Studies on Induced Smectic Phases (II) Transition Enthalpies,X-ray Patterns and Layer Spacings of Orthogonal Phases of Binary Mixtures of Nematogens with Contrasting Dielectric Anisotropies

Binary mixtures of two nematogens, 4,4′-di-n-heptyl-azobenzene with 4-n-pentyl-4′ -cyano biphenyl were studied by optical, calorimetric and X-ray measurements. At a given concentration induced phases with a sequence S_A, S_B, S_E were detected, the properties of which were discussed.     

Thermotropic Liquid Crystalline Compounds with Lateral Long Chain Substituents (VII). X-Ray Studies in 1,4-Bis-(4-n-oetyloxybenzyoloxy)-2-n-alkylbenzenes

X-ray studies in substances with the general formula in the nematic states were performed. The results prove the existence of cybotactic groups despite the fact that the branched substances do not show smectogenic properties. We propose a model for the packing of the molecules, which explains the influence of the lengths of the lateral branches on the structure of the cybotactic groups.     

Thermotropic liquid crystalline compounds with lateral long-chain substituents (IV). Physical properties of 1,4-bis-[4-n-octyloxybenzoyloxy]-2-n-alkylbenzenes

In 15 Substances of general formula transition temperatures, transition enthalpies and entropies, densities and phase transition volumina, order parameters of a dissolved dye and optical refractive indices were measured. Additional miscibility and X-ray investigations were performed. The results are discussed on the basis of molecular statistical theories of the nematic state and point to a conformation of the long lateral chains which is nearly parallel to the molecular long axes. The results further show the dominating importance of the steric repulsive forces in stabilizing the nematic state.     

Stabilization and destabilization of the SA phase in mixtures of 4-nitrobenzyl-2,5-bis(4-n-alkyloxybenzoyloxy)benzoates

4-Nitrobenzyl-2,5-bis(4-n-alkyloxybenzoyloxy)benzoates exhibit S_A phases which are characterized by an antiparallel packing of the molecules and a partial intercalation of the terminal alkyl chains. In binary systems of selected rod-like components the S_A mixed phase can be stabilized or destabilized depending on the molecular length of the rod-like molecules. This unusual behaviour is mainly due to steric interaction and can be interpreted by a simple packing model.     

A new type of square columnar liquid crystalline phases formed by facial amphiphilic triblock molecules

A series of three novel liquid crystalline amphiphilic molecules is reported which are composed of three incompatible molecular parts, a rigid terphenyl core, two lipophilic decyloxy chains in the terminal 4- and 4' '-positions, and a polar group in the lateral 2'-position. The polar group comprises a polyether chain, an amide group, and a polyhydroxyalkyl end group (1-acylamino-1-deoxy-d-sorbitol derivatives). The self-organization of these compounds was studied by polarized light microscopy, differential scanning calorimetry, and different X-ray diffraction techniques. These investigations confirm a novel liquid crystalline phase with a square 2D-lattice (square columnar mesophase, plane group p4mm). This structure is built up by a set of three distinct columns, namely columns containing the polar lateral groups, columns incorporating the alkyl chains, and ribbons of the rodlike terphenyl units. The calamitic cores form walls bounding square-shaped channels occupied by the microsegregated polar lateral chains. The lipophilic columns containing alkyl chains are at the corners interconnecting the aromatic rods end-to-end.     

Thermotropic and lyotropic liquid crystalline phases of rigid aromatic amphiphiles

Rodlike amphiphilic molecules that contain exclusively aromatic building-blocks and no flexible alkyl chains have been synthesized and their mesomorphic properties investigated. These novel compounds bear diol head groups of different size (2,3-dihydroxypropyloxy or 5,6-dihydroxy-3-oxahexyloxy groups) at one end of a biphenyl unit, various aromatic segments (benzyloxy, 4-, 3-, or 2-methylbenzyloxy, phenoxy groups) at the other, and additional methyl substituents in different positions. They were synthesized by using Suzuki cross-coupling reactions as the key steps. Their thermotropic mesomorphism was investigated by means of polarized light optical microscopy, differential scanning calorimetry, and, for enantiotropic phases, by X-ray scattering. The liquid crystallinity of this class of compounds is influenced by protic solvents, such as water and glycerol. Dependent on the temperature and the solvent content, different SA phases were found. Several mesophases resulting from the frustration of these layer structures (e.g., different columnar phases, optical isotropic mesophases, and nematic phases) were also present. The smectic phases have different degrees of intercalation (SAd, SA2). The columnar phases are supposed to be ribbon structures that result from the collapse of the smectic layers. They occur in some pure compounds or they are induced upon the addition of protic solvents. The particular phase sequences of the different compounds depend mainly on the position of the methyl substituents at the biphenyl cores and are largely determined by the degree of intercalation of the aromatic cores.     

SmA-SmC-B2 polymorphism in an achiral cyano substituted banana-shaped mesogen

A new achiral five-ring banana-shaped mesogen is presented which has a cyano substituent in the 4-position of the central core. Microscopical, X-ray, dielectric and electro-optical investigations give evidence for the unusual phase sequence B₂, SmC, SmA. The B₂ phase shows an antiferroelectric switching behaviour; the spontaneous polarization was found to be 330 nCcm^-2.     

Large-scale synthesis of high purity “Phos reagent” useful for oligonucleotide therapeutics

A large-scale, cost-effective, and environmentally clean synthesis of high purity 2-cyanoethyl-N,N,N′,N′-tetraisopropylphosphorodiamidite (Phos reagent) has been accomplished on a commercial scale. Treatment of PCl₃ with diisopropylamine followed by 3-hydroxylpropionitrile furnished the Phos reagent in excellent yield. The ³¹P NMR of the Phos reagent prepared at large-scale show consistent purities >99% when several key factors are controlled. These controlling factors include sourcing high purity key raw materials, identification and elimination of critical impurities, stability and storage of Phos reagent.