Synthesis and characterization of new aromatic esters based on 4,16-pregnadiene-6,20-dione skeleton

A series of new aromatic esters based on 4,16-pregnadiene-6,20-dione skeleton, namely 3β-benzoyloxy-4,16-pregnadiene-6,20-dione and 3β-furoyloxy-4,16-pregnadiene- 6,20-dione, which may be good inhibitors for the 5α-reductase enzyme and show high antiandrogenic activity, were synthesized starting from diosgenin. The structures of the steroids were characterized by elemental analysis, 1H NMR, 13C NMR, IR and mass spectrum. Single crystal X-ray diffraction measurement on one of the new compounds, 3β-(p-methoxybenzoyloxy)-4,16-pregnadiene-6,20-dione revealed that the A, B, C, and D ring adopted half chair, distorted chair, distorted chair, and distorted envelope conformation, respectively. The molecules in the crystal were packed face-to-face at the normal van der Waals distances

A double-layer light shutter consisting of polymer dispersed liquid crystal and azo dye/quantum dot

We have developed a double-layer liquid crystal light shutter and investigated its temperature dependent morphological, electro-optical, and dielectric properties. The optical layers of the shutter are in direct contact, reducing optical losses. The shutter comprises a polymer dispersed liquid crystal film adjacent to an azo dye methyl red and CdSeS/ZnS quantum dot doped cholesteric liquid crystal layer. This novel double-layer light shutter device is switchable between opaque and transparent states at room temperature, and it exhibits low threshold and saturation voltages. Both the threshold (Vth) and saturation (Vsat) voltages are found to decrease with increasing temperature. The electrical characteristics of the shutter, namely the real part of dielectric constant (ε′) and the ac conductivity (σac) also increase with temperature in the low frequency region. Our results show that this double-layer light shutter has interesting potential for simple electro-optical devices and smart window applications

Flexoelectric coefficients enhancement via doping carbon nanotubes in nematic liquid crystal host

Flexoelectric coefficients of carbon nanotube (CNT) doped nematic liquid crystals (NLCs) are studied based on the Helfrich theory. Weak and hard anchoring conditions between the NLC molecules and CNTs are considered. The volume fraction of the CNTs in nematic host is assumed to be low, which makes nanotubes aggregation phenomena negligible. Also, the length of doped CNTs is assumed to be lower than 10μm, so these rigid rods with low concentration cannot possess any flexoelectric polarization by themselves, only their presence modifies the flexoelectric coefficients of the NLC system. The Landau-de Gennes theory is used to calculate the order parameter changes in the medium. Also, the numerical density definition is renewed in the presence of nanotubes. It is shown that in the nematic phase the flexoelectric coefficients increase along with the increase of the coupling strength and temperature. The enhancement in flexoelectric coefficients is more significant in hard anchoring conditions than in the weak anchoring case. The flexoelectric coefficients increase up to 5-fold is calculated near the phase transition temperature, which is in good accordance with the experimental reported data