Toward the Biaxial Nematic Phase of Low Molar Mass Thermotropic Mesogens:  Substantial Molecular Biaxiality in Covalently Linked Rod−Disk Dimers

Hunt, Jonathan J.; Date, Richard W.; Timimi, Bakir A.; Luckhurst, G. R.; Bruce, Duncan W.

doi:10.1021/ja015943q

Cited by 75 publications

(50 citation statements)

References 15 publications

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“…[38][39][40][41][42] For example, rodlike mesogens have been end-on and side-on attached to disclike mesogens. Another is disclike mesogens attached to rigid-rod backbone polymer chains.…”

Section: Introductionmentioning

confidence: 99%

Self-Assembly of Chemically Linked Rod−Disc Mesogenic Liquid Crystals

et al. 2007

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A series of new molecular discs (RDn, here n is the number of carbon atoms between the rod and disc mesogens) was synthesized via the chemical attachment of six cyanobiphenyl calamitic (rod) mesogens (R) linked to the triphenyl discotic (disc) mesogen (D) with a series of six alkyl chain linkages (n = 6-12). In this study, phase structures, transitions, and liquid crystalline (LC) behavior of the RD12 compound with 12 carbon atoms in each alkyl chain linkage between the rod and disc mesogens were investigated. Differential scanning calorimetry, polarized light microscopy, wide-angle X-ray diffraction (WAXD), and selected area electron diffraction (SAED) allowed us to identify three ordered phases below the isotropization temperature: nematic (N) LC and K1 and K2 crystalline phases. On the basis of the structural results obtained via 2D WAXD experiments on oriented samples and SAED experiments on single crystals, the K1 crystalline unit cell was determined to be triclinic with the dimensions of a = 1.36 nm, b = 1.45 nm, c = 2.11 nm, alpha = 85 degrees, beta = 100 degrees, and gamma = 50 degrees. The K2 phase was metastable with respect to the K1 phase. It also possessed a triclinic unit cell with a = 1.40 nm, b = 1.51 nm, c = 1.92 nm, alpha = 87 degrees, beta = 117 degrees, and gamma = 62 degrees. Molecular packing models for the crystalline phases were proposed on the basis of the diffraction results. In the whole range of ordered structures, it was found that RD12 molecular discs are intercalated. Both triphenyl discotic mesogens and cyanobiphenyl calamitic mesogens are completely interdigitated.

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“…[38][39][40][41][42] For example, rodlike mesogens have been end-on and side-on attached to disclike mesogens. Another is disclike mesogens attached to rigid-rod backbone polymer chains.…”

Section: Introductionmentioning

confidence: 99%

Self-Assembly of Chemically Linked Rod−Disc Mesogenic Liquid Crystals

et al. 2007

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“…However, efforts to observe a N b phase in two component melts of rod-and disklike LCs have been unsuccessful [5,7,8]. Even extravagant molecular architectures -covalently bonded disk and rod mesogens -have failed to exhibit the N b phase [9]. For a single-component fluid comprised of parallelepipeds with sufficiently large aspect ratios [ Fig.…”

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confidence: 99%

Thermotropic Biaxial Nematic Liquid Crystals

et al. 2004

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We have synthesized liquid crystal (LC) mesogens based on a nonlinear oxadiazole unit that exhibit nematic phases near 200 degrees C. Polarized microscopy and conoscopy indicate that these LCs are biaxial nematics. Unambiguous and quantitative evidence for biaxiality is achieved using 2H NMR spectroscopy. "2D powder" spectra, obtained by rotating 2H-labeled samples about an axis perpendicular to the magnetic field at approximately 200 Hz, yield phase biaxiality parameters of approximately 0.1 when coupled with rigorous and proven simulations.

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“…After the work of Fletcher and Luckhurst [162], other molecular design concepts have been explored [162,163,161,164,165,166] obtaining N u but not N b . So far, the mesogen with closest resemblance to the theoretical cartoon of joined mesogens is the one of Kouwer and Mehl [164].…”

Section: Mixturesmentioning

confidence: 99%