A COOPERATIVE EFFECT IN SODIUM-CATION COMPLEXATION BY A MACROCYCLIC BIS(9,10)ANTHRACENO-CROWN ETHER IN THE GROUND-STATE AND IN THE EXCITED-STATE

The bisanthraceno-crown ether displays a dual fluorescence consisting of a 'monomer' and excimer emission. Its structural flexibility is dem onstrated by the temperature dependence of the total fluorescence emis sion. The compound forms a 1:1 complex with K+ in methanol (beta appro ximate to 10 M(-1) at +25 degrees C), whereas a 1:2 complex is observe d with Na+ in both methanol and acetonitrile with a positive cooperati ve effect. At +25 degrees C in acetonitrile the overall binding consta nt beta deduced from UV measurements (beta approximate to 3.7 x 10(4) M(-2)) is lower than that obtained from fluorescence data (beta approx imate to 10(5) M(-2)), indicating an enhancement of the complexation a bility in the excited singlet state.