UNSYMMETRICAL ALKOXY-SUBSTITUTED TRIPHENYLENES - THE DEPENDENCE OF MESOMORPHISM ON MOLECULAR SHAPE

Several series of unsymmetrical hexa-alkoxytriphenylenes have been pre pared. For almost every series a maximum in the Col(h)-I clearing poin t is found for the most symmetrical triphenylene, i.e. when all six al koxy chains are of equal length. A similar trend is found for the melt ing points (T-m), although the effect is not so pronounced. A minimum length is required for formation of a columnar mesophase (Col(hd)) Aft er this critical value has been reached for short alkoxy chains, much lower Col(h)-I temperatures are then observed for longer chains. Order ed hexagonal columnar phases required for efficient photoluminescence and electroluminescence have been found for several asymmetrical homol ogues with comparable TCol-I to those observed for the symmetrical hom ologues, but also with lower T-m. This may facilitate the preparation of mixtures of triphenylenes with the desired ordered hexagonal column ar phases with a TCol-I and a T-m below room temperature.