Columnar mesophases of cyclic trimers of disubstituted acetylenes

Abstract

Hexa(4-alkyphenoxymethyl)benzenes, 4(with n= 4, 7, 9) were prepared by the alkylation of hexa(bromomethyl)-benzene and/or Cp₂Co catalysed cyclotrimerization of the corresponding 1,4-di(4-alkylphenoxy)but-2-yne monomer, 2. The derivative 4(n= 4) is crystalline. The derivative 4(n= 7) displays an enantiotropic columnar mesophase and compound 4(n= 9) displays a monotropic columnar mesophase whose polarized optical microscopic textures are typical of D_ho mesophases. An additional columnar mesophase of the derivative 4(n= 7) is monotropic. Hexa(4-alkoxyphenyl)benzenes, 3(n= 4–9) were prepared by PdCl₂(PhCN)₂ catalysed cyclotrimerizations of the corresponding 1,2-di(4-alkoxyphenyl)acetylenes, 1. The derivatives 3(n= 6–9) form anisotropic glasses whose columnar mesophases become more fluid as the temperature approaches isotropization. Methyl branches in either the mesogen or the alkoxy substituents promotes solidification, whether it is to a crystalline phase or to an anisotropic glass.