Synthesis and Mesomorphism of Triphenylene Discotic Liquid Crystals Containing Fluorinated Chains

Abstract

In this article, we synthesized a series of triphenylene discotic liquid crystals (TPDLCs) containing up to three fluorinated ester chains: C₁₈H₆(OC_nH_2n+1)_6−m(O₂CC₂H₄C₆F₁₃)_m (n = 4–9, 11; m = 1–3); as well as their corresponding non-fluorinated TPDLCs: C₁₈H₆(OC_nH_2n+1)₅(O₂CC₈H₁₇) (n = 4–9, 11), 2,7-C₁₈H₆(OC₅H₁₁)₄(O₂CC₈H₁₇)₂, and C₁₈H₆(OC₉H₁₉)₃(O₂CC₈H₁₇)_3. The compounds were characterized by using nuclear magnetic resonance (NMR), elemental analysis, and mass. Thermal gravimetry analysis (TGA) showed that the FTPDLCs were thermally stable until 300°C. Differential scanning calorimerty (DSC) and polarized optical microscopy (POM) investigations of the mesomorphism found that the FTPDLCs exhibited enantiotropic hexagonal columnar mesophase (Col_h) and had much higher clear points than the corresponding hexaalkoxytriphenylenes, C₁₈H₆(OR)₆. Noticeably, semi-quantitative studies showed that the number of fluorinated ester chains on the triphenylene core was directly proportional to FTPDLCs' clearing points and the order of hexagonal columnar mesophases. In addition, FTPDLCs' mesomorphism was found to be affected by molecular symmetry and by the relative length between the semi-fluorinated chains and the alkoxy chains. Most importantly, we further proved that the mesomorphism of TPDLCs could be better improved through introducing fluorinated ester chains than the ether chains as reported previously.

Keywords:

• Triphenylene
• Discotic liquid crystals
• Semi-fluorinated ester peripheral chains
• Molecular symmetry

ACKNOWLEDGMENT

This work was supported by the National Natural Science Foundation of China (Nos. 50973076, 20872104, and 50811140156), Scientific Research Fund of Sichuan Normal University (08QNL04).