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Study on Preparation and properties of liquid crystal compound of benzimidazole

Author: ZhangLiNa
Tutor: ChenXinBing
School: Shaanxi Normal University
Course: Materials Science
Keywords: Benzimidazole Liquid crystal Smectic mesophase Hydrogen bonding
CLC: O626.23
Type: Master's thesis
Year: 2013
Downloads: 64
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Abstract


It has been well documented that the thermotropic mesomorphase of calamitic liquid crystals is basically dependent on the molecular structure in which a slight change brings about considerable change in its properties. Efforts focused on modification of existing molecules have been proved to be an effective method to obtain novel liquid crystals. Over many years, a great number of mesogenic compounds containing heterocyclic units have been synthesized to substitute benzene or naphthalene unit as mesogenic core, such as1,3,4-oxadiazoles,1,2,3-triazoles, flavone and isoflavone, and coumarin, and interest in such structures continues to grow because the incorporation of heteroatoms (N, O and S, commonly introduced) can result in considerable changes in the corresponding mesophase type, the phase transition temperatures and other properties of the mesogens due to their much larger polarity than carbon or the shape change of the molecule. Imidazole derivatives possess kinds of applications especially in medicinal chemistry. However, to the best of our knowledge, few reports on liquid crystals containing terminal benzimidazole group is available in the literature. The scientific interest in the synthesis and the better understanding the structure-property correlations of benzimidazole-based liquid crystals has prompted us to design and synthesize three series of2-(4’-alkoxybiphenyl-4-yl)-1H-benzimidazole derivatives (nM-X). The main contents and results are as follows:1. Design and synthesize three series of2-(4’-alkoxybiphenyl-4-yl)-1H-benzimidazole derivatives (nM-X), where5-nitrobenzimidazole (nM-N series), benzimidazole (nM-H series) or5-methylbenzimidazole (nM-M series) units are appended to the terminal position of the molecule. The HPLC purities is higher than98%. Structures of all compounds were confirmed by1H NMR,13C NMR, IR, ESI-MS and EA.2. Thermal behavior of the target compounds (nM-X) was studied by TGA, DSC and POM. TGA measurements showed that decomposition temperature of all compounds was greater than300℃; The results of DSC and POM showed that all the compounds exhibited enantiotropic mesophases for a carbon number in the alkoxy chain from6to16, where the mesophase ranges were14～91℃and17～99℃during heating and cooling processes for the nM-N compounds,7～25℃and8～49℃for the nM-H compounds and48～81℃and52～85℃for the nM-M compounds, respectively.3. Mesophase of nM-X was confirmed by POM, DSC and XRD. The result of Temperature-dependent FT-IR spectroscopy showed that the formation of liquid crystal phase was mainly attributed to lateral hydrogen bonding interactions between molecules at benzimidazole ring the end.4. The effect of the length of alkoxy chain on mesomorphic properties was discussed. The nM-N and nM-M exhibited a much wider mesophase range whether during heating or cooling process than the corresponding nM-H series, which indicated that the substituent in the benzimidazole moiety was helpful in increasing the mesophase stability.

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CLC: > Mathematical sciences and chemical > Chemistry > Organic Chemistry > Heterocyclic compounds > Containing five pairs or more different atoms of heterocyclic > Between the two nitrogen -mao ( imidazole) and its derivatives
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