Lateral extension induces columnar mesomorphism in crucifix shaped quinoxalinophenanthrophenazines This paper is dedicated to Professor Makhlouf J. Haddadin on the occasion of his 80th birthday and 50 years of outstanding service to the American University of Beirut

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. ©2014 Elsevier Ltd. All rights reserved.