SYNTHESIS, STRUCTURAL, SPECTROSCOPIC, AND ALKALI-METAL CATIONS COMPLEXATION STUDIES OF A BIS-ANTHRACENEDIYL MACROTRICYCLIC DITOPIC RECEPTOR

The macrotricyclic bis-anthracenediyl receptor 1 has been prepared in order to study the interplay between cation complexation and fluorescence emission. The structure of this photoresponsive supramolecular system is based on two diazacrown ether moieties (N2O4) linked through two anthracene chromophore-containing flexible spacers. 1 displays a dual (locally excited and excimer-type) fluorescence emission, and the relative contribution (Phi(FE)/Phi(FM)) of these emissions is sensitive to metal cations. A spectroscopic study shows that the optical responses are dependent on the nature of the complexed cation, and the more pronounced effect is noticed with Rb+. X-ray crystallographic, photophysical, and binding studies confirm that two Rb+ cations are held within the hydrophilic N2O4 parts with participation of the four phenolic oxygen atoms to complexation, leading to the maximum overlap between the anthracene nuclei in both the ground and excited states. The mononuclear and binuclear rubidium complexes exhibit high stability constants in solution (K-1 = 6.0 x 105 M(-1); K-2 = 6.3 x 104 M(-1)) and a noncooperative behavior is observed. This new supramolecular system can thus be used for sensitive metal cation detection and recognition, especially for Rb+.