Heterocyclic 1,2,4-triazoles as calamitic mesogens

Su, Chaochin; Lee, Li Xiang; Yu, Shang Hsun; Shih, Ying Kai; Su, Jen Chun; Li, Fu Joun; Lai, Chung K.

doi:10.1080/02678290410001690429

Cited by 14 publications

(2 citation statements)

References 18 publications

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“…For example, bent phasmidic molecules bearing three alkyloxy chains at both terminal phenyl rings (see Scheme 1a) often form columnar phases, as observed for correspondingly substituted benzoic anhydrides, gallic esters of 4,5-dinitrobenzcatechol, 3,5-diphenyl-1,2,4-triazoles, 3,5-distyrylpyridines, and furthermore. [11][12][13][14][15][16] The molecular organisation can be modified by hydrogen bonding, as found for example for related urea derivatives and amido group containing mesogens. 17,18 Furthermore, the strong tendency towards microsegregation is well-known for molecules bearing perfluoroalkyl chains.…”

Section: Introductionmentioning

confidence: 99%

Unexpected liquid crystalline behaviour of three-ring bent-core mesogens: bis(4-subst.-phenyl) 2-methyl-iso-phthalates

et al. 2012

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Three-ring bent-core bis(4-subst.-phenyl) 2-methyl-iso-phthalates exhibiting nematic, SmA and SmC phases are reported. The occurring mesophases have been identified by their optical textures and X-ray diffraction measurements which give also geometrical structural parameters like layer spacing and molecular tilt. Quantum chemical calculations on single molecules and X-ray structure analysis in the crystalline state indicate wide opening angles (about 155 ) of the molecular legs due to the lateral methyl group in position 2 of the central phenyl ring. However solid state NMR spectroscopy in the liquid crystalline phases finds stronger molecular bending (bending angle to be about 138 in the SmA and about 146 in the nematic phase). Dielectric and SHG measurements give evidence that in the SmA phase a polar structure can be induced by application of an electric field which disappears in the isotropic liquid phase. The electric field not only leads to a slight textural change even in the SmA phase but also polar-type electric current response (P S about 200 nC cm À2 ) is observed. This unusual electrooptical behaviour is discussed on the basis of the orientation of polar clusters formed by the bent molecules. In the paper we not only attempt to characterize the mesophases and to describe their physical properties, but we also show that these types of molecules represent the borderline between bent-shaped and calamitic liquid crystals.

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Section: Introductionmentioning

confidence: 99%

Unexpected liquid crystalline behaviour of three-ring bent-core mesogens: bis(4-subst.-phenyl) 2-methyl-iso-phthalates

et al. 2012

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“…The situation is changed, however, if additional effects influence the molecular interactions. For example, microsegregation caused by terminal perfluoroalkyl chains [11] or more than one alkyl chain at the terminal phenyl rings leading to bent-core phasmidic mesogens can result in smectic and columnar phases [12][13][14][15][16][17]. The influence of hydrogen bonding should additionally be mentioned [18,19].…”

Section: Resultsmentioning

confidence: 99%

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Weißflog

2011

Liquid Crystals

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Banana-shaped liquid crystals are a topic in the field of liquid crystals; for some reviews see, for example, [1-3]. Therefore, new relationships between the molecular structure and the mesophase behaviour are of high interest. Since the first report on bananashaped liquid crystals in 1996 one of the basic questions has been 'What is the size of the bent core?' [4]. Also 'How many aromatic rings are necessary to form so-called banana phases?' For a long time it seemed that at least five phenyl units were needed to form banana phases exhibiting spontaneous polarisation. In the meantime, different groups reported that bent-core four-ring compounds can also show mesophases exhibiting spontaneous or field-induced polarity [5, 6].

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Laterally Alkyl‐ and Aryl‐Substituted, Swallow‐Tailed, and Polycatenar Mesogens: Structural Features and Functionalities

Weißflog

2014

Handbook of Liquid Crystals

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Long‐chain groups additionally attached to calamitic mesogens change the shape of the molecules and, therefore, their attractive and repulsive interactions. While compounds bearing lateral alkyl groups mostly exhibit nematic phases, lateral substitution with aryl‐containing groups means a qualitative jump by special packing in layer structures. Polycatenar mesogens can be wedge or dumbbell shaped depending on the number and positions of hydrocarbon chains at one or both terminal positions. Phasmidic and double‐swallow‐tailed mesogens are not able to exhibit smectic A phases for steric reasons, which can be induced, however, in mixtures with small rodlike molecules. Lateral alkyl chains attached to bent‐core mesogens reduce the tendency to form polar switchable layer phases, whereas polycatenar bent molecules form columnar structures. Equipping the molecules under discussion with functional groups in any ω‐standing position allows the lateral or terminal connection of mesogens, for example, to dendrimers, polymers, or metallic surfaces such as gold. In general, increasing the number of aliphatic chains often decreases melting points, increases solubility, and, therefore, allows better processability of functional materials.

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Heterocyclic 1,2,4-triazoles as calamitic mesogens

Cited by 14 publications

References 18 publications

Unexpected liquid crystalline behaviour of three-ring bent-core mesogens: bis(4-subst.-phenyl) 2-methyl-iso-phthalates

Unexpected liquid crystalline behaviour of three-ring bent-core mesogens: bis(4-subst.-phenyl) 2-methyl-iso-phthalates

Comment on the paper

Laterally Alkyl‐ and Aryl‐Substituted, Swallow‐Tailed, and Polycatenar Mesogens: Structural Features and Functionalities

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