Synthesis and mesomorphism of diacetylene-bridged triphenylene discotic liquid crystal dimers

Abstract

m -C≡≡ C-] 2 , 8(m), (m = 1, 3) by Eglinton coupling reaction. The thermotropic liquid crystal properties were studied by differential scanning calorimetry and polarized optical microscopy. The results are showed as follows: the length of peripheral alkyl chains of triphenylene influenced properties of liquid crystal dimers; dimers 3(n) (n = 5-8) and 6 had glass columnar phase, and no crystallization was observed above −50℃ for all the triphenylene dimers; compared with 3(6), 6 showed higher molecular symmetry, more stable columnar mesophase and wider mesophase range. The connecting group, length and rigidity of spacer had important influence on the mesomorphism of diacetylene-bridged triphenylene discotic liquid crystal dimers.triphenylene, discotic liquid crystal, Eglinton coupling reaction, liquid crystal dimer, glass columnar phase Liquid crystal dimers are a type of molecule which contain two identical or different mesogenic groups linked via a spacer. Their physical properties are different from those of conventional low molecular mass liquid crystals. They show a variety of mesophases [1][2][3][4][5][6] and some of liquid crystal dimers display properties of polymers, such as glass transition behavior [7][8][9] . So they can serve as ideal model compounds in liquid crystal polymer investigation and have received considerable attention. Rod-like liquid crystal dimers have been well studied and their structure-property relationships have been elucidated [10] . By contrast, discotic liquid crystals (DLCs) have comparatively short history. Thus, further exploration of the synthesis, characterization and structure-property relationships of DLC dimers, oligomers and polymers is necessary.Triphenylene derivatives are important family members of DLCs. They can self-assemble into highly ordered hexagonal columnar (Col ho ) mesophase and possess high mobility of charges and energy [11] . Moreover, triphenylene DLCs can be easily synthesized and purified, showing plenty of structural variation and fine thermal and chemical stability [12,13] . They have been applied as one-dimensional conductors [14] , photoconductors [15] , and light-emitting diodes [16] . In recent years, triphenylene DLC dimers, oligomers and polymers have attracted increasing attention [17][18][19][20][21][22][23][24] . The dynamics of discogens, such as rotation around the column axes, fluctuation in the column, and slippage out of column, has been partially inhibited by connecting two triphenylene mesogens via a spacer. Thus, the dimers show more ordered and stable Col mesophase and im-

W-shaped liquid crystalline dimers

“…Calamitic LC dimers and oligomers have been formerly investigated as convenient models to study the correlation between the molecular structure and mesophase formation for liquid crystalline main-chain and side-chain polymers. [9][10][11][12][13][14] Research in this eld is attracting increasing interest because the variability in the design and molecular structures of these materials is almost immense and as the mesomorphic properties of LC dimers are complex and different from the corresponding monomers. Generally, calamitic, discotic, and bent-core mesogens have been applied to create dimers of various shapes, such as H-, [15][16][17] T-shaped 18,19 and disc-shaped, 20 but most of the dimers are derived from calamitic and bent-core mesogens.…”

Synthesis of functionalized triphenylene discotic liquid crystals and the influence of unsaturated periphery on mesomorphism

“…The mesomorphism engineering of triphenylene DLCs covers the connecting group between core and periphery, the length of periphery, the combination of hydrophilic and hydrophobic chains, hydrogen-bond forming groups [26][27][28][29], fluorinated chain [30][31][32], oligomerization [33,34] and polymerization [35].…”

Synthesis of disk-rod-disk liquid crystal trimers by using click chemistry

“…These features have made triphenylene discotic liquid crystals as prominent candidates as one-dimensional conductors and semiconductors [2][3][4][5]. Several triphenylene discotic liquid crystal dimers, oligomers and polymers have been synthesized [6][7][8]. Triphenylene discotic liquid crystal trimers are molecules containing three mesogenic units joined by two flexible spacers [9][10][11][12].…”