Investigation of the driving forces of molecular selforganization is one of the most exciting and most rapidly growing areas of chemical research. In this respect, ordered structures with liquid-crystalline (LC) properties are of special interest, because they are reversibly formed under thermodynamic equilibrium conditions and combine order and mobility on molecular, supramolecular, and macroscopic levels. The mobility enables them to respond to different external stimuli by changing their configuration, which in turn determines their importance in biological systems and technical applications. In conventional LC materials rod-or disklike anisometric rigid units, which provide long-range orientational order, are connected to flexible alkyl chains, which are largely responsible for positional order and mobility. This design principle leads to the well-known nematic, smectic, and columnar LC phases. A characteristic feature of such LC materials is a molecular topology in which rigid cores and flexible chains are connected in such a manner that the parallel organization of the rigid segments and the segregation of the incompatible molecular parts enhance each other.
Exciting new mesophase morphologies can be realized if rodlike (calamitic) rigid units are combined with two incompatible subunits in a competitive and nonlinear manner. Examples are bolaamphiphilic biphenyl derivatives carrying a long lateral alkyl chain. In such bolaamphiphiles, the strongest attractive forces (hydrogen bonding) act at the two termini of a rigid calamitic core. The lateral alkyl chains represent a third group of units that are incompatible with both the polar terminal diol groups and the rigid biphenyl cores. As a consequence, each of these units segregates into its own subspace, and a series of unusual columnar mesophases results. They are built up by networks of cylinders, formed by ribbons of the biphenyl cores which are held together by ribbons of hydrogen-bonding networks (see Figure ). The