Search results for "Thermotropic crystal"

1988

Arylethynyl-Substituted Tristriazolotriazines: Synthesis, Optical Properties, and Thermotropic Behavior

2014

The synthesis of C3-symmetrical tristriazolotriazines with conjugated arms and lateral alkoxy side chains was performed by a threefold condensation of cyanuric chloride with tetrazoles. Conjugated π segments include phenyl, tolane, and its phenylethynyl-elongated homologue. Disclike and a dendritic molecule have been obtained, and two compounds with a 3,4,5-tris(octyloxy) substitution form broad thermotropic mesophases. The linear optical properties, solvatochromism of the fluorescence, acidochromism, and the two-photon absorption efficiency of selected compounds are reported.

Textures in hexatic films of nonchiral liquid crystals: Symmetry breaking and modulated phases

1994

Novel modulated textures, such as stripes and multiarmed star defects, have been observed in freely suspended films of nonchiral liquid crystals just below the smectic-$C$ to hexatic phase transition. Detailed studies using depolarized reflection microscopy suggest that the stripes are locally chiral surface splay domains of the smectic-$L$ phase, a tilted hexatic not previously identified in thermotropic liquid crystals. Line defects which form additional domain walls in the hexatic lattice lead to characteristic modulations of the basic one-dimensional stripe pattern. Inside thick circular islands, for example, stripes form circumferentially and the lines form centered 12-armed stars, res…

Kernspinlabel-Untersuchungen zur Struktur und Dynamik von flüssigkristallinen Hauptkettenpolymeren

1984

Thermotropic nematic polyesters, specifically deuterated at different positions of the polymer chain, were macroscopically aligned by strong magnetic fields and solid state extrusion. Analysis of the observed 2H NMR spectra was achieved, employing a dynamic NMR model, based on the stochastic Liouville equation. The model considers various double and multiple pulse sequences, recently employed in FT-NMR spectroscopy.

The Phase Behaviour of Amphiphilic Monolayers

1991

Amphiphilic monolayers display a wealth of condensed phases. It is only recently that these have been widely recognised as being distinct, but they are in fact quite analogous to the well-known lamellar gel phases of bulk lyotropic and thermotropic mesogens. An understanding of these phases has proved to be important for controlling the defect structure of the monolayers used in the fabrication of Langmuir-Blodgett films. This understanding is being achieved by developments in a number of techniques, including X-ray diffraction and isotherm miscibility. The phase diagrams of the materials studied so far are all very closely related, lending new credibility to the principle of corresponding …

Mesomorphic Donor-Acceptor-substituted 1,4-Distyrylbenzenes

2009

Conjugated oligomers with terminal donor-acceptor substitution attract increasing attention in organic chemistry because of their outstanding and not seldom unexpected properties in materials science [1 – 4]. Although a variety of oligo(1,4-phenylene-vinylene)s with terminal donor-acceptor substitution (DAOPVs 1, Scheme 1) are known [5 – 22], the number of thermotropic liquid crystals among them is very low and is confined to monomers (n = 1), that means to certain push-pull substituted (E)-stilbenes [23 – 31]. The behavior of conjugatedmolecules, which are highly polar and form mesophases by self-organization, is very interesting for various applications of liquid crystals [3]. A big disad…

Insights into the anion effect on the self assembly of perylene bisimide diimidazolium salts

2017

Abstract We studied how changing the anion affects the self-assembly of three diimidazolium salts bearing a perylene bisimide spacer. In particular we used [BF 4 − ] and [NTf 2 − ] based salts together with a mixed salt bearing both [I − ] and [BF 4 − ] anions. Thermal as well as concentration and temperature dependent spectroscopic investigations revealed that changing the anion impacts on solid state and solution aggregation, leading to articulate thermotropic behaviors and contrasting solvent effects, respectively. We also studied the electrochemical behavior of the salts to verify if changing the anion alters the redox properties of the salts. Finally, different anions also lead to very…

4,4′‐Distyrylazobenzol als Mesogen

1992

4,4′-Distyrylazobenzene as Mesogen From 3,4-dihydroxybenzaldehyde (1) the tetraalkoxy-substituted 4,4′-distyrylazobenzenes (E,E,E)-5a – c are synthesized. A similar reaction sequence leads from ethyl 3,4,5-trihydroxy-benzoate (6) to the hexaalkoxy-substituted 4,4′-distyrylazobenzenes (E,E,E)-11 b, c. With the exception of 5a all products show thermotropic LC properties. Smectic phases have been characterized by polarizing microscopy and by differential scanning calorimetry.

INTERACTION OF MACROMOLECULAR PRO-DRUGS WITH LIPID MODEL MEMBRANE - CALORIMETRIC STUDY OF 4-BIPHENYLACETIC ACID LINKED TO ALPHA,BETA-POLY(N-HYDROXYET…

1990

The effect of 4-biphenylacetic acid (BPAA) covalently linked to α,β-poly(N-hydroxyethyl)-dl-aspartamide (PHEA) on the thermotropic properties of dipalmitoylphosphatidylcholine (DPPC) liposomes was investigated by differential scanning calorimetry (DSC). Addition of increasing amounts of PHEA-BPAA adduct to a suspension of phospholipid vesicles modified the thermotropic gel-to-liquid crystalline phase transition by decreasing the enthalpy changes ΔH with concomitant broadening of the peak without variations in the transition temperature (Tm). These effects are interpreted in terms of a deep interaction of BPAA bound to the polymer with the apolar moiety of the lipid bilayer. The amount of dr…

Dysprosium-Based Ionic Liquid Crystals: Thermal, Structural, Photo- and Magnetophysical Properties

2009

[C12mim]3[DyBr6] (C12mim = 1-dodecyl-3-methylimidazolium) represents a new material with interesting luminescent behavior as well as mesomorphic and magnetic properties. The compound was found to show thermotropic liquid crystalline behavior and forms smectic mesophases which were investigated by hot-stage polarizing optical microscopy and differential scanning calorimetry. The emission color of [C12mim]3[DyBr6] can be tuned from white to orange-yellow by the choice of the excitation wavelength. Sample excitation with λex = 366 nm leads to the blue-whitish luminescence from the imidazolium cation itself. With λex = 254 nm the common Dy(III) emission is observed which mainly arises from the …