Novel half-disk mesogens of general structure 6,7,10,11-tetrakis(alkoxy)triphenylene-1,4-dione were synthesized and their phases characterized by polarized microscopy, DSC and x-ray diffraction. These compds. form hexagonal columnar mesophases upon heating, despite their half-disk mol. shapes. X-ray diffraction suggests that within the mesophases a dimeric mesogenic subunit exists, driven by dipolar forces, in which the mols. are oriented antiparallel to one another. Such a dimer is approx. disk-shaped, and may explain the formation of columnar phases by these half-disk mols. [on SciFinder(R)]