Molecular design of amphotropic materials: double-headed diol-based mesogens incorporating rigid structural units

Abstract

The syntheses of novel bolaamphiphilic triol and tetraol compounds incorporating rigid structural units are described. Their liquid-crystalline properties were investigated by polarizing microscopy, differential scanning calorimetry and in some cases also by means of X-ray diffraction. Most 4,4-disubstituted biphenyl derivatives exhibit one or more smectic phases (predominantly S_A but also S_c, S_B, S_G and S_k) and extraordinarily high clearing temperatures. No thermotropic liquid-crystalline properties could be detected for bolaamphiphiles incorporating a single 1,4-disubstituted phenyl ring or a 2,6-disubstituted naphthalene ring system, but for naphthalene derivatives a lyotropic smectic A phase was induced by addition of water. If one of the diol groups of the biphenyl-derived bolaamphiphiles is replaced by a single hydroxy group or by a carboxylic acid group the mesophase stability is decreased. Mesomorphic properties are lost if the hydrogen-bonding density is further diminished by the replacement of one diol group by an ethyl carboxylate group. However, in these cases lyotropic liquid-crystalline phases can be induced by the addition of water.