Discotic liquid crystal is a kind of new organic semiconductors, the discotic dimers can display different self-organizing behaviours. Six functionalized triphenylene discotic monomers were prepared, and then Pd-catalyzed homo-coupling reaction was used for the preparation of symmetrical discotic liquid crystal dimers, (RO)₅C₁₈H₆(O₂CC₆H₄C≡C—C≡CC₆H₄CO₂)C₁₈H₆(OR)₅ (R＝C_nH_2n＋1, n＝4～9), for which two triphenylene discogens was connected via a rigid spacer. The purity and structure of the new compounds was confirmed by using ¹H NMR, IR and high resolution mass. Thermal gravimetry analysis (TGA) results show that the dimers have good thermal stability, beginning to decompose at 370 ℃. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) results display that the monomers and dimers exhibit columnar mesophases. The dimers display wide mesophase range and are room temperature liquid crystals. The clearing points of dimers increase with the lengthening of peripheral alkyl chain, while the monomers show opposite trend.

Key words: triphenylene, Pd-catalyzed homo-coupling, discotic liquid crystal dimer, columnar mesophase, room temperature discogen