Dendritic liquid crystal

Keywords Dendrimer Dendritic Liquid crystal Mesogen Mesophase Polypede... 

Typically tri-, tetra-, penta-, etc., substituted supermolecules are used as dendrons in the formation of dendritic liquid crystals. Figure 8 shows an example of a dendron that was created to attach to a scaffold in order to prepare a dendromesogen [25]. In this case, three cyanobiphenyl mesogens... 

Often dendritic liquid crystals are assembled through the preparation of den-drons, and then the dendrons are attached to a central scaffold of a suitable generation number. This technique allows for the dendrons to be prepared on a large scale and then the attachments to the scaffold are done in smaller number than if the mesogens are directly attached. However, one problem that is sometimes encountered in this synthetic approach is that the scaffold becomes progressively crowded as the dendrons are attached, and sometimes this can lead to incomplete derivatization. In the following section, complete and incomplete substitutions are investigated and compared. 

Figure 2. Structure of liquid crystalline block copolymers (LC-BCPs) (A) rod-coil diblock copolymer (B) rod-coil diblock copolymer with flexible spacer in the rod block (C) side group liquid crystal-coil (SGLC- coil) diblock copolymers (D) coil -rod-coil ABC triblock copolymers (predicted to be novel ferroelectric fluid by R. G. Petschek and K. M. Wiefling, Phys. Rev. Lett., 1987, 59(3), 343-346) (E) rod-rod diblock copolymer (one example of well-defined po-ly(n-hexyl isocyanate-fc-n-butyl isocyanate) rod-rod diblock copolymer was given by Novak et al. [68], however, no morphology studies were reported) (F) dendritic liquid crystal-coil (DLC-coil) diblock copolymer (not reported).

Abstract We describe mechanochromic and thermochromic photoluminescent liquid crystals. In particular, mechanochromic photoluminescent liquid crystals found recently, which are new stimuli-responsive materials are reported. For example, photoluminescent liquid crystals having bulky dendritic moieties with long alkyl chains change their photoluminescent colors by mechanical stimuli associated with isothermal phase transitions. The photoluminescent properties of molecular assemblies depend on their assembled structures. Therefore, controlling the structures of molecular assemblies with external stimuli leads to the development of stimuli-responsive luminescent materials. Mechanochromic photoluminescent properties are also observed for a photoluminescent metallomesogen and a liquid-crystalline polymer. We also show thermochromic photoluminescent liquid crystals based on origo-(/ -phenylenevinylene) and anthracene moieties and a thermochromic photoluminescent metallocomplex. 

Several cyclopropanated organofullerene materials have been synthesized for the preparation of fullerene-containing thermotropic liquid crystals. A wide variety of such liquid-crystalline materials were synthesized possessing mono-140-42], hexa-addition [43] pattern, or even dendritic addends [44-46]. 

Non-covalent thermotropic liquid crystal dendritic systems have been achieved recently by converting the amphiphihc surface of the dendrimers (-NH2) into a hydrophobic shell (alkanoate chains). Tomalia et al. reported on the non-aqueous lyotropic behavior of supramolecular complexes re-... 

As noted above, various morphologies have been documented for dendritic and hyperbranched liquid crystal polymers, and this topic has recently received intense interest [ 14-27, 62-70]. Although the exhaustive revision of this area is outside the scope of this article, several types can be easily identified ... 

Dendritical molecules can also assemble into supramolecular columnar liquid crystals [2, 27, 61, 62]. For example, dendritic oligo(glutamic acid) derivatives 40a-c can self-assemble into columnar LC stmctures [62]. Hydrogen bonding between the amino acid residues and nanosegregation of incompatible molecular blocks, polar amino acid moieties, and Upophilic alkyl moieties is the driving forces for the supramolecular LC assemhhes. 

Solvent molecules are frequently found in association with precipitated materials. For example, crystalline substances often form with water molecules located at specific sites, e.g. water of crystallization, held in co-ordination complexes around lattice cations. Extraneous inclusion of water molecules can occur if a co-precipitated cation carries solvation molecules with it. Massive incorporation of solvent, together with other soluble impurities can occur in random pockets (inclusions) as a result of the physical entrapment of mother liquor. Fast crystal growth, leading to growth instabilities, dendrite formation, crystal agglomeration, etc., can all contribute to this undesirable feature. An account of liquid inclusions in crystals is given in section 6.6. 

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