Polycatenar liquid crystals with long rigid aromatic cores: a review of recent works

Polycatenar Mesogens with Various Degree of Flexibility of Molecular Structure

“…The design of new types of mesogens has been an important topic of liquid crystal (LC) research since their discovery. Mesogenic molecules form a nearly unlimited variety of structures, the basic factors governing their self‐assembling are minimizing the excluded volume and maximizing the attractive interactions between molecules . The spectrum of anisotropic molecular geometries determining the types of a LC phases is constantly extended.…”

Mesomorphic property of 2,5-dibenzoyloxy-, 5-benzoylamino-2-benzoyloxy-, and 2,5-dibenzoylamino-tropones with mono-, di-, and tri-alkoxyl groups on the benzoyl groups and their benzenoid derivatives

“…When the number of the side chains is increased, the mesomorphic property is changed. An elongated, strictly linear, and mostly polyaromatic core, which is terminated by three to six flexible chains, is called a polycatenar mesogen [2,3]. The increase in the number of chains disturbs the organisation of the rigid cores in infinite layers and gives rise to a change of the mesophase type from smectic to columnar via cubic phases.…”

“…In the columnar phases the rod-like cores are organised in columns and the disruption of the layers induces ribbons, which are surrounded by the fluid chains. It was also recognised that in order to keep the mesomorphic properties in such polycatenar mesogens, the core length has to be increased as the number of the side chains is increased [2,3]. Hence, it was generally reported that four rings (k ¼ 2) are the minimum number of rings in the rigid cores of tetracatenar mesogens (mþn ¼ 2) and at least five rings (k ¼ 3) are required in penta-(mþn ¼ 3) and hexacatenar (mþn ¼ 4) mesogens to induce columnar mesophases.…”

“…Hence, it was generally reported that four rings (k ¼ 2) are the minimum number of rings in the rigid cores of tetracatenar mesogens (mþn ¼ 2) and at least five rings (k ¼ 3) are required in penta-(mþn ¼ 3) and hexacatenar (mþn ¼ 4) mesogens to induce columnar mesophases. Penta-and hexa-catenar mesogens with only three (k ¼ 1) or four (k ¼ 2) rings can also form liquid crystalline phases, but they show exclusively nematic and in a few cases also smectic phases [2,3]. When additional structural modifications such as introduction of hydrogen bonding groups, however, were added into molecules, they are able to form columnar phases although they have only a two-ring core structure as shown in Scheme 1 [4][5][6].…”

“…In this paper, we synthesise 2,5-dibenzoyloxytropones (1)(2)(3), 5-benzoylamino-2-benzoyloxytropones (4)(5)(6), and 2,5-dibenzoylaminotropones (7)(8)(9) with mono-, di-, and tri-alkoxy groups on the benzoyl group and the corresponding benzenoids (10)(11)(12)(13)(14)(15)(16)(17)(18) to discuss the difference in mesomorphic properties depending on the core structures as well as the connecting groups.…”