Different disk structures in the hexagonal columnar mesophases of 2,3-dicyano-6,7,10,11-tetraalkoxy-1,4-diazatriphenylenes and 2,3-dicyano-6,7,10,11-tetraalkoxytriphenylenes

We have synthesized two series of C-2v symmetric discotic liquid crystals of 2,3-dicyano-6,7,10,11-tetraalkoxy-1,4-diazatriphenylene [referred to as (CnO)(4)DADCT (1); n=8, 10, 12, 14] and 2,3-dicyano-6,7,10,11- tetraalkoxytriphenylene [ referred to as (CnO)(4)DCT (2); n=8, 10, 12, 14]. Polarizing microscopic observations, differential scanning calorimetry and temperature-dependent X-ray diffraction studies revealed that each of the (CnO)(4)DADCT (1) and (CnO)(4)DCT (2) derivatives exhibits a hexagonal ordered columnar (Col(ho)) mesophase, and that each of the (CnO)(4)DADCT (1) derivatives forms monomer disks in the Col(ho) mesophase, whereas each of the (CnO)(4)DCT (2) derivatives forms dimer disks in the Col(ho) mesophase. It is very interesting that the different disk structures may originate from the kind of atoms at the alpha-position to the CN groups in (CnO)(4)DADCT (1) and (CnO)(4)DCT (2).