Columnar discotic carboxylic esters of 2-hydroxy-3,6,7,10,11-penta(1-pentyloxy)triphenylene, characterized by a variety of functional groups, were prepared with the purpose of studying the effects of the substituents on the mesophase behaviour. Bulky substituents and polar substituents were found to destabilize the columnar mesophase. The clearing temperature is lowered and the melting point of the crystalline phase, as well as the tendency to crystallize from the mesophase, is increased. Specific substituents cause the formation of novel discotic mesophases characterized by a superstructure.