13478-57-4Relevant academic research and scientific papers
Javelin-, hockey stick-, and boomerang-shaped liquid crystals. Structural variations on p-quinquephenyl
Dingemans, Theo J.,Murthy, N. Sanjeeva,Samulski, Edward T.
, p. 8845 - 8860 (2007/10/03)
The ramifications of changing molecular geometry in a series of all-aromatic liquid crystals derived from p-quinquephenyl are reported. Substituting heterocyclic rings such as thiophene, oxadiazole, oxazole, or 1,3-phenylene into the p-quinquephenylene core affects molecular shape changes via the substituent's exocyclic bond angle. In general, we found that introducing nonlinearity into molecules depresses the melting transition temperature. The symmetric (boomerang-shaped) molecules, 2,5-bisbiphenyl-4-yl-1,3,4-oxadiazole, 2,5-bisbiphenyl-4-yl-oxazole, and 1,3-bisbiphenyl-4-yl-benzene, melt into isotropic phases showing small monotropic mesophases. By contrast, the asymmetric (hockey stick-shaped) mesogens, 2-terphenyl-4-yl-5-phenyl thiophene and 2-terphenyl-4-yl-5-phenyl-1,3,4-oxadiazole, exhibit more stable enantiotropic liquid crystalline phases. The hockey stick-shaped mesogens exhibit a smectic phase as well as a nematic phase. High-temperature X-ray determination of the smectic layer spacing gives an unambiguous picture of interdigitated, bilayerlike supramolecular architecture in the smectic phase. There are associated changes in the mesogen's electrostatic profile when a heterocycle is introduced into the quinquiphenylene framework (e.g., conjugation is perturbed). Our findings suggest that steric packing considerations dominate the phase preferences (nematic versus smectic phases). However, electronic considerations (conjugation) appear to control the range of mesomorphism in this new family of nonlinear liquid crystals.
Studies of Polyphenyls and Polyphenylenes. II. The Synthesis and Physical Properties of Polyphenyls Containing Para Linkage
Ozasa, Shigeru,Hatada, Noriko,Fujioka, Yasuhiro,Ibuki, Eiichi
, p. 2610 - 2617 (2007/10/02)
Twelwe linear polyphenyls, including quinque- to octiphenyl, were synthesized by the Ullmann cross-coupling reaction of iodobiphenyl with diiodobenzene or iodoterphenyl.Ultraviolet spectral studies of the polyphenyls indicated that the positions of the K-bands above ca.260 nm, regardless of the presence of o- or m-phenylene unit(s), may be considered to be an indication of the approximate number of consecutive p-phenylene units.Infrared studies also showed that the locations of strong or medium bands in the 815-850 cm-1 region may give the same information.The HMO calculations of the longest wavelength absorption bands of twenty-four polyphenyls were carried out.A comparison between the calculated and observed wavelengths gave rather good agreement, except in the cases of two compounds.The signals of the proton magnetic resonanse spectra of eighteen polyphenyls were assigned tentatively.The correlations between the arrangement of the benzene rings and the spectral patterns are discussed.
