A first low-molar-mass, monodispersive, bent-rod dimer exhibiting biaxial nematic and smectic A phases

A "peelable banana" is formed when a bent-core molecule is linked to a rodlike mesogen through a flexible aliphatic spacer. This is an appropriate description of this novel low-molar-mass organic system, which displays a transition from a biaxial nematic (Nb) phase to a biaxial smectic A phase. The illustration gives a schematic representation of the dimeric molecules in the Nb phase as well as the corresponding textural and conoscopic patterns obtained

Photo-controlled Conformation-assisted Permanent Optical Storage Device Employing a Polymer Network Liquid Crystal

A new type of optical storage device is described employing a material consisting of a host nematic liquid crystal, a photoisomerisable azobenzene component and a photopolymerizable monomer. The principle of image storing involves selectively controlling the birefringence of the medium immediately prior to photopolymerization of the monomer. We show that photoisomerisation driven nematic to isotropic transition can be employed to achieve this through proper timing of the reverse isomerization of the azobenzene compound before the nematic director fluctuations get quenched. It is also suggested that grey-shades can be created in this device using the recently discovered phenomenon of electric-field acceleration of reverse isomerisation

Design, control and performance comparison of PI and ANFIS controllers for BLDC motor driven electric vehicles

The research and usage of electric vehicles (EVs), including two and four-wheeler vehicles, are rapidly increasing worldwide as alternatives to oil/gas-based vehicles. Brushless direct current (BLDC) motors are popular for industrial and traction applications due to their inherent advantages. In EVs, achieving low error in steady-state and transient responses is crucial for smooth acceleration at the wheel. This paper presents the design and control of a BLDC motor for speed control during acceleration and deceleration, considering error as a key factor in the MATLAB/Simulink environment. Proportional-integral (PI) and fuzzy controllers are commonly used for motor control to improve steady-state and transient performance, thereby reducing error. In this study, the PI and adaptive neuro-fuzzy inference system (ANFIS) controllers are designed and compared for a 5-kW, 48-V, and 100-Amp BLDC motor in EV applications. The results demonstrate that the ANFIS controller enhances the dynamic performance of the BLDC motor and improves other operating characteristics such as rise time, settling time, peak overshoot percentage and the vehicle response in terms of speed and distance

Formation of highly luminescent supramolecular architectures possessing columnar order from octupolar oxadiazole derivatives: hierarchical self-assembly from nanospheres to fibrous gels

The synthesis and study of the liquid crystalline, photophysical, and aggregation behavior of novel octupolar oxadiazole derivatives are reported. These molecules formed columnar mesophases at elevated temperatures which transformed into a glassy state at ambient temperatures wherein the columnar order was retained. Their spontaneous concentration dependent hierarchical self-assembly from spheres to fibrous gels has been investigated using TEM, SEM, and XRD. Retention of the hexagonal columnar (Col<SUB>h</SUB>) order was also observed in the fibrous aggregates. Concentration dependent luminescence spectral studies indicated that the change in morphology from spheres to fibrous aggregates was associated with a shift in chromophore packing from predominantly H-type to J-type aggregates. Time resolved anisotropic investigations revealed that the columnar stacking of molecules in the aggregated state provided a pathway for excitation energy migration to the lower energy J-traps

New 4-(2-(4-alkoxyphenyl)-6-methoxypyridin-4-yl) benzonitriles: synthesis, liquid crystalline behavior and photo physical properties

A new series of luminescent 4-(2-(4-alkoxyphenyl)-6-methoxypyridin-4-yl) benzonitriles containing three ring systems, viz. methoxy pyridine, benzonitrile and alkoxy benzene with variable alkoxy chain length, with bent-core structures were synthesized as potential mesogens and characterized by spectral techniques. Their liquid crystalline behavior was investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and variable temperature powder X-ray diffraction (PXRD) measurements. The study reveals that compounds with shorter chain lengths i.e. m = 4] exclusively exhibit the nematic phase while compounds with longer chain lengths i.e. m = 6-14 (only even)] show predominantly the orthorhombic columnar phase. Single crystal X-ray analysis of 4-(2-(4-butyloxy/octyloxyphenyl)-6-methoxypyridin-4-yl) benzonitriles reveals that they possess slightly non-planar unsymmetrical bent structures and their molecular packing consists of nonconventional H-bond interactions; it also explains the observed liquid crystalline phase. An optical study indicates that the title compounds are good blue emitting materials showing absorption and emission bands in the range 335-345 nm and 415-460 nm, respectively. An electrochemical study of 4-(2-(4-octyloxyphenyl)-6-methoxypyridin-4-yl) benzonitrile shows a band gap of 1.89 eV with HOMO and LUMO energy levels of -5.06 and -3.17 eV, respectively. Also, density functional theory (DFT) calculations confirm its optimized geometry, electronic absorption and frontier molecular orbital distributions

Influence of modifier oxides on spectroscopic features of Nd2O3 doped PbO-Ro2O3-WO3-B2O3 glasses (with Ro2O3 = Sb2O3, Al2O3, and Bi2O3)

The influence of modifier oxides (Ro2O3 = Sb2O3, Al2O3, and Bi2O3) on the spectral analysis of PbO-Ro2O3-WO3-B2O3 glasses doped with Nd3+ ions is investigated in this work. Samples were prepared by the melt quench method, and their optical, luminescence, and physical properties were examined. From the measured properties, it is observed that the density and refractive index of the studied glasses vary non-linearly with the concentration of Nd2O3, leading to the formation of cross-linked networks under the polaraisability of the oxide glasses. The optical band gap (E_0) and Urbach energy (¿E) was determined by using UV-visible spectra; it also varies non-linearly based on the modifier oxides and the formation of non-bridging oxygen ions. The oscillator strengths of the absorption bands were determined by the Judd-Ofelt model, and the three intensity parameters O_2, O_4, and O_6 were calculated for each glass. From these parameters, the transition probability (A_t), radiative life time (t_rad), branching ratio (ß_r), quantum efficiency (¿), and non-radiative decay rate (W_NR) were calculated. From these results, it can be concluded that the studied glasses can be used for laser and optical applications.Peer ReviewedPostprint (author's final draft

Effect of modifier oxides on spectroscopic and optical properties of Pr3+ doped PbO-Ro2O3-WO3-B2O3 glasses (with Ro2O = Sb2O3, Al2O3, and Bi2O3)

Praseodymium (Pr2O3) doped PbO-Ro2O3-WO3-B2O3 glasses were prepared by melt quenching method and their optical absorption and emission spectra were characterized, for three different heavy metal oxides (Ro2O3 = Sb2O3, Al2O3, and Bi2O3). The characteristics of the glass matrix are confirmed by X-ray diffraction spectra. Many structural properties can be identified by Fourier Transform infrared spectra of the glasses, such as PbO, B2O3, and WO3. From the optical absorption spectra, the absorption edges, and the values of direct and indirect band gap transitions and Urbach energies were calculated. The oscillator strengths of the absorption bands were determined by the Judd-Ofelt model, and the Judd-Ofelt intensity parameters O_2, O_4, and O_6 were calculated for each of the studied glasses. Moreover, the nephelauxetic ratio ß, bonding parameter d, and optical basicity ¿^th were also calculated to characterize the bonding nature of the Pr3+ rare-earth ions. From the emission spectra, spontaneous radiative transition probability A_t, total radiative transition probability A_T, luminance branching ratio ß_r, and radiative life time t_rad were calculated. From the spectra, the CIE color coordinates were also calculated for all the studied glasses. This research confirms that the studied materials are suitable for red laser applications.Postprint (updated version