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Photoresponsive nanostructured materials are of great importance for photonic applications. Herein we report the design, synthesis, and liquid crystal (LC) self-assembly of two new series of photoresponsive hockey-stick LCs (HSLCs). The new HSLCs are azobenzene-based polycatenars derived from the 4-cyanoresorcinol bent-core unit. The long arm is a fork-like triple alkoxylated wing, while the short arm is terminated with a single variable alkoxy chain. The molecular self-assembly of these HSLCs is characterized using polarizing optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and electro optical measurements. In both series of LC materials differing in the chain volume at the crowded end, wide temperature ranges of lamellar Smectic A phases (up to 170 K) are observed beside achiral isotropic liquid phases (Iso1) for the shorter derivatives. On chain elongation helical self-assembly of the π-conjugated rods in networks occurs resulting in the formation of nanostructured bicontinuous cubic network phases with Ia3¯d space group (Cubbi/Ia3¯d), in most cases stable even around room temperatures on cooling. At the transition from SmA to Cubbi phases, an additional unknown three-dimensional (3D) phase is formed. A possible explanation for the disappearance of the triple network Cubbi phases with I23 symmetry (Cubbi[*]/I23) in these HSLCs is represented based on the phase behaviour of a new material having the central 4-cyanoresorcinol unit shifted to a terminal position of the rod-like core. Finally, the reversible trans–cis photoisomerization for some selected examples was investigated in chloroform solution. [ABSTRACT FROM AUTHOR]

Multiple mesophases, including the smectic A phase (Sm A), chiral nematic phase (N*), and blue phase (BP I), were seen in a series of non-symmetric bent mesogenic dimers containing a cholesteryl benzoate group. FTIR, 1H-NMR, DSC, POM, UV, and XRD were used to analyze the chemical structure and liquid crystal characteristics of the dimers. The phase transition occurred when the azobenzene structure was treated with UV light, changing the structure of the molecules. There is evidence that when the length of the terminal alkoxy chain is longer than the flexible spacer, it exhibits a smectic A phase as well as a chiral nematic phase; however, when the length of the flexible spacer is shorter than the length of the terminal alkoxy chain, it only exhibits a chiral nematic phase. [ABSTRACT FROM AUTHOR]

A new family of supramolecular liquid crystalline compounds with a calix[4]arene core and two linking groups appended on four sides, exhibiting a wide range of hexagonal columnar phases, has been synthesised and well characterised. The liquid crystal behaviour of the novel materials was studied by using polarising optical microscopy (POM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), and was further confirmed using high-temperature powder X-ray diffraction (XRD). An electrochemical study was carried out using cyclic voltammetry (CV) and the results were compared with theoretical values obtained from a DFT study. These compounds showed light sky-blue luminescence in solution and as a thin film under long-wavelength UV light. It was observed that all the prepared target compounds exhibited enantiotropic mesophases with good thermal stability. The structural and conformational characterisation of these new compounds was achieved using various spectroscopic techniques, including FT-IR, 1H NMR, 13C NMR and MALDI-TOF. The relationship between the structure and the mesomorphic behaviour of the compounds containing an ethyl bridge with linked ester groups (5a–5d) is discussed. This new class of supramolecular derivatives is promising, especially considering the emissive nature and stabilisation of their columnar hexagonal mesophases, and their high range of thermal stability. [ABSTRACT FROM AUTHOR]

A series of three triphenylene compounds – denoted 2,7-THTP-DiCnOH – bearing four hexyloxy ancillary chains and two variable-length alkoxy chains terminally functionalized with hydroxyl groups have been synthesized and characterized. The studied compounds exhibited thermotropic mesomorphism; the detailed nature of the mesophases was found to depend on the relative positions of the terminal functional groups relative to the crown formed by the ancillary chains. All the studied compounds were able to act as supramolecular gelators in a variety of alcohols; their organogelating ability has been rationalized in terms of physicochemical parameters like the dielectric constant, which allowed us to establish very precise predictive "solvent gelation windows" for each compound. Remarkably stable gels have been detected for 2,7-THTP-DiC6OH in methanol. As a proof of principle, we present the water sensing performance as a rapid method for the assessment of water content in alcohol samples based on the influence that the water content exerts on the gels' thermostability. [ABSTRACT FROM AUTHOR]

The enantiomer separation of a chiral Tröger's base analog and its use, as an optically active building block, in the construction of molecular superstructures are presented. Various strategies are illustrated here for the attachment of azo photoswitches to the Tröger's base scaffold without racemizing its stereogenic centers. The resulting optically active photoswitches introduced chirality, thermochromic, and phototunable properties to an achiral liquid crystal host. The doped mesophases reflected specific wavelengths of light owing to the formation of self-organized helical superstructures. These observations illustrate the potential use of the presented products as liquid crystal dopants. [ABSTRACT FROM AUTHOR]

Organoboron complexes are considered to be an important class of optically dynamic materials and because of their imperative properties, they have been unceasingly studied in a wide range of scientific areas. In this context, a new family of D–A–D′ architectured boron difluoride complexes FB1–4 derived from arylhydrazones HZ1–4 has been synthesized and characterized. The work also deliberates detailed studies on their thermal, self-assembling and optoelectronic properties with respect to structural modifications. The systematic studies reveal that the new arylhydrazone ligands and their BF2 complexes exhibit a prospective columnar mesomorphism with different 2D lattice geometries at room temperature, owing to their critical structural features. Interestingly, an unusual morphological cross-over from a columnar hexagonal to rectangular mesophase has been confirmed in one of the investigated pseudo-discoidal boron complexes, FB4. The optoelectronic studies showcased their ICT dominating dye properties. Finally, the experimental results have been consciously correlated with quantum chemical simulations. [ABSTRACT FROM AUTHOR]

Thermotropic liquid crystals with π-conjugated cores are increasingly witnessed due to their promising optoelectronic and optophotonic properties. As π-conjugated mesogens are often realized by direct linking of the rings of the core, the mesophase transitions are usually modulated by inserting the required alkyl/alkoxy chains either at a terminal or lateral location. In this work, five mesogens in which thiophene and two phenyl rings are common in the core unit with terminal alkyl/alkoxy chains are investigated to probe the influence of (a) a terminal alkyl chain on the mesophase characteristics, (b) the linking units on the mesophase range and (c) the disparity of thiophene orientational constraints. The mesophase properties reveal that whenever the alkyl chain is located at one end of the molecule, polymesomorphism is observed. The XRD studies reveal layer ordering typical of smectic mesophases with lower temperature and higher order phases, namely SmB and CrE phases. A detailed 13C NMR study of the mesogens in the liquid crystalline phase indicates that the order parameters are governed by the nature of the substitution of thiophene and its linkage with two phenyl rings. Importantly, the 13C NMR data of the terminal chains in the liquid crystalline phase are compared with the recently reported thiophene mesogen in which the n-hexyl chain is located at the lateral position and completely different orientation characteristics were found for the terminal versus lateral chains. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of different lateral substituents at different locations of dimers as well as the direction of ester linkages on the mesogenic properties, several new homologous series of dimeric compounds are synthesised. Here, two rod-like non-mesogenic laterally substituted azo moieties are connected to each other by an alkylene spacer through ester linkages. In all these dimers, the end alkoxy chain length is kept constant and the length of the spacer chain is varied. An odd–even effect of methylene groups in the spacer chain is observed in addition to a clear effect of lateral substituents at different positions and the direction of ester linkages on the mesomorphic properties. These dimers exhibit nematic and smectic mesophases. The X-ray diffraction studies revealed that the nematic phases are composed of skewed smectic nanoclusters (NcybC) irrespective of whether a smectic phase exists below the nematic phase or not. We did not observe any bent-core phases in these dimers. They are photo-switching both in solution and in their nematic mesophases. We observed that the photo-induced effect is more pronounced in the case of dimers with an odd-spacer when compared to those with an even-spacer. The gelation properties of these dimers are also investigated and a comparison of the liquid crystalline and gelation properties of these dimers has been made with reported similar but laterally unsubstituted dimers. [ABSTRACT FROM AUTHOR]

Two new regioisomeric star-shaped tris(N-salicylideneaniline)s are synthesized and characterized. The arms of these star-shaped mesogens differ from each other with respect to the substitution on the 3,5-positions of the central 1,2,4-oxadiazole moieties. The unsymmetrical nature of substitution leads to a change in the distribution of electron density, which will have an effect on the type of columnar self-assembly. One of these molecules stabilizes the columnar hexagonal phase, while the other one stabilizes the columnar rectangular phase. The columnar rectangular phase, which requires enhanced intermolecular interactions, is observed in the case of the star-shaped molecule, where the trialkoxy phenyl group is connected at the 5-position of the heterocycle, whereas the columnar hexagonal phase is observed in the case of the star-shaped molecule, where the trialkoxy phenyl group is connected at the 3-position of the heterocycle. These compounds showed reduced melting points, clearing points and an enhanced mesophase range with respect to their symmetric counterpart (1,3,4-oxadiazole derivative) reported earlier. All the molecules exhibited green light emission in solution, with good quantum yield. The emission of 1,2,4-oxadiazole derivatives was considerably red-shifted in comparison to those of 1,3,4-oxadiazole derivatives. This study emphasizes how a minor change in the molecular structure brings about a beneficial change in the self-assembly characteristics of star-shaped molecules. [ABSTRACT FROM AUTHOR]

A simple but novel class of hydrogen bonding liquid crystalline benzoic acids with alkylthio (or alkylsulfanyl; SR) groups was established. In general, although it is difficult for laterally non-substituted rod-like molecules with an alkylthio group to form some mesophases, the present molecules exclusively form a nematic (N) regime, owing to spontaneous carboxylic dimerization. It was found that the number of carbons in the alkylthio groups strongly correlated with transition temperatures as well as nematogenic stability: odd–even effects. Even-members displayed wider monotropic and enantiotropic N phases, despite the fact that almost all odd-members showed either none or only monotropic-narrower ones. Interestingly, their thermal transition temperatures were lower compared to those for alkoxy (OR) analogues, on account of the small angle (or large bend) of the C–S–C bond as well as the low electron density on their aromatic ring due to the weak electron donor properties of alkylthio groups. Additionally, in-depth wide-angle X-ray diffraction measurements revealed that an alkylthio analogue exhibited significantly enhanced smectic clusters formed in the N regime (or Ncyb phase) as well as the cluster type close to smectic (Sm) A, in comparison with an alkoxy analogue exhibiting a clear SmC-type cluster. The results indicate that a robust S…S intermolecular interaction for an alkylthio group into a mesogen affects the kind of smectic cluster in the Ncyb phase. [ABSTRACT FROM AUTHOR]

Several new square planar platinum(ii) complexes based on modified 2-phenylpyridine derivatives as the main ligand and picolinic acid as the auxiliary ligand were synthesized and their photophysical properties, and mechanochromic and liquid crystalline behavior were investigated. It is found that only the Pt–L1 complexes, in which one flexible long chain is attached to each end of 2-phenylpyridine, display monotropic smectic liquid crystalline behavior. Moreover, mechanochromism has been observed by grinding the solid complexes. It seems that the liquid crystalline and mechanochromic properties of these complexes are relative to the number of flexible alkoxy chains in the cyclometalated ligand. [ABSTRACT FROM AUTHOR]

We report the synthesis and mesophase characterization of a series of novel di- and tetra-aryl acenequinones. Diphenyl-acenequinones 1 and 2 exhibit monotropic mesophases while tetra-aryl acenequinones 4 and 5 exhibit stable columnar hexagonal mesophases. Compound 4 exhibits a more stable columnar mesophase than 5, consistent with a packing motif where molecules are stacked in perpendicular arrangement. [ABSTRACT FROM AUTHOR]

Sustainable plant-derived N-oleyl-1,3-diaminopropane surfactant micelles cross-linked by divinylbenzene (DVB) have been intercalated in the pores of mesostructured silica and the resulting functionalized mesophases were used to immobilize heavy metal ions through complexation by the diamine head groups. Two methods were used to form the composite surfactant–silica compositions. In the “pre-assembly” approach, the unsaturated amine micelles were first cross-linked in aqueous solution and subsequently used as a structure-directing agent to form the composite silica–polymeric amine mesophase. In the second “post-assembly” approach, the unsaturated amine micelles were used to template the silica mesophase and then cross-linked in situ with DVB within the pores of the composite mesophase. The accessibility of the amine functional groups in the mesophases prepared by both assembly methods was demonstrated through the uptake of Cu(ii) and Pb(ii) ions from aqueous solution. [ABSTRACT FROM AUTHOR]

Oil-swollen hexagonal mesophases resulting from the surfactant mediated self-assembly of a quaternary mixture of water, surfactant, co-surfactant, and oil, are versatile templates to synthesize anisotropic nanomaterials. Poly(diphenylbutadyine) (PDPB) polymer nanofibrous network structures were produced in the oil tubes of the mesophases by photo-induced radical polymerization using a chemical initiator or by gamma irradiation. The diameter of the nanofibers can be varied from 5 to 25 nm in a controlled fashion, and is directly determined by the diameter of the oil tube of the doped mesophases, proving thus a direct templating effect of the mesophase. The nanoIR technique allows chemical characterization and identification of the polymer nanostructures simultaneously with morphological characterization. Cyclic voltammetry has been used as an effective approach to evaluate both the energy level of the highest occupied molecular orbital (HOMO) as well as the energy of the lowest unoccupied molecular orbital (LUMO) and the band gap of the PDPB. The conductivity of the PDPB nanostructures obtained by gamma irradiation was estimated to be 10−1 S cm−1, which is higher than the conductivity of PDPB nanostructures previously reported in the literature. The soft template approach allows size tunable synthesis of anisotropic polymer structures with morphological homogeneity at the nanoscale with high conductivity, thus it appears to be an attractive opportunity for electronic device applications. [ABSTRACT FROM AUTHOR]

The synthesis of the corrole-based liquid crystal phase CorLC is described together with its full characterization using a combination of Polarised Optical Microscopy (POM), ThermoGravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) measurements and Small-Angle X-Ray Diffraction (SA-XRD), which shows that CorLC has a hexagonal columnar organization at room temperature. The light absorption and hole-transport properties of the mesophase CorLC are compared with those featured by assemblies of its parent meso-triaryl (Cor1) and per-aryl (Cor2) derivatives. J-Aggregates are replaced by H-aggregates when the intermolecular distance is increased by a higher peripheral steric hindrance producing lower hole-transport mobilities. [ABSTRACT FROM AUTHOR]

Herein, we report on the synthesis, characterization, liquid crystalline behavior and chirooptical properties of five (R)-4-{[(4-(octan-2-yloxy)phenyl)imino]methyl}phenyl 4-(n-alkoxy)benzoates and their enantiomers, namely, (S)-4-{[(4-(octan-2-yloxy)phenyl)imino]methyl}phenyl 4-(n-alkoxy)benzoates. These three-ring rod-like mesogens were prepared by acid catalyzed condensation of (R)-/(S)-4-(octan-2-yloxy)anilines with 4-formylphenyl 4-(n-alkoxy)benzoates. Thus, each pair of enantiomers comprises (R)-2-octyloxy and (S)-2-octyloxy chiral tails. In order to understand the structure–property correlations, the length of the paraffinic chain incorporated at the other end has been varied from n-octyloxy to n-dodecyloxy. A detailed study carried out by means of several complimentary techniques reveals the stabilization of liquid crystal phases that hold great promise in applied sciences especially in various device applications. In particular, the occurrence of mesophases such as the blue phase-I/II (BPI or BPII) and chiral nematic (N*) and chiral smectic C (SmC*) phases has been evidenced unequivocally with the help of polarizing microscopy, differential scanning calorimetry, X-ray diffraction and electrical switching. Besides, the occurrence of an unknown, metastable smectic (SmX) phase below the SmC* phase has been noted. This study shows that the length of the terminal tail seems to determine the thermal range of the SmC* phase. The enantiotropic SmC* phase exhibiting ferroelectric switching behavior occurs over 60 °C thermal range; notably, the spontaneous polarization (Ps) value crosses over 100 nC cm−2. The photophysical properties and chirooptical behavior of the mesogens have been studied with the aid of UV-vis absorption and circular dichroism (CD) spectroscopic methods, respectively; the latter technique has been especially used to ascertain the twist sense of the N* and SmC* phases formed by a pair of enantiomers. The reversal of the helix-sense (from right to left and vice versa) during the N*–SmC* phase transition has been observed for the first time. [ABSTRACT FROM AUTHOR]

Three novel gallic-perylene-gallic trimers 7, 8 and 9 were synthesized by reacting gallic amino derivatives 3, 4 or 6 with perylene tetracarboxylic anhydride in yields of 75%, 78% and 80%, respectively. Compounds 7 and 8 with soft bridging chains exhibit columnar mesophase at room temperature, but compound 9 with a rigid bridging chain exhibits no mesophase. [ABSTRACT FROM AUTHOR]

We describe a single step preparation of nanostructures of poly(3,4-ethylenedioxythiophene), PEDOT, in the hydrophobic domains of cationic surfactant-based hexagonal mesophases via chemical oxidative polymerization of EDOT monomers using FeCl3 as an oxidizing agent. After polymerization, the hexagonal structure of the mesophases is preserved as demonstrated by polarized light microscopy and X-ray scattering measurements. After extraction from mesophases, the chemical structure of PEDOT is confirmed by Fourier transform infrared spectroscopy. Moreover, PEDOT morphology is checked by transmission and scanning electron microscopies. PEDOT nanostructures with spindle-like or vesicle-like shapes are obtained depending on the experimental conditions. In the original method, high resolution atomic force microscopy, coupled with infrared nanospectroscopy, is used to probe the local chemical composition of PEDOT nanostructures. Finally, the as-prepared PEDOT polymers are characterized by both good thermal stability up to 200 °C and a relatively high conductivity value up to 0.4 S cm−1 as determined by thermogravimetric analysis and four probe measurements respectively. [ABSTRACT FROM AUTHOR]

The first bent-core liquid crystal materials with a photo-active azo linkage exhibiting the B7 mesophase are reported. The lower homologues of the bent-core compounds display the B1 phase and higher homologues show the B7 mesophase. The mesomorphic properties were characterized using polarized optical microscopy, differential scanning calorimetry and X-ray diffraction. The B7 phase of these materials establishes ferroelectric switching characteristics with anticlinic organization (SmCAPF) of the molecules in the layers. The bent-core molecules with an azo linkage are important for photoisomerization studies, which indicate trans to cis isomerization at 30 s, whereas the reverse processes take place over 40 s in chloroform. [ABSTRACT FROM AUTHOR]