SUPRAMOLECULAR STRUCTURES AND CHEMICAL SENSING

In the development of new materials for molecular recognition the use of supramolecular structures proves to be a successful approach. By im plementation of structural characteristics, such as the long range ord er in liquid crystalline materials, highly stabilized ionic centres or molecular holes, different sensitivities can be achieved for solvent vapours. Differentiation may be based on donicity, acceptor properties , size and shape of the analyte. The molecular order found in liquid c rystals will be disturbed by incorporation of guest molecules accordin g to their size and shape. Changes in the degree of order can be surve yed with optical labels as well as by dielectric measurements with an interdigital capacitor coated with the mesophase. Carbenium ions such as triphenyl methane dyes, characterized by an electron deficiency, gi ve a massive change in optical absorbance when exposed to analytes wit h pronounced electron donor properties. A further opportunity is prese nted by the host-guest chemistry of, e.g., calix[4]resorcinearenes. Th e inclusion of solvent molecules in these molecular cavities can be op timized by molecular modelling, thus giving way to highly specific hos t-guest interactions. In combination with mass sensitive devices such as the quartz microbalance or the surface acoustic wave oscillator the se hollows yield highly sensitive systems.