Liquid crystalline dimers with bent‐core mesogenic units

Achten, Remko; Koudijs, A.; Giesbers, Marcel; Marcelis, Antonius T. M.; Sudhölter, Ernst J. R.; Schroeder, Martin W.; Weißflog, W.

doi:10.1080/02678290601061330

Cited by 28 publications

(12 citation statements)

References 22 publications

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“…Such a relationship also exists for carbosilane-connected twin molecules [24,25]. In contrast, if alkylene spacers and oligo(oxyethylene) spacers are used, the formation of SmC or columnar phases is preferred [23,26]. Applying an electric field, these columnar phases do not show any current response which means these are not polar phases.…”

Section: Introductionmentioning

confidence: 81%

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Banana-calamitic dimers: unexpected mesophase behaviour by variation of the direction of ester linking groups in the bent-core unit

et al. 2010

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A five-ring bent-core unit and a phenyl benzoate moiety are linked together by means of a flexible spacer. Starting from dimers having different length of the aliphatic parts, that is the terminal alkyloxy chains and the spacer, the direction of each of the four ester connecting groups in the bent-core unit is reversed step by step. In this way thermodynamically stable polar and non-polar mesophases in unusual sequences could be obtained. For instance, a SmC s P AF -SmC ś P AF transition and the existence of two nematic phases (N, N X ) have been observed. The nematic phases of the banana-calamitic dimers exhibit unusual properties comparable to those of the nematic phases reported for some monomeric bent-core mesogens. The electric field-induced enhancement of the SmCP-SmA transition temperature of one compound proves the existence of polar clusters already in the non-polar SmA phase.

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Section: Introductionmentioning

confidence: 81%

“…In 2002 Tschierske et al prepared the first dimers of this type [22]. The SmCP phases observed for these compounds exhibit ferro-and antiferroelectric behaviour, dependent on the number of dimethylsiloxane units [22,23]. Such a relationship also exists for carbosilane-connected twin molecules [24,25].…”

Section: Introductionmentioning

confidence: 89%

Banana-calamitic dimers: unexpected mesophase behaviour by variation of the direction of ester linking groups in the bent-core unit

et al. 2010

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“…Symmetric and non-symmetric dimers composed of two bent-core units which are linked by flexible spacer of different length and chemical constitution of distinct topology have been reported by several research groups [16][17][18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Banana-calamitic Dimers: Further Variations of the Bent-core Mesogenic Unit

et al. 2014

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Banana-calamitic dimers are a topic in the field of bent-core mesogens. New materials were prepared by chemical variations at the bent-core fragment that is by a cyano group terminally attached to the bent-core fragment, by lateral substitution with a chlorine atom and methyl group, respectively, and by increasing the number of phenyl rings from five to six. The bent-core and the calamitic mesogenic moieties are connected by aliphatic spacers of different length. The materials were investigated by optical microscopy, DSC, X-ray diffraction studies and electro-optical measurements. This way nematic, smectic and various types of polar columnar phases have been characterized. The low temperature phase in a sequence of two nematic phases exhibiting different properties can be classified as a nematic twist-bend phase. Such NTB phases are only formed if a bend exists along the molecular long axes. This prerequisite can be doubly achieved in banana-calamitic dimers: by the intrinsic bend of one of the mesogenic fragments and by an odd-numbered spacer.

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“…If two bent-core moieties are terminally linked together, the parity of the spacer strongly influences the LC behaviour. Mostly, "banana phases" have been found [69][70][71][72][73][74][75]. Banana-calamitic dimers are of topical interest because "banana phases" and "calamitic phases" can exist for the same compound.…”

Section: Introductionmentioning

confidence: 99%

Photochromic azobenzene functionalised banana–calamitic dimers and trimers: mesophase behaviour and photo-orientational phenomena

et al. 2011

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Azobenzene functionalised banana-calamitic dimers and a novel type of banana-calamitic-banana trimers have been synthesised. Their thermotropic behaviour and the structure of the mesophases have been characterised by differential scanning calorimetry, polarising optical microscopy and X-ray diffractions measurements. Electro-optical studies evidence the polar properties of the smectic phases. A rare anticlinic-synclinic smectic CP (SmCP) phase transition could be proven for two of the twins upon cooling without an electric field although the molecules are not optically active. Remarkably, the phase sequence SmC a -SmC s has been observed upon cooling, the inverse sequence to that reported for non-chiral compounds up to now. A comparative study of the photochemical properties of dilute solutions and of thin films of two compounds has been performed. Irradiation with polarised ultra-violet (365 nm) and visible light (473 nm) induces a photo-orientation process of the chromophores in a direction perpendicular to the polarisation plane of the exciting light. For a trimeric compound bearing an azobenzene bridge between both bent-core mesogenic units this process is associated with cycles of the E-Z-E isomerisation of the azobenzene groups followed by rotational diffusion of molecules in the films. For a bis(azobenzene) containing dimer the E-Z isomerisation in films is strongly suppressed and the photo-induced orientation has a rotational diffusion mechanism.

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Liquid crystalline dimers with bent‐core mesogenic units

Cited by 28 publications

References 22 publications

Banana-calamitic dimers: unexpected mesophase behaviour by variation of the direction of ester linking groups in the bent-core unit

Banana-calamitic dimers: unexpected mesophase behaviour by variation of the direction of ester linking groups in the bent-core unit

Banana-calamitic Dimers: Further Variations of the Bent-core Mesogenic Unit

Photochromic azobenzene functionalised banana–calamitic dimers and trimers: mesophase behaviour and photo-orientational phenomena

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