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

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 π-conjugated diacetylene bridge. Compounds 7, 8, 9, 10 form hexagonal columnar phases while the dimer 11 shows a discotic nematic phase.