A series of triphenylene-based discotic dimers have been synthesized, each of the triphenylene nuclei bears five b-OC 4 H 9 substituents, which are linked through the remaining b-positions by a flexible O(CH 2 ) n O polymethylene chain (n ¼ 2-12). Their chemical structures were confirmed by proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, high-resolution mass spectrometry and elemental analysis. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. It was found that these dimers for which n > 4 formed a highly ordered columnar plastic phase and some of them (n ¼ 6, 7, 10, 11, and 12) exhibited multiple mesophases. This is the first time that the rectangular columnar plastic phase was defined by us as a novel liquid crystal phase of compound 4d (n ¼ 5). The introduction of a single interconnecting chain between adjacent molecules does not significantly perturb the formation of a columnar plastic phase but enriches the mesophases of discotic molecules and hinders the crystallization; the mesophases of 4e-k (n ¼ 6-12) can be supercooled into a glass state in which the self-assembly columnar structures are retained.

A series of dibenzocoronene tetracarboxdiimide derivatives decorated with alkyl swallow-tail and alkoxy moieties were synthesized, and their structures were characterized. 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an effective oxidant was first used in the benzannulation of perylene diimides with the almost quantitative yield. The thermotropic behavior was investigated using differential scanning calorimetry (DSC) and polarization optical microscopy (POM). The introduction of alkyl swallow-tail and alkoxy substituents facilitates thermotropic liquid crystalline behavior. The branching site of alkyl swallow-tail units at the α position and the longer alkoxy chains played a similar role in lowering the mesophase transition as well as isotropization transition temperatures. The UV-vis absorption spectra of all compounds appeared as absorption in 425-600 nm region, and POM images of certain compounds exhibited characteristic columnar hexagonal (Col(h)) packing and readily self-assembled into a homeotropic alignment toward the substrate.

The perfect spacer length and substitution positions were foundviasystematical study on triphenylene-based discotic liquid crystalline polyethers.

A clear structure-property relationship was revealed in a series of triphenylene-based dimers, which contained two triphenylene nuclei each bearing five β-OC4H9 substituents and are linked through a flexible O(CH2)nO polymethylene chain (n=6-12). Dimers with the linkage close to twice the length of the free side chains (n=8, 9) exhibited a single Colhp phase, while others with the linkage shorter (n=6, 7) or longer (n=10, 11, 12) showed multiphase behaviors with a transition from the Colhp phase to Colh phase; hole mobilities of Colhp phases reached 1.4×10(-2) cm2 V(-1) s(-1) in the dimer for which the linkage is exactly twice the length of the free side chains (n=8), and decreased regularly both with linkage length becoming shorter or longer. This modulation of phase behaviors and charge carrier mobilities was demonstrated to be generated by various steric perturbations introduced by linkages with different lengths, which result in different degrees of lateral fluctuations of discotic moieties in the columns.