According to our experimental studies for the triphenylene derivatives containing amide group with structure of C₁₈H₆(OC₅H₁₁)₃(OCH₂CONHC₄H₉)₃, the symmetrical compounds exhibit higher clearing points and more orderred hexagonal columnar mesophase than their corresponding asymmetrical ones; and also than their corresponding symmetrical compounds containing ester group. To investigate both the hy-drogen bonding and the ordering in the symmetrical and asymmetrical triphenylene discotic liquid crystals, quantum chemical ONIOM (B3LYP(6-31G(d,p)∶UFF) calculations were performed on C₁₈H₆(OC₂H₅)₃(OCH₂CONHCH₃)₃ and C₁₈H₆(OC₂H₅)₃(OCH₂COOCH₃)₃. In the optimized structures of the dimers, the distances between the p-p stacked triphenylene cores are calculated to be about 0.35 nm, in good agreement with the experimental X-ray result. A C＝O…H—N hydrogen bond is formed between two triphenylene derivatives containing amide group, which are optimized at r(N—H…O)＝0.301 nm, a near-optimum length for such an H-bond. The results show that, for compounds containing amide group, the symmetrical compounds have bigger interaction energy and higher rotation energy barrier than their correcponding asymmetrical ones due to more H-bonds formation for the former. And the compounds containing amide group have bigger interac-tion energy and higher rotation energy barrier than ones containing ester group due to the formation of H-bonds for the former. We predict a significant increase in the charge mobility when going from C₁₈H₆(OC₅H₁₁)₃(OCH₂CONHC₄H₉)₃ to C₁₈H₆(OC₅H₁₁)₃(OC₃H₆CONHC₄H₉)₃ because the rotational angle betwee two adjacent discs in the stack of the latter by optimizing is of 10.1°, which is much less than that of the former 42.6°.

Key words: triphenylene, discotic liquid crystal, intermolecular hydrogen bonding, ONIOM calculation