Unsymmetrical alkoxy-substituted triphenylenes: the dependence of mesomorphism on molecular shape

Several series of unsymmetrical hexa-alkoxytriphenylenes have been prepared. For almost every series a maximum in the Col(h)-I clearing point is found for the most symmetrical triphenylene, i.e. when all six alkoxy chains are of equal length. A similar trend is found for the melting points (T-m), although the effect is not so pronounced. A minimum length is required for formation of a columnar mesophase (Col(hd)) After this critical value has been reached for short alkoxy chains, much lower Col(h)-I temperatures are then observed for longer chains. Ordered hexagonal columnar phases required for efficient photoluminescence and electroluminescence have been found for several asymmetrical homologues with comparable TCol-I to those observed for the symmetrical homologues, but also with lower T-m. This may facilitate the preparation of mixtures of triphenylenes with the desired ordered hexagonal columnar phases with a TCol-I and a T-m below room temperature.