Dimesogenic compounds consisting of cholesterol and fluorinated azobenzene moieties: dependence of liquid crystal properties on spacer length and fluorination of the terminal tail

Abstract

The liquid crystalline (LC) properties of two series of non-symmetric dimesogenic compounds consisting of cholesterol and ring-fluorinated azobenzene mesogenic moieties interconnected by v-oxyalkanoyl spacers of varying length are compared; one series (F-AOC-n) has the octyloxy tail attached to the fluorinated azobenzene mesogen unit while the other (F-AOCF-n) has the perfluoroheptylmethyloxy tail. In general, compounds with the fluorinated alkoxy tail exhibited a mesophase over a much wider temperature range than those with the alkoxy tail. On the other hand, the F-AOC-n series exhibited a greater variety of mesophases: TGB (twisted grain boundary), chiral smectic C (S C *), antiphase smectic A (S A ˜), cholesteric (N*) and solid state smectic (S X ) phases were observed depending on the length of the central spacer, whereas the F-AOCF-n series favored the formation of only the S A phase with the N* phase completely suppressed. Both series showed an odd-even dependence of the isotropization temperature on the spacer length.

Mesomorphic chiral non‐symmetrical dimers: synthesis and characterization

“…However, in the context of smectic A (SmA) behaviour and its structural (periodicity) modification in such dimers, some hints are available. An aromatic core possessing either a chiral tail [17,19] or perfluorinated tail seems to favour the formation of the SmA phase [9,10,20] solely. Furthermore, the fascinating structural variations of the SmA phase depend on the relative lengths of the spacer and terminal chains as well as on the nature of the aromatic core to some extent.…”

Fluorinated liquid crystalline dendrimers

“…This type of LC organisation was identified as a modulated smectic A phase (SmÃ). These modulated smectic mesophases had been previously described for low-molecular-weight mesogens bearing fluorinated terminal chains [54] as well as for some non-fluorinated codendrimers. [55,56] Similarly to the previously described codendrimers that self-assembled in a frustrated SmA + phase, the authors attributed the presence of this modulated smectic A phase (SmÃ) to the segregation produced between semifluorinated and perhydrogenated chains.…”

Synthesis and mesomorphic properties of chiral nematic liquid crystals based on cholesterol

“…[1][2][3] Many liquid crystalline compounds consisting of a cholesteryl ester unit as a chiral segment joined to different mesogenic moieties such as benzoate ester, Schiff's base, azobenzene, biphenyl, tolane, etc., through flexible spacers, have been synthesised and extensively studied. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Their liquid crystalline properties are affected by spacer length and polarity, the length of the terminal group attached to the aromatic rings, as well as the type of linking group between the spacer and mesogenic units, such as ethers and esters. They have shown interesting mesomorphic phase behaviour including SmA phases, TGB phases, blue phases and the N* mesophases.…”