Synthesis and Mesomorphic Behavior of Calamitic Liquid Crystals with a Biphenyl Moiety

A new mesogenic homologous series having a biphenyl moiety has been synthesized by condensing 4-hydroxy-4′-nitrobiphenyl- and methoxy-substituted 4-n-alkoxy cinnamoyl chlorides, and their liquid crystalline properties have been studied. All the members of the series are enantiotropic liquid crystals. The methyl to n-pentyl derivatives exhibit both Smectic A (SmA) and Nematic (N) phases; the higher members, starting with the n-hexyl derivative show only a SmA phase. The plot of transition temperatures versus number of carbon atoms in the alkoxy chain exhibits zig-zag pattern for Sm-N and N-Isotropic (Iso) transition temperature curves. The average thermal stability is compared with other related homologous series. The introduction of polar nitro group increases significant intermolecular force of attraction which stabilizes the molecular orientation. This results into the increase in the thermal stability of the system.     

Design of bicontinuous donor/acceptor morphologies for use as organic solar cell active layers

In recent works, we demonstrated the achievement of bicontinuous donor/acceptor morphologies by the addition of conjugated block copolymers to a blend of conjugated homopolymer donors and fullerene acceptors. However, the domain sizes resulting in experiments were much larger than those of interest for high‐performance organic solar cells. Moreover, a significant concentration of fullerene acceptors was present in the donor domains. Here, we utilize simulations to study the bicontinuous donor/acceptor morphologies that result for different parametric conditions. Using such results, we provide guidelines for how to blend polymer materials to give rise to bicontinuous phases with the smaller and more compositionally pure domains that are desirable for organic photovoltaic applications. Our results can be generalized to treat a large range of donor and acceptor monomers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 884–895     

Thermal racemization of biaryl atropisomers

Many biaryl compounds possess atropisomerism due to the steric hindrance of substituents at the ortho-position of the two aromatic moieties. Upon heating, atropisomers may have enough energy to surpass the rotational energy barrier and racemize. The thermal stability of five atropisomers was studied using chiral chromatography by following the change in enantiomeric excess ratio at different temperatures. The first order racemization reaction rate was obtained at a given temperature as the slope of the change in enantiomeric excess ratio versus time. For each atropisomer, the racemization rates at different temperatures led to the value of the rotational energy barrier for racemization, ΔG³, and to the racemization half lifetime, t_1/2, indicating the atropisomer thermal stability. Binaphthol started to racemize significantly at temperature of 190 °C and above while binaphthyldiamine was much more stable showing little or very minor racemization up to 210 °C. A chloro-substituted phenylamino-naphthol was very sensitive to thermal racemization starting at a low 40 °C.     

Keteniminium Salts as Key Intermediates for the Efficient Synthesis of 3-Amino-Indoles and -Benzofurans

Herein, we describe a high yielding approach towards the synthesis of 3-amino-indoles and -benzofurans through 6π-electrocyclization. This was made possible by taking advantage of the high reactivity of keteniminium salts, formed in-situ by treating with triflic anhydride and 2-fluoropyridine amides bearing at the α-position either an aniline or a phenoxy moiety. These mild conditions, on top of furnishing rapidly the 3-aminobenzoheteroles, allow the tolerance of various functional groups. Control experiments were carried out to highlight that the keteniminium is, indeed, in most cases, the reactive intermediate and conformational preferences of such species were investigated through a DFT study.     

All-inorganic solid-state electrochromic devices: a review

Electrochromic devices (ECDs) are currently attracting much interest in academic and industry for both research and their commercial applications because of their controllable transmission, absorption, and/or reflectance. This paper reviews the progress that has taken place from 1969 until the year 2015 with regard to all-solid-state inorganic ECD fabrication. The main aim of this review article is to provide an easy entrance to literature of all-inorganic solid-state ECD.     

Mesomorphism dependence on central bridge and tail ended polar group

Abstract

Severe operation conditions in the agriculture industry and numerous influencing factors complicate the selection of a contact material for switching devices. Attempts have been made to change the Ag-CdO contact material to a less toxic one. Environmentally friendly copper-base contact materials have been created for devices, which operate in agricultural electric systems, meanwhile being low-cost and with pre-set level of reliability in terms of transient resistance.     

Shear fracture of polystyrene melts and solutions

We find that symptoms of polymer melt fracture, such as a time-dependent decrease in apparent sample modulus and apparent slip, can be induced by oscillatory torsional shearing flow of polystyrene melts and solutions, even when the polymer molecular weight is below the entanglement threshold, and thre strain amplidute is as low as 3%. Visualization of samples during and after fracture show crack and bubble formation, as well as delamination of the polymer from the rheometer tools. For polystyrene melts, the critical stress for fracture is ^* 0.1–1.0 MPa, depending on polymer molecular weight and temperature, and for solutions it is as low as 5 × 10³ Pa. Since constitutive instabilities require the viscoelastic properties to be highly nonlinear, our observations of melt fracture in unentangled polymers at shearing strains well within the linear viscoelastic range rule out this mechanism for some of our experiments, and show that melt fracture is not always caused by constitutive instabilities.