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 fluoresce nce emission. The structure of this photoresponsive supramolecular sys tem is based on two diazacrown ether moieties (N2O4) linked through tw o anthracene chromophore-containing flexible spacers. 1 displays a dua l (locally excited and excimer-type) fluorescence emission, and the re lative contribution (Phi(FE)/Phi(FM)) of these emissions is sensitive to metal cations. A spectroscopic study shows that the optical respons es are dependent on the nature of the complexed cation, and the more p ronounced effect is noticed with Rb+. X-ray crystallographic, photophy sical, and binding studies confirm that two Rb+ cations are held withi n the hydrophilic N2O4 parts with participation of the four phenolic o xygen atoms to complexation, leading to the maximum overlap between th e anthracene nuclei in both the ground and excited states. The mononuc lear 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 nonc ooperative behavior is observed. This new supramolecular system can th us be used for sensitive metal cation detection and recognition, espec ially for Rb+.