New mesogenic compounds having fork-like or cyclic amide terminal groups

Two homologous series of mesogenic materials with molecules containing an amide moiety, cyclic or symmetrically branched, as the terminal group have been synthesized. Materials of both series form lamellar liquid crystal phases. It was observed that elongation of the amide chains in 'fork-like' compounds destabilizes the mesophases, while 'cyclic' materials, even with quite large terminal amide rings, exhibit enantiotropic liquid crystalline phases.     

A traceless solid-supported synthesis of novel pyrazinediazepinedione derivatives

A simple, convenient, six-step synthesis of novel, tricyclic pyrazinebenzodiazepinedione derivatives has been described. The strategy is based on the use of the orthogonally-protected, optically pure, (S)-piperazine-2-carboxylic acid, in a Petasis reaction, followed by coupling with anthranilic acid and finally cyclizing cleavage. The investigated method was applied for the synthesis of novel bicyclic pyrazinediazepinedione derivatives. This traceless, solid-supported approach allows the preparation of a wide variety of compounds in moderate yields from commercially available or easily obtainable reagents.     

Spontaneous breaking of minimal surface condition: labyrinths in free standing smectic films

We present a study of thin free standing films made of intercalated smectic-C liquid crystal in which, upon lowering the temperature, the minimal surface area condition is broken. A periodic modulation of the film thickness is obtained and a labyrinth structure of crests and valleys is formed. Thickness variation is coupled to the spatial variation of the molecular orientation. The transition to the labyrinth structure is explained to be driven by the mass density difference between the surface and the bulk layers.     

Preparation of C-5-substituted 6,5′-O-anhydrouridine by Sn-Pd transmetallation-coupling process and their use

The palladium-catalyzed reaction of 5-tributylstannyluridine derivative (9) with a variety of aryl, vinyl halides provides an efficient method for the synthesis of the corresponding 5-substituted 6,5′-O-anhydrouridines. Additionally the 5-fluoro 6,5′-O-anhydrouridine (16) via fluoro-destannylation with Selectfluor is described. A dialkylphosphonate moiety was then introduced at C5 from the allyl derivative 10a under cross-metathesis conditions.     

Electric-field-induced polar biaxial order in a nontilted smectic phase of an asymmetric bent-core liquid crystal

A polarization reorientation process has been studied by means of optical second-harmonic generation in an optically uniaxial smectic phase of an asymmetric bent-core liquid crystal. A nontilted polar smectic order with a biaxial order is induced by applying an electric field to the uniaxial nonpolar smectic phase. This phenomenon was well simulated by the two-dimensional Langevin process, i.e., electric-field-induced continuous molecular reorientation against thermal agitation. The simulation suggests that about 200s of molecules form a polar domain and cooperatively respond to the applied field. The existence of the polar domains and their reorientation are consistent to the dielectric measurement; a high dielectric constant of about 60 at the kHz range is markedly suppressed by applying a bias field.     

Pictet-Spengler reaction of biogenic amines with (2R)-N-Glyoxyloylbornane-10,2-sultam. Enantioselective synthesis of (S)-(+)-N-methylcalycotomine

(2R)-N-Glyoxyloylbornane-10,2-sultam reacted with dopamine hydrochloride, forming the Pictet-Spengler condensation product, which was further converted into (S)-(+)-N)-methylcalycotomine of high enantiomeric purity. The same kind of reaction with tryptamine hydrochloride gave the condensation product with 100% d.e.     

Monolayer Filaments versus Multilayer Stacking of Bent‐Core Molecules

Bent‐core materials exhibiting lamellar crystals (B4 phase), when dissolved in organic solvents, formed gels with helical ribbons made of molecular monolayers and bilayers, whereas strongly deformed stacks of 5–6 layers were found in the bulk samples. The width and pitch of the helical filaments were governed by molecular length; they both increased with terminal‐chain elongation. It was also found that bulk samples were optically active, in contrast to the corresponding gels, which lacked optical activity. The optical activity of samples originated from the internal structure of the crystal layers rather than from the helicity of the filaments. A theoretical model predicts a strong increase in optical activity as the number of layers in the stack increases and its saturation for few layers, thus explaining the smaller optical activity for gels than for bulk samples. A strong increase and redshift in fluorescence was detected in gels as compared to the sol state.     

Double gyroid structures made of asymmetric dimers

Gyroid cubic phases are interesting for both scientists and engineers due to possible applications in electronic devices. New series of dimeric molecules, despite their flexible molecular structure, can display double gyroid cubic phase with Ia3d symmetry and lattice parameter corresponding to double molecular length. The cubic phase is structurally related to columnar phase and both phases often coexist in the same temperature window. Apparently, for studied compounds stronger molecular asymmetry promotes cubic structure. Interestingly, for the examined compounds the transition between two isotropic liquids was observed.     

Liquid‐Crystalline Phases Made of Gold Nanoparticles

Spontaneous formation of smectic and columnar structures was observed when spherical gold nanoparticles were functionalized with mesogenic thiols (see layered structure and X‐ray pattern of a sample in smectic phase). The particle ordering is stimulated by softening of the interparticle potential and flexibility for deformation of the grafting layer.

     

Molecular factors responsible for the formation of the axially polar columnar mesophase Col(h)P(A)

The structure of hexacatenar bent-shape molecules has been systematically modified in order to determine the main molecular factors responsible for the appearance of the axially polar columnar mesophase. It was found that the stability of the polar phase is very sensitive to the subtle modifications of the molecular shape: the phase is solely preserved if the modification is made at the terminal parts of the mesogenic core, whilst any other modifications destabilize the phase. It can be concluded that the main factor driving the transition between the phase made of flat supramolecular discs and the axially polar phase made of the cone-like units is the ability to fulfill close packing conditions in order to eliminate voids between neighboring molecular rigid cores.