) has been utilized to decompose the total interaction energy into physically meaningful contributions. In the red-shifting complexes, the induction energy is mostly larger than the dispersion energy while, in the case of blue-shifting complexes, the situation is opposite. Dispersion as an attractive force increases the blue shift in the blue-shifting complexes as it compresses the H bond and, therefore, it increases the Pauli repulsion. On the other hand, dispersion in the red-shifting complexes increases their red shift.     

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.     

A combined quantum chemical/molecular mechanical study of hydrogen-bonded systems

A computational approach, which involves the combination of the OPLS force field and molecular orbital MNDO , AM 1, and PM 3 methods, has been developed to describe the effects of a large, molecular mechanically simulated environment on the Hamiltonian of a quantum chemical system. To test the validity of the combined quantum mechanical/molecular mechanical (QM /MM ) potential, a systematic study of the structures and energies of neutral and charged hydrogen-bonded complexes has been carried out, including comparisons with pure semiempirical calculations and available experimental and ab initio data. It is shown that, in many cases, the hybrid QM /MM potential behaves better than do related MNDO /M , AM 1, and PM 3 methods. As a case in point, the draw-back of AM 1 favoring bifurcated H-bonded structures over single ones is not presented in the combined AM 1/OPLS scheme. Possible ways of improvement of the combined QM /MM potential are discussed. © 1992 John Wiley & Sons, Inc.     

Synthesis and liquid crystal properties of dinuclear cyclopalladated 5-alkyl-2-(4'-alkoxyphenyl)pyrimidine and 3-(4'-alkoxyphenyl)-6-alkoxypyridazine complexes

The dinuclear cyclopalladated complexes [Pd(L₁ or L₂)(µ-X)]₂ (HL₁=5-alkyl-2-(4'-alkoxyphenyl)pyrimidine, HL₂=3-(4'-alkoxyphenyl)-6-alkoxypyridazine, X=Cl^-, CH₂ClCOO^-, CH₂BrCOO^-, CH₃CHBrCOO^-, CH₂BrCH₂COO^-, CH₃COO^-) have been synthesized and characterized; their mesogenic properities were determined by DSC and polarizing microscopy. The effect of the bulk and the polarity of the bridging ligands on their mesogenic properties is discussed. The effect of the length of the alkyl chains on the mesogenic properties of these organometallic complexes has also been investigated.     

Design and synthesis of porphyrins bearing rigid hydrogen bonding motifs: highly versatile building blocks for self-assembly of polymers and discrete arrays

Two aldehydes, 2,6-diacetamido-4-formylpyridine (7) and 1-butyl-6-formyluracil (11), are used to synthesize five pyridyl and four uracyl meso-subsituted porphyrins. With these complementary porphyrin building blocks, it is possible to build various types of multi-porphyrin supramolecules with different spatial relationships in predefined geometries. The formation and properties of self-complementary dimers and a closed tetrameric square are presented as a basis of comparison to the latter system in the solid state. An X-ray structure of 5,10-bis(4-tert-butylphenyl)-15,20-bis(3,5-diacetamido-4-pyridyl)porphyrin confirms its molecular structure and reveals a hydrogen-bonded supramolecular organization mediated by water molecules.