RESUMEN
Herein, we report the synthesis and self-assembly of a new class of amphiphilic azo dyes derived from a plant-based phenol, cardanol. Analysis of the self-assembly of these new azo derivatives was intriguing, and they exhibit some unique nanostructures, such as bicelles and microgel-like structures, and smectic-type thermotropic mesophases.
RESUMEN
The first examples of deep-red/near-infrared (NIR) photoluminescent, (n,π-conjugated) discotics, namely, C 3h -tris(keto-hydrazone)s, which are the tautomers of tris(azo-enol)s, have been synthesized via a facile one-step triple azo-coupling and characterized. The n,π-resonance-assisted intramolecular H-bonding, rendering planarity and shape persistence to the central core, facilitates their self-assembly into either a hexagonal columnar (Colh) phase (p6mm lattice) or a columnar rectangular (Colr) phase (p2mm lattice), over an extended thermal range including room temperature, fluorescing in the deep-red/NIR-I region. The low band gap with deep-red/NIR emission makes them ideal candidates for NIR-organic light-emitting diodes (OLEDs) and bioimaging.
RESUMEN
The chiral ferroelectric smectic C (SmC*) phase, characterized by a helical superstructure, has been well exploited in developing high-resolution microdisplays that have been effectively employed in the fabrication of a wide varieties of portable devices. Although, an overwhelming number of optically active (chiral) liquid crystals (LCs) exhibiting a SmC* phase have been designed and synthesized, the search for new systems continues so as to realize mesogens capable of meeting technical necessities and specifications for their end-use. In continuation of our research work in this direction, herein we report the design, synthesis, and thermal behavior of twenty new optically active, three-ring calamitic LCs belonging to four series. The first two series comprise five pairs of enantiomeric Schiff bases whereas the other two series are composed of five pairs of enantiomeric salicylaldimines. In each pair of optical isomers, the configuration of a chiral center in one stereoisomer is opposite to that of the analogous center in the other isomer as they are derived from (3 S)-3,7-dimethyloctyloxy and (3 R)-3,7-dimethyloctyloxy tails. To probe the structure-property correlations in each series, the length of the n-alkoxy tail situated at the other end of the mesogens has been varied from n-octyloxy to n-dodecyloxy. The measurement of optical activity of these chiral mesogens was carried out by recording their specific rotations. As expected, enantiomers rotate plane polarized light in the opposite direction but by the same magnitude. The thermal behavior of the compounds was established by using a combination of optical polarizing microscopy, differential scanning calorimetry, and powder X-ray diffraction. These complementary techniques demonstrate the existence of the expected, thermodynamically stable, chiral smectic C (SmC*) LC phase besides blue phaseâ I/II (BPI or BPII) and chiral nematic (N*) phase. However, as noted in our previous analogous study, the vast majority of the Schiff bases show an additional metastable, unfamiliar smectic (SmX) phase just below the SmC* phase. Notably, the SmC* phase persists over the temperature range ≈80-115 °C. Two mesogens chosen each from Schiff bases and salicylaldimines were investigated for their electrical switching behavior. The study reveals the ferroelectric switching characteristics of the SmC* phase featuring the spontaneous polarization (PS ) in the range 69-96â nC cm-2 . The helical twist sense of the SmC* phase as well as the N* phase formed by a pair of enantiomeric Schiff bases and salicylaldimines has been established with the help of circular dichroism (CD) spectroscopic technique. As expected, the SmC* and the N* phase of a pair of enantiomers showed mirror image CD signals. Most importantly, the reversal of helical handedness from left to right and vice versa has been evidenced during the N* to SmC* phase transition, implying that the screw sense of the helical array of the N* phase and the SmC* phase of an enantiomer is opposite.
RESUMEN
Three new heteroatom bay-annulated perylene bisimides (PBIs) have been synthesized by microwave-assisted synthesis in excellent yield. N-annulated and S-annulated perylene bisimides exhibited columnar hexagonal phase, whereas Se-annulated perylene bisimide exhibited low temperature columnar oblique phase in addition to the high temperature columnar hexagonal phase. The cup shaped bay-annulated PBIs pack into columns with enhanced intermolecular interactions. In comparison to PBI, these molecules exhibited lower melting and clearing temperature, with good solubility. A small red shift in the absorption was seen in the case of N-annulated PBI, whereas S- and Se-annulated PBIs exhibited blue-shifted absorption spectra. Bay-annulation increased the HOMO and LUMO levels of the N-annulated perylene bisimide, whereas a slight increase in the LUMO level and a decrease in the HOMO levels were observed in the case of S- and Se-annulated perylene bisimides, in comparison to the simple perylene bisimide. The band gaps of PBI and PBI-N were almost same, whereas an increase in the band gaps were observed in the case of S- and Se-annulated PBIs. The tendency to freeze in the ordered glassy columnar phase for PBI-N and PBI-S will help to overcome the charge traps due to crystallization, which are detrimental to one-dimensional charge carrier mobility. These solution processable electron deficient columnar semiconductors possessing good thermal stability may form an easily accessible promising class of n-type materials.
RESUMEN
Herein, we demonstrate that with the widespread theme of residue patterning and stereochemical restraints of self-complimenting proteinogenic amino acids, a new and rich class of homomeric dipeptides exhibiting two-dimensional fluid aggregates with hierarchical ordering can be obtained. In particular, a simple way of achieving a class of functional dipeptides, wherein the first and the second residues chosen are L-/D-alanines and L-/D-leucines, has been accomplished. The supramolecules synthesized can be regarded as intermediates between polycatenars and taper-shaped amphiphiles because they possess two lipophilic segments interlinked by a peptide unit (spacer). Two pairs of enantiomers and their respective diastereomers derived from these amino acids are evidenced to self-organize into a helical columnar phase through hydrogen bonding by means of FTIR, UV/Vis, and chiroptical circular dichroism (CD) spectral analyses as well as by optical, calorimetric, electrical switching, and X-ray studies. The CD and X-ray studies have revealed that the form chirality (handedness) and the magnitude of out-of-plane fluctuations of the lattice planes of the fluid supramolecular columnar structures are solely directed by the stereochemistry encoded in the spacer. Of special significance, the less frequently found oblique helical columnar phase formed by a pair of enantiomers derived from L-/D-alanines, unlike those derived from other amino acids, exhibit ferroelectric behavior; the measured spontaneous polarization is as high as 440 nC cm(-2). Besides, all these supramolecules form stable organogels in ethanol and the CD and SEM studies on a representative gel suggest the presence of helical structures.
Asunto(s)
Dipéptidos/química , Rastreo Diferencial de Calorimetría , Dicroismo Circular , Microscopía Electrónica de Rastreo , Modelos Químicos , Estructura Molecular , Transición de Fase , Espectrofotometría , Espectrofotometría Infrarroja , Temperatura , Difracción de Rayos XRESUMEN
The first examples of monodisperse liquid crystalline pentamers, synthesized by covalently linking five mesogenic segments through four flexible spacers, exhibiting mono-/partially bilayered phases with unusual textures, as established by optical, calorimetric, and X-ray diffraction studies, are reported. Importantly, the two types of multifunctional pentamers, namely, unsymmetric and C2 symmetric are soluble in organic solvents and exhibit analogous electrochemical features.
RESUMEN
Novel, symmetrical, bent-core mesogens, namely substituted 1,3-phenylenebis{4'-[(ethoxycarbonyl)oxy]-1,1'-biphenyl}-4-carboxylates, are prepared with carbonate groups at both ends of the molecules. The mesophase properties are investigated for different electron-donating and -withdrawing substituents connected to the central ring at different positions. These compounds exhibit nematic and/or smectic A intercalated (SmA(int)) mesophases. Electro-optical studies show a very significant electric-field-induced biaxiality that is fast (<1 ms) and large (0.03) associated with a high birefringence (0.33 at 500 nm, 10 V mum(-1) field) for the unsubstituted analogue. For one substance this effect is observable from above 100 degrees C down to room temperature. Such electric-field-induced biaxiality may find practical applications in fast electro-optic modulation devices.
RESUMEN
The phase transitional behavior of two homologous series of five-ring banana-shaped compounds comprising fluorine substituents synthesized through covalent linking of two chemically dissimilar rod-like anisometric cores (arms) to central 1,3-phenylene is reported. The novelty of these molecules originates from the fact that the molecules are highly nonsymmetrical. One of the arms, which is either salicylaldimine or Schiff base core, possesses two vicinal fluorine atoms at the terminal ring having a -decyloxy tail; while the -alkyl tail attached to the other arm was varied to realize a homologous series of compounds. The mesophases have been characterized by several complementary studies. The banana-shaped systems having short or medium alkyl chain lengths form apolar columnar (two-dimensional) structures, while on ascending the series, a polar smectic phase is stabilized. Detailed electro-optical investigations on one of the polar smectic phases revealed a synclinic antiferroelectric (racemic) ground state structure, which switches, as expected, to an anticlinic ferroelectric state by the application of an electrical field. At higher field strengths applied for an extended time interval, the anticlinic ferroelectric state switches to a synclinic ferroelectric (chiral) state. Upon field removal, these domains switch to an anticlinic antiferroelectric (chiral) state, which eventually nucleates to the original antiferroelectric synclinic (racemic) state. Remarkably, the associated spontaneous polarization value exceeds 800 nC cm, which is among the highest reported hitherto.
RESUMEN
The first mesoionic nematic and smectic A mesogens derived from sydnones that are characterized by both covalent and ionic features have been synthesized and evidenced by optical, calorimetric and X-ray diffraction studies.
Asunto(s)
Cristales Líquidos/química , Sidnonas/química , Rastreo Diferencial de Calorimetría , Dimerización , Iones , Modelos Químicos , Estructura Molecular , Transición de Fase , Termodinámica , Difracción de Rayos XRESUMEN
A new class of discotic liquid crystals derived from tris(N-salicylideneanilines) existing exclusively in their C3h and Cs keto-enamine tautomeric forms is reported. These compounds self-assemble to form columnar liquid crystalline phases with a small core-core separation as evidenced by X-ray diffraction studies.
RESUMEN
The performance characteristics of a method for detecting opiates (morphine, codeine, heroin, and 6-acetylmorphine [6-AM]) in oral fluid specimens were examined and compared with methods for urine specimens. The oral fluid was easily obtained using a simple device that collects between 1 and 1.5 mL of fluid for laboratory analysis. Simultaneously collected specimens from 60 known opiate abusers from a drug-treatment center were first tested using an immunoassay cutoff of 10 ng/mL in oral fluids and 2,000 ng/mL in urine. Using a second aliquot, opiate confirmation in urine was performed by gas chromatography-mass spectrometry (GC-MS) and in oral fluids by GC-MS-MS. The combined immunoassay and GC-MS-MS procedures were completed with less than 250 pL of oral fluid. Opiates identified in oral fluid specimens from heroin users included morphine, codeine, heroin, and 6-AM. The immunoassay was tested for precision, stability, and the effects of potential cross-reactants. The results yielded 93.6% agreement between oral fluid and urine, suggesting that oral fluid may be a reliable matrix for opiate detection.