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

Abstract

New liquid crystals having a non-conventional structure have been synthesised from a six-armed cyclotriphosphazene core, [N(3) P(3) (OC(6) H(4) OH-4)(6) ], which was condensed with polycatenar acids. Reactions were monitored by (31) P{(1) H} and (1) H NMR spectroscopy and the chemical structure of the resulting materials was confirmed by different spectroscopic techniques and mass spectrometry (MALDI-TOF). Results were in accordance with monodisperse, fully functionalised cyclotriphosphazenes. Thermal and mesomorphic properties were studied by optical microscopy, differential scanning calorimetry and X-ray diffraction. All of the synthesised phosphazenes, substituted with benzyl ether chains, show a high thermal stability and exhibit mesomorphic properties, which depend on the number and type of alkyl terminal chains located at the periphery of the mesogens. Mesomorphic properties range from Col(h) for cph-A1 and cph-A2 to a cubic phase detected for cph-A3, which has the larger number of alkyl chains. Furthermore, helical order was detected on X-ray data of cph-A2, which has chiral branched chains. Circular dichroism spectra of annealed films at mesophase temperature show a signal attributed to the chiral helical arrangement of the mesogenic chromophores.

Supermolecular Columnar Liquid‐Crystalline Phosphorus Dendrimers Decorated with Sulfonamide Derivatives

“…Natural homeotropic textures are not unusual for hexagonal columnar liquid crystals, and previous works have unequivocally shown an absence of birefringence in some hexagonal columnar dendromesogens. [12] DSC thermograms helped to confirm the mesomorphic behavior of most of the macromolecules, although it was impossible to accurately determine the clearing temperatures for the highest generation (Gc 4 ) dendrimers. In these cases, the clearing temperature was estimated from observations between crossed polarizers after mechanical treatment of the sample.…”

“…[9,10] Nevertheless, some of us have reported several series of unconventional mesogens derived from the cyclotriphosphazene ring, which can bear mesogenic units directly attached to the easily functionalized phosphorus atoms. [11,12] In those series, reaction of hydroquinone with hexachlorocyclotriphosphazene, followed by esterification of the peripheral hydroxyl groups with mono-or polycatenar benzoic acid derivatives, allowed the preparation of new liquid-crystalline compounds. Their mesomorphic properties were found to depend on a suitable volume balance between the rigid core and the alkyl chains on the mesogenic groups, and the resulting behavior ranged from calamitic, to discotic, to cubic mesomorphism with increasing number of alkyl chains.…”

“…Their mesomorphic properties were found to depend on a suitable volume balance between the rigid core and the alkyl chains on the mesogenic groups, and the resulting behavior ranged from calamitic, to discotic, to cubic mesomorphism with increasing number of alkyl chains. [11,12] Following a similar approach, a family of dendrimers up to the second generation was prepared, containing cyclotriphosphazene as a central rigid core and dendrons derived from 2,2-bis(hydroxymethyl)propionic acid, functionalized on their surface with mono-and polycatenar pro-mesogenic units. [10] Caminade and Majoral have described a well-known family of phosphorus dendrimers, poly-(phosphorhydrazone) dendrimers (PPH), based on this type of rigid 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].…”