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Two series of triphenylene-based dimers both having a central fluoromethylene spacer of four or six carbon atoms and ester or amide linkages were synthesised and their phase behaviour investigated. All the synthesised dimers are room-temperature discotic liquid crystals and exhibit hexagonal columnar mesophases that supercool into a stable anisotropic columnar glass. The length of the fluoromethylene spacer has a minor effect on the phase transition temperatures of these dimers. However, dimers  1a  and  2a  with a (CF 2 ) 4  spacer exhibit approximately 40°C higher clearing points and wider mesomorphic phase ranges compared with their hydrocarbon analogs  1c  and  2c  with a (CH 2 ) 4  spacer respectively. Compared to the corresponding ester-linked dimers  1a-c , three amide-linked dimers  2a-c  exhibit 20°C higher clearing points upon cooling. The observation indicates not only that the introduction of the fluoromethylene spacer stabilised the mesophase in these discotic dimers, but also that the two interactions have synergistic effects on columnar packing in this system. Moreover, only amide-linked dimers exhibit good gelation property in a mixture of toluene and petrol ether, with a lower critical gelation concentration of 1.5 wt/vol%, thus indicating that gel formation occurred under the collaboration of hydrogen bonding and intrinsic π interactions in these dimers.

Room-temperature triphenylene-based discotic liquid crystal dimers: effects of amide linkage and central fluoromethylene spacer