Novel hexasubstituted triphenylene discotic liquid crystals having three different types of peripheral substituent

Abstract

The synthesis and mesomorphic properties of a variety of novel hexasubstituted triphenylene derivatives having three different types of peripheral substitutions are described. Monobromination of 2,3, 6, 7-tetrakis ( pentyloxy) triphenylene 4, prepared by Suzuki coupling of 2-iodo-3', 4,4',5-tetrakis (pentyloxy) biphenyl 2 and phenylboronic acid followed by cyclization, yields 10-bromo-2, 3, 6,7-tetrakis( pentyloxy) triphenylene 5. Nucleophilic aromatic displacement of the bromine with the potassium salt of pentanethiol, followed by bromination, yields 2-bromo-6,7,10,11-tetrakis(pentyloxy)-3-(pentylsulphanyl) triphenylene 7 having a bromo, thioalkyl and alkoxy-substituted periphery of the triphenylene nucleus. The reaction of 7 with copper( I) cyanide gives the cyanotriphenylene derivative 8, while palladium-copper catalysed alkynylation of 7 results in the synthesis of the substituted alkyne derivative 9. The deprotected alkyne 10 was converted to dimer 11 where two molecules of a monothioalkyl-tetra-alkoxytriphenylene are connected via a rigid pi-conjugated diacetylene bridge. Compounds 7, 8, 9, 10 form hexagonal columnar phases while the dimer 11 shows a discotic nematic phase.