Non-conventional liquid crystals—the importance of micro-segregation for self-organisation

Abstract

Selected examples of recently synthesised non-conventional liquid crystals are highlighted. These are cyclic and open chain oligoamides, molecules containing tetrahedral or octahedral central cores, dendrimers, polyhydroxy amphiphiles, taper shaped molecules, liquid crystals with perfluorinated or oligosiloxane segments, rod-coil molecules as well as special types of polycatenar and laterally branched calamitic molecules. Their mesomorphic properties are discussed as a consequence of incompatibility, micro-segregation and space filling. The analysis is based on the general concept of amphiphilicity, which describes any chemical or structural contrast within a molecule, such as hydrophilic/lipophilic, polar/non-polar, hydrocarbon/fluorocarbon, oligosiloxane/hydrocarbon or rigid/flexible. These non-conventional liquid crystals will be regarded as block molecules. Depending on the degree of chemical and structural difference and the size of the different building blocks micro-segregation can occur with formation of lamellar, columnar or spheroidal aggregates which organise to smectic, columnar and cubic mesophases. The striking analogies between the polymorphism of thermotropic and lyotropic liquid crystals and block-copolymers are pointed out. mers).12 More recently the interest in thermotropic and/or

Mesomorphic Hexabenzocoronenes Bearing Perfluorinated Chains

“…As a result, the introduction of perfluoroalkylated groups into large discotic PAHs paves the way toward the possibility of tuning their liquid crystalline phases into various ones which have been detected, so far, for smaller aromatic molecules bearing fluorinated groups. [41][42][43] …”

Hydrogen bond-directed aggregation of diazadibenzoperylene dyes in low-polarity solvents and the solid state

“…Nevertheless, as shown recently, the binding constants of hydrogen bonds increase considerably with decreasing competition of the solvent with the receptor groups, which is given, for example, in aliphatic solvents (5). If additional weaker interactions such as -interactions or microphasesegregation (19,20) favorably contribute to the self-assembly process, then a hierarchical superstructure formation becomes likely in the solid state or even in dilute solution.In the given contribution, highly fluorescent diazadibenzoperylene dyes 1a,b (21) were chosen as a ditopic hydrogen-bond acceptor, and their interaction with ditopic hydrogen-bond donating isophthalic acid 2 (22) § was studied in solution and the solid state (Fig. 1).…”

“…This finding implies that the dyes are tightly packed with a close distance of their -conjugated systems, which is 3.76 Å, according to WAXS. Furthermore, from the structural point of view [1a⅐2] assemblies are expected to give rise to microphasesegregation (19,20) because of strong contrasts in the polarity of the polar diazadibenzoperylene and isophthalic acid core units and the nonpolar aliphatic chains of 2. The lamellar period of 28 Å found in x-ray scattering at temperatures higher than 183°C fits to the size of the assemblies with extended alkyl chains.…”

Synthesis of Cu(II) and Ni(II) Phthalocyanines Bearing Nitro and 4-(1-Methyl-1-phenylethyl)phenoxy Groups

“…Nevertheless, the mesophase was formed due to the filling of free volumes at the periphery of the columns with mobile aromatic substituents. [25] All these compounds had only electron-donating fragments (from 4 to 8). A typical example of the FSLM compound is the 2,9,16,23-tetra[4-(1-methyl-1-phenylethyl) phenoxy]phthalocyanine copper(II) complex.…”