Columnar Mesomorphic Organizations in Cyclotriphosphazenes

Abstract

A synthetic strategy has been developed to prepare cyclotriphosphazenes that bear polycatenar aromatic esters as promesogenic units linked to phosphorus atoms. The microsegregation of the rigid and flexible parts of the system and the space-filling properties are the driving forces that determine the kind of mesomorphism exhibited by the organocyclotriphosphazenes. Mesogenic units that contain only one terminal alkyl chain give rise to calamitic mesomorphism, since the molecules are arranged to give a cylindrical superstructure with the aromatic promesogenic cores elongated in a manner approximately perpendicular to the cyclotriphosphazene ring. On the other hand, mesogenic units that contain three long terminal chains exhibit columnar mesophases. In this case, a discotic structure consisting of promesogenic cores arranged approximately parallel to the cyclotriphosphazene ring can explain the columnar organization. The X-ray diffraction patterns corresponding to the Col(h) mesophase of the cyclotriphosphazene with dodecyloxy chains (8) indicate the presence of helical ordering, which was confirmed for a homologous compound bearing stereogenic centers on two of the terminal chains (11). All of the synthesized phosphazenes show a high thermal stability.

Diskotische Flüssigkristalle: Von der maßgeschneiderten Synthese zur Kunststoffelektronik

“…C 3 -symmetrische Triazine 81 wurden durch die Reaktion von Cyanurchlorid (79 a) mit dem Biphenylderivat 80 erhalten (Schema 32). [186] [189] Vor kurzem berichteten Oriol und Serrano über die Cyclotriphosphazene 88 (Schema 34), äußerst interessante Phosphoranaloga von Triazinen, [190] deren columnare Mesophasen sogar bei tiefen Temperaturen stabil sind. Die Phosphazene sind erfolgversprechend wegen ihrer vielseitigen Einsatzmöglichkeiten für Synthesen, bemerkenswerten chemischen Stabilität, optischen Transparenz vom nahen Infrarot bis in den ultravioletten Bereich (190-210 nm) sowie ihrer geringen Entzündbarkeit.…”

Supermolecular Liquid Crystals with a Six‐Armed Cyclotriphosphazene Core: From Columnar to Cubic Phases

“…[10] Calamitic mesomorphism was previously reported on cyclotriphosphazenes [11] and this behaviour was explained in terms of a model consisting of mesogenic units arranged approximately perpendicular to the cyclotriphosphazene ring. [12,13] We have also recently contributed to this area by reporting how the liquid-crystalline properties of these non-conventional mesogens strongly depend on the number of terminal alkyl chains in the promesogenic group. Thus, we achieved the first cyclotriphosphazenes with columnar mesomorphism by directly linking polycatenar promesogenic units to the central inorganic core.…”

Liquid Crystalline Cyclotetraphosphazene

“…Molecular shape is an important factor in the formation of liquid crystal molecules. Generally, mesogenic units having one terminal chain on the aromatic ring gives rise to calamitic mesomorphism, whereas the presence of a large number of terminal chains on the aromatic ring causes the molecule to adopt a discotic structure [3,4,14,15]. Calamitic mesomorphism has been reported previously for cyclophosphazene derivatives and this behaviour was explained in terms of a model consisting of mesogenic units arranged approximately perpendicular to the cyclophosphazene ring [5][6][7][8][9][10][11][12][13].…”

“…In addition, in the field of liquid crystals, cyclotriphosphazene (trimer) and cyclotetraphosphazene (tetramer) (Figure 1) have been studied. Some trimeric derivatives showed liquid crystallinity [3][4][5][6][7][8][9][10][11][12][13][14][15]. Mesomorphic behaviour of tetramer was studied by Moriya et al, and some phase transition was seen for octacis-[4'-(4-octyloxy) biphenoxy] cyclotetraphosphazene and octacis-{[4-[N-(4' heptylyloxphenyl)iminomethyl]phenoxy]}cyclotetraphos-phazene [16].…”