Lateral extension induces columnar mesomorphism in crucifix shaped quinoxalinophenanthrophenazines

Abstract

Reported here is the columnar mesomorphism of board shaped dyes based on quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine (TQPP) derivatives that was induced by an increase in lateral bulk. TQPP derivatives with protons, tert-butyl and 4-tert-butyl-phenyl groups in positions 2 and 11 are compared, as well as dodecylthio, dodecyloxy, phytanylthio, and phytanyloxy side-chains. Only derivatives with 4-tert-butyl-phenyl groups display columnar liquid crystal phases over wide ranges of temperature while all other TQPPs are not liquid crystalline except for the compound with tert-butyl groups and phytanyloxy side-chains that shows a Colr mesophase over a temperature range of 26 °C. The sole attachment of phytanyl groups does not effectively induce columnar mesophases. However, the lateral attachment of bulky groups to the TQPP core induces columnar mesomorphism because of the in-plane aspect ratio decrease and the favored twisted or helical π-stacking of the molecules in columns rather than the parallel co-planar packing.