Counterion Effects on the Columnar Mesophases of Triphenylene‐Substituted [18]Crown‐6 Ethers: Is Flatter Better?

Abstract

The twisted lateral tetraalkyloxy ortho-terphenyl units in dibenzo[18]crown-6 ethers 1a-f were readily converted into the flat tetraalkyloxytriphenylene systems 2a-f by oxidative cyclization with FeCl(3) in nitromethane. Reactions of the latter with potassium salts gave complexes KX.2, which displayed mesomorphic properties. The aromatization increased both the clearing and melting points; the mesophase stabilities, however, were mainly influenced by the respective anions upon complexation with various potassium salts. In contrast, the alkyl chain lengths played only a secondary role. Among the potassium complexes of triphenylene-substituted crown ethers KX.2, only those with the soft anions I(-) and SCN(-) displayed mesophases with expanded phase temperature ranges of 93 degrees C and 132 degrees C (for KX.2e), respectively, as compared to the corresponding o-terphenyl-substituted crown ether complexes KI.1e (DeltaT=51 degrees C) and KSCN.1e (plastic crystal phase). Anions such as Br(-), Cl(-), and F(-) decreased the mesophase stability, and PF(6)(-) led to complete loss of the mesomorphic properties of KPF(6).2 although not for KPF(6).1. For crown ether complexes KX.2 (X=F, Cl, Br, I, BF(4), and SCN), columnar rectangular mesophases of different symmetries (c2mm, p2mg, and p2gg) were detected. In contrast to findings for the twisted o-terphenyl crown ether complexes KX.1, the complexation of the flat triphenylene crown ethers 2 with KX resulted in the formation of organogels. Characterization of the organogel of KI.2e in CH(2)Cl(2) revealed a network of fibers.

Torands Revisited: Metal Sequestration and Self‐Assembly of Cyclo‐2,9‐tris‐1,10‐phenanthroline Hexaaza Macrocycles

“…Similar observations were made previously for liquid‐crystalline crown ether derivatives and their corresponding metal complexes 60–62. To this effect, the Ag + and Pb 2+ complexes, 7 b ‐Ag and 7 b ‐Pb, respectively, were investigated by temperature‐dependent 2D‐WAXS experiments.…”

Thermotropic Ionic Liquid Crystals

“…In a similar approach, the liquid crystalline state could be generated in crown ether structures via incorporation into the ligand cavity of alkali metal cations [118,119]. For the crown-ether-derived ligands, bearing rigid lateral aryl or terphenylene subunits ( 78 , Scheme 18), the influence of the alkali metal cation, counteranion and mesogenic substituents around the ligand-metal core on the structure of liquid crystalline phases and their stability at diverse temperature conditions have been investigated [120,121,122,123,124]. …”

Synthesis, mesomorphic and gelation properties of 7-alkoxycoumarin-3-carbonyl hydrazine

“…In recent years, there has been growing interest in the rational design and synthesis of some new organic molecules that can exhibit thermotropic mesomorphic behaviours (liquid crystals, LCs) and gelate with kinds of solvents (low-molecular-mass organic gelators, LMOGs) [1][2][3][4][5][6]. Both LCs and LMOGs are organised soft materials, where hydrogen bonding, π-π stacking, van der Waals interaction, coordination interaction and other weak interactions are considered as the general driving force of the mesophase and gel formation.…”