Design principles are discussed for the polyfunc-Design principles are discussed for the polyfunctional crown compounds that are able to act as optical tional crown compounds that are able to act as optical molecular sensors or photocontrolled receptors with respect molecular sensors or photocontrolled receptors with respect to metal and ammonium cations. The bibliography includes to metal and ammonium cations. The bibliography includes 237 references 237 references. .

A series of new viologen analogues bearing two ammonioalkyl groups (2-4) were synthesized in order to study their complexation with bis(18-crown-6)stilbene (1b). Electronic spectroscopy and 1 H NMR measurements show that in acetonitrile, bis(crown) stilbene 1b forms highly stable 1 : 1 and 2 : 1 chargetransfer (CT) complexes with p-acceptors 2-4 owing to host-guest bonding. The influence of geometric and electronic factors on the complex formation constants are discussed. The structures of the supramolecular CT complexes are analyzed on the basis of 1 H and 13 C NMR data obtained in solution and in the solid state. X-Ray diffraction data for 1b and for model tetramethoxystilbene are also reported.

The formation of complexes between a bisstyryl dye containing two benzo-15-crown-5 ether groups, 2, and Mg2+, Ca2+, Sr2+, and Ba2+ ions was studied in acetonitrile solution by using a spectrophotometric approach. In contrast to its monostyryl analogue 1, which shows a rather low cation-binding selectivity, the bisstyryl dye 2 selectively binds the Sr2+ and Ba2+ ions because of formation of intramolecular sandwich complexes. Alkaline-earth metal cations induce substantial blue shifts of the absorption maximum of 1 and 2, particularly in the case of sandwich complex formation. The emission behavior of 1 and 2 and their Ba2+ complexes in acetonitrile solution has also been studied. In both cases, complex formation leads to a blue shift of the fluorescence maximum and a decrease in the emission quantum yield. The fluorescence decay is monoexponential for the complex of 1 and biexponential for that of 2. The longer-lived fluorescence component, which corresponds to the lower-energy band in the steady-state spectrum, is assigned to an intramolecular excimer state.

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