Spectroscopic study of liquid crystalline N-[4-(4-n-alkoxybenzoyloxy)2-hydroxybenzylidene]hydroxyanilines

New homologous series of N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]hydroxyanilines were synthesized. All 4-hydroxyaniline derivatives exhibited a nematic phase, while 3-hydroxyaniline and 2-hydroxyaniline derivatives exhibited only a nematic phase as the terminal alkoxy group was lengthened. Infrared spectra suggest that the 4-hydroxyaniline derivatives form intermolecular hydrogen bonding of the single bridge type, while the 3-hydroxy and 2-hydroxy derivatives form the polymer type. The Raman band at around 1360 cm^-1 exhibited large differences in intensity among these derivatives. This can be explained by the effect of intermolecular or hydrogen bonding molecular conformation.     

Effects of benzoyl group substituents on the mesomorphic properties of 5-alkoxy-2-benzoylaminotropones

Three types of 5-alkoxy-2-benzoylaminotropones, containing an electron-donating group and seven types of derivatives with electron-withdrawing groups on the benzoyl group, were prepared in order to study the thermal ranges of the mesophases exhibited. The troponoid amides had higher transition temperatures than the corresponding troponoid esters and benzenoid amides. From the ¹H NMR spectroscopic measurements and X-ray crystallographic analysis of 5-butoxy-2-(4-methoxybenzoylamino)tropone, it was observed that the benzoyl carbonyl group faced to the H-3 of the tropone ring to form an intramolecular hydrogen bond between the tropone carbonyl and the amide NH groups. The intramolecular hydrogen bonding of the troponoid amides made the molecules flat, inducing strong π-π intermolecular interactions between head-to-tail dimers and so reduced the possibility of intermolecular hydrogen bonding between the NH group and the carbonyl group of neighbouring molecules so decreasing melting points. Electron-donating groups enhanced the appearance of nematic phases while electron-withdrawing groups promoted smectic A phases.     

Effects of benzoyl group substituents on the mesomorphic properties of 5-alkoxy-2-benzoylaminotropones

Three types of 5-alkoxy-2-benzoylaminotropones, containing an electron-donating group and seven types of derivatives with electron-withdrawing groups on the benzoyl group, were prepared in order to study the thermal ranges of the mesophases exhibited. The troponoid amides had higher transition temperatures than the corresponding troponoid esters and benzenoid amides. From the ¹H NMR spectroscopic measurements and X-ray crystallographic analysis of 5-butoxy-2-(4-methoxybenzoylamino)tropone, it was observed that the benzoyl carbonyl group faced to the H-3 of the tropone ring to form an intramolecular hydrogen bond between the tropone carbonyl and the amide NH groups. The intramolecular hydrogen bonding of the troponoid amides made the molecules flat, inducing strong π–π intermolecular interactions between head-to-tail dimers and so reduced the possibility of intermolecular hydrogen bonding between the NH group and the carbonyl group of neighbouring molecules so decreasing melting points. Electron-donating groups enhanced the appearance of nematic phases while electron-withdrawing groups promoted smectic A phases.     

含甲氧基偶氮苯基元的苯甲酸衍生物的合成与液晶性研究

合成和表征了新型的含有甲氧基偶氮苯液晶基元的3,4,5-三取代苯甲酸衍生物Dn, 研究了结构对其相行为的影响. 结果表明, 在Dn中, 羰基(C=O)和羟基(OH)之间的氢键相互作用存在于结晶态、液晶态和各向同性状态, 在各向同性态时氢键较弱. 通过对其分子结构的调控, 有效地抑制了微相分离和强的分子间的相互作用, 得到了具有单向向列型液晶行为的3,4,5-三取代的苯甲酸衍生物.     

Self-assembled discotic nematic liquid crystals formed by simple hydrogen bonding between phenol and pyridine moieties

New discotic nematic liquid crystals have been prepared through intermolecular hydrogen bonding between the core of 1,3,5-trihydroxybenzene (phloroglucinol, PG) or 1,3,5-tris(4-hydroxyphenyl)benzene (THPB) and the peripheral molecules of stilbazole derivatives. The various nematic phases formed by new hydrogen bonding building blocks were investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The first discotic complexes of PG and trans-4-alkoxy-4′-stilbazoles exhibited nematic columnar (N_C) and hexagonal columnar phases depending on the length of alkyl chains, which were considered as the basic discotic structure. Several structural variations on the building blocks were attempted to examine their effects on the liquid crystalline properties of discotic complexes. The nematic lateral phase (N_L) with enhanced intercolumnar order was observed for the complexes of PG and trans-4-cyanoalkoxy-4′ stilbazoles due probably to the strong dipole interactions between cyano groups at the end of alkoxy chains. By introducing the nonlinear structure in three arms of supramolecular discotic mesogen, a discotic nematic phase (N_D) was observed for the complex of THPB and trans-4-octyloxy-4 -stilbazole. The single hydrogen bonding between phenol and pyridine moieties in this study provides a simple and effective method for preparing the rarely found discotic nematic liquid crystals.     

新型低聚噻吩衍生物的设计、合成及其液晶性能的研究

设计、合成了一系列新型低聚噻吩衍生物N,N’-双烷烃基-5,5’-二溴基-2 ,2’：5’,2’-三噻吩-4,4’-二酰胺[N,N’-dialkyl-5,5’-dibromo-2,2’:5 ’,2’-terthiophene-4,4’-dicarboxamide](DNCnDBr3T,n=5,8,6,18)。示差扫描 量热法（DSC）测定的结果及偏光光学显微镜观察的结果显示,DNC18DBr3T, DNC16DBr3T,DNC8DBr3T具有近晶A形液晶性质,DNC5DBr3T不具有液晶性质。为了探 讨分子间氢链对液晶形成的影响,设计、合成了新型低聚噻衍生物4,4“-双烷烃 酯-5,5“-二溴基-2,2’:5’,2’-三噻吩[4,4’-bis(alkyloxycarbonyl)-5,5’ -dibromo-2,2’:5’,2’-terthiophene](DOCnDBr3T,n=5,8,16,18).测定和观察的 结果发现,DOCnDBr3T(n=5,8,16,18）不具有液晶的结果。这个结果表明,酰胺基 的存在于液晶的形成起着重要的作用。测定DNC18DBr3T在结晶状态和液晶状态下的 红外光谱,进一步证实了部分分子间氢键对于液晶的形成起着重要的作用。     

The substituent effect on mesomorphic properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy)benzoates and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates

The thermal properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy) benzo-ates (1) and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates (2) have been examined, where R = hydrogen, halogens, alkyl and alkoxy groups. The derivatives of compound 1 incorporating hydrogen, halogens, methoxy and nitro groups show a smectic A phase having a bilayer arrangement, and the others with a long alkoxy group show the S_A phase with the monolayer arrangement. The derivatives of compound 2 incorporating halogens, and the nitro group show the S_A phase with the monolayer arrangement. The alkoxy derivatives show a smectic C phase as well as the nematic phase. The nitro group at the lateral position tends to increase the ratio of the S_A-N transition temperature to the N-I. The effect of the nitro group on the smectic properties has been discussed in terms of the structural and electrostatic nature of the nitro group.     

Structural and spectral studies of a 1-N(4)-substituted thiosemicarbazone derived from 2-hydroxy-1,4-naphthaquinone

2-Hydroxy-1,4-naphthaquinone reacted with N(4)-ethylthiosemicarbazide in basic solution forms the 1-thiosemicarbazone. The crystal structure shows that the 2-hydroxy hydrogen is shifted to the remaining quinone oxygen resulting in the formation of a dimer due to intermolecular hydrogen bonding from each hydroxy group to the other molecule's quinone oxygen. Intramolecular hydrogen bonding occurs between the amide NH and the imine thiosemicarbazone moiety, as well as between the hydrazinic NH and the quinone oxygen. This new compound's IR, UV and ¹H NMR spectra are included.     

Synthesis and variable-temperature FTIR study of five chiral liquid crystals induced by intermolecular hydrogen bonding

Five new chiral liquid crystal systems induced by intermolecular hydrogen bonding between 4-[(s)-2-chloro-3-methyl]butyroyloxy-4'-stilbazole (MBSB, proton acceptor) and 4-alkoxybenzoic acids (nBA, proton donors) were prepared. Their liquid crystalline properties were investigated by DSC and polarized optical microscopy. Chiral nematic and chiral smectic phases were observed, and the thermal stability of one complex was studied through temperature dependent infrared spectroscopy.     

Phase transitions of 6-(4-n-alkoxybenzoyloxy)-flavones and 3-cyano-7-(4-n-alkoxybenzoyloxy)-coumarins

Phase transitions of 6-(4-n-alkoxybenzoyloxy)-flavones (ABF) and 3-cyano-7-(4-n-alkoxybenzoyloxy)-coumarins (CABC) were studied using D.S.C. and polarized microscopy. ABF series showed a nematic phase which has an excellent thermal stability, whereas CABC series exhibited a smectic A phase in the longer 4-n-alkoxybenzoyloxy ones than 4-n-hexyloxybenzoyloxy. This difference in the mesogenicity was discussed from the structure and polarity of flavone and coumarin skeletons which may be associated with an intermolecular interaction in the mesophase.     

Influence of hydrogen bonding on phase abundance in ferroelectric liquid crystals

The synthesis and characterization of five hydrogen-bonded ferroelectric liquid crystal complexes (HBFLCs) prepared from mesogenic p-n-alkoxy benzoic acids and non-mesogenic propionic/butyric acids with different chiral centres are reported. Complementary intermolecular hydrogen bonding is confirmed through IR study. HBFLCs are found to exhibit chiral nematic (N*), smectic C* (SmC*) and smectic G* (monotropic) phases in their cooling profiles during polarizing thermal microscopy and differential scanning calorimetry. Phase coexistence regions are observed above the IN* transition. The chiral nematic to smectic C* transition is found to be of first order. The temperature variation of spontaneous polarization exhibited by these HBFLC complexes in their SmC* phase is presented. The effect of non-covalent interaction imparted by the soft hydrogen bonding in these LC complexes on enhanced or induced thermal stability of tilted LC phases is discussed.     

Rebek imides and their adenine complexes: preferences for Hoogsteen binding in the solid state and in solution

Rebek imides (3), formed from Kemp's triacid, were developed in the mid-1980's as model receptors for adenine derivatives. We report here the first account of their hydrogen-bonding preferences upon binding 9-ethyladenine (1a) in the solid state. Structural analysis begins with simple imides 3a-e that form discrete dimers, while bis-imide 4 forms ribbon-like structures in the crystalline phase. The hydrogen-bonding interface within each of the representative assemblies features short intermolecular N(3)imide...O(8*)imide* distances (ca. 2.95 A), indicative of two-point hydrogen bonding. Imides 3f-h could be co-crystallized with 1a; single-crystal X-ray analysis of the resulting complexes reveals hydrogen-bonding geometries nearly identical to those observed in nucleobase complexes of adenine and pyrimidine derivatives. Imides 3f and 3g form 2:1 ternary assemblies with 1a; the complex of the former, (3f)2 x 1a, displays both Watson-Crick- and Hoogsteen-type hydrogen bonding, whereas the complex of the latter, (3g)2 x 1a, shows the Hoogsteen motif and imide hydrogen bonding to N(3) of the purine base (N(3)adenine...N(3')imide = 3.07(1) A). Imide 3h forms a 1:1 complex with 1a (3h x 1a x CHCl3) and displays Hoogsteen binding exclusively. All of the 3 x 1a assemblies show C(adenine)...O(imide) distances (3.38-3.75 A) that are consistent with C-H...O hydrogen bonding. Base-pairing preferences for the Rebek imides are further explored in solution by 1H NMR one-dimensional NOE experiments and by computational means; in all cases the Hoogsteen motif is modestly favored relative to its Watson-Crick counterpart.     

Theoretical investigations on chalcogen-chalcogen interactions: what makes these nonbonded interactions bonding?

To understand the intermolecular interactions between chalcogen centers (O, S, Se, Te), quantum chemical calculations on pairs of model systems were carried out. For the oxygen derivatives, one of the components of the supermolecules consists of dimethyl ether, while the second component is either dimethyl ether (1) or ethynyl methyl ether (2) or methyl cyanate (3). The model calculations were also extended to the sulfur (4-6), selenium (7-9), and tellurium congeners (10-12). The MP2/SDB-cc-pVTZ, 6-311G level of theory was used to derive the geometrical parameters and the global energies of the model systems. A detailed analysis based on symmetry adapted perturbation theory (SAPT) reveals that induction and dispersion forces contribute to the bonding in each case. For 1-3 the electrostatic energy also contributes to the intermolecular bonding, but not for 4-12. The NBO analysis reveals that the interaction in the dimers 1-3 is mainly due to weak hydrogen bonding between methyl groups and chalcogen centers. Similar hydrogen bonding is also found in the case of 4 and to a lesser extent in 5 and 7. For the aggregates with heavier centers the chalcogen-chalcogen interaction dominates, and hydrogen bonding only plays a minor role. Electron-withdrawing groups on the chalcogen centers increase the interaction energy and reduce the intermolecular distance dramatically. The one-electron picture of an interaction between the lone pair of the donor and the chalcogen carbon sigma orbital allows a qualitatively correct reproduction of the observed trend.     

The substituent effect on mesomorphic properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy)benzoates and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates

Abstract

The thermal properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy) benzo-ates (1) and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates (2) have been examined, where R = hydrogen, halogens, alkyl and alkoxy groups. The derivatives of compound 1 incorporating hydrogen, halogens, methoxy and nitro groups show a smectic A phase having a bilayer arrangement, and the others with a long alkoxy group show the S_A phase with the monolayer arrangement. The derivatives of compound 2 incorporating halogens, and the nitro group show the S_A phase with the monolayer arrangement. The alkoxy derivatives show a smectic C phase as well as the nematic phase. The nitro group at the lateral position tends to increase the ratio of the S_A-N transition temperature to the N-I. The effect of the nitro group on the smectic properties has been discussed in terms of the structural and electrostatic nature of the nitro group.     

Induction of mesomorphism in mixtures of poly[4-(3-methacryloylpropyl)pyridine] with partially fluorinated derivatives of benzoic acid

LC complexes of nonmesomorphic poly[4-(3-methacryloylpropyl)pyridine] with partially fluorinated derivatives of benzoic acid have been prepared via intermolecular hydrogen bonding between complex components. The induction of mesomorphic state has been observed for both mesomorphic and nonmesomorphic acids. It has been shown that the type of a mesophase manifested by the complexes varies from layered to columnar and cubic depending on the number of substituents in a low-molecular-mass component.     

Smectic A liquid crystals from dihydrazide derivatives with lateral intermolecular hydrogen bonding

Six dissymmetrical dihydrazide derivatives, N-(4-alkoxybenzoyl)-N′-(4′-nitrobenzoyl) hydrazine (Cn-NO₂) and N-(4-alkoxybenzoyl)-N′-(4′-biphenyl carbonyl) hydrazine (Cn-Ph), were synthesized and investigated by means of differential scanning calorimetry, polarized optical microscopy and wide angle X-ray diffraction. The compounds exhibit smectic A₁ phase. Based on the results of ¹H NMR and variable temperature FT-IR spectroscopy, lateral intermolecular hydrogen bonding between -CO and -N-H groups was proposed and the effect of hydrogen bonding on the phase transitions was discussed. It was concluded that the combination of lateral intermolecular hydrogen bonding and microphase segregation stabilized the smectic A phase.     

Three‐Ring‐Based Room‐Temperature Bent‐Core Nematic Compounds: Synthesis and Characterization

We report the synthesis and characterization of a new class of achiral three‐ring bent‐core compounds with an amide and ester linkage at the molecular bend, which are shown to exhibit nematic/phases in wide temperature ranges around room temperature (RT) and undulated SmC phases below RT. In contrast to previous studies, the compounds reported in this Communication show a true RT nematic phase with fluid physical appearance. They show strong photoluminescence in the mesophase and are found to display a one‐dimensional array of intermolecular hydrogen bonding. Furthermore, the nematic phases exhibited by these compounds show a good homeotropic alignment that can be exploited in applications such as optics and sensing. Considering the scarcity of bent‐core materials exhibiting an RT nematic mesophase, this new class of materials is promising.     

Investigation into the GC separation of enantiomers on a trifluoroacetylated cyclodextrin. Part II: Effect of derivatization on stereoselectivity towards alcohols

Two acyl and three fluoroacyl derivatives of 32 chiral alcohols have been chromatographed on a GC column coated with octakis(2,6-di-O-n-pentyl-3-O-trifluoroacetyl)- γ-cyclodextrin. Significant differences were observed between the stereoselectivity obtained for the derivatives and that for the underivatized alcohols. Of the derivatives, only the fluoroacylated compounds were separated into enantiomers. Derivatization with fluoroacyl groups reversed the elution order for at least some of the analytes. Stereoselectivity towards simple 2- and 3-hydroxy alkanes and their fluoroacyl derivatives was highest for those alcohols with a four-carbon chain attached to the stereogenic center. For longer-chain fluoroacyl derivative groups stereoselectivity was higher for the 2- and 3-hydroxy alkanes. Differences in stereoselectivity towards alcohols with a methyl-branched alkane chain and their fluoroacyl derivatives was related to the distance between the methyl group and the hydroxyl or fluoroacyl groups. Different degrees of saturation in the carbon chain resulted in differences in stereoselectivity. Thermodynamic data calculated for a number of analytes suggest that the alcohols and trifluoroacetate derivatives are interacting with the stationary phase by similar mechanisms. The stereospecific interaction appears to have a hydrogen bonding or dipole–dipole contribution and some form of steric component, depending upon the shape and/or size of the solute.     

The Balance between Hydrogen Bonds,Halogen Bonds,and Chalcogen Bonds in the Crystal Structures of a Series of 1,3,4-Chalcogenadiazoles

In order to explore how specific atom-to-atom replacements change the electrostatic potentials on 1,3,4-chalcogenadiazole derivatives, and to deliberately alter the balance between intermolecular interactions, four target molecules were synthesized and characterized. DFT calculations indicated that the atom-to-atom substitution of Br with I, and S with Se enhanced the σ-hole potentials, thus increasing the structure directing ability of halogen bonds and chalcogen bonds as compared to intermolecular hydrogen bonding. The delicate balance between these intermolecular forces was further underlined by the formation of two polymorphs of 5-(4-iodophenyl)-1,3,4-thiadiazol-2-amine; Form I displayed all three interactions while Form II only showed hydrogen and chalcogen bonding. The results emphasize that the deliberate alterations of the electrostatic potential on polarizable atoms can cause specific and deliberate changes to the main synthons and subsequent assemblies in the structures of this family of compounds.     

Influence of hydrogen bonding on phase abundance in ferroelectric liquid crystals

The synthesis and characterization of five hydrogen-bonded ferroelectric liquid crystal complexes (HBFLCs) prepared from mesogenic p-n-alkoxy benzoic acids and non-mesogenic propionic/butyric acids with different chiral centres are reported. Complementary intermolecular hydrogen bonding is confirmed through IR study. HBFLCs are found to exhibit chiral nematic (N*), smectic C* (SmC*) and smectic G* (monotropic) phases in their cooling profiles during polarizing thermal microscopy and differential scanning calorimetry. Phase coexistence regions are observed above the IN* transition. The chiral nematic to smectic C* transition is found to be of first order. The temperature variation of spontaneous polarization exhibited by these HBFLC complexes in their SmC* phase is presented. The effect of non-covalent interaction imparted by the soft hydrogen bonding in these LC complexes on enhanced or induced thermal stability of tilted LC phases is discussed.