CALIX[4]ARENE PODANDS AND BARRELANDS INCORPORATING 2,2'-BIPYRIDINE MOIETIES AND THEIR LANTHANIDE COMPLEXES - LUMINESCENCE PROPERTIES

A new family of cone-shaped podands and barrel-shaped cryptands based on calix[4]arenes incorporating 5,5'-substituted 2,2'-bipyridine subun its were prepared and characterized. The Eu3+ and Tb3+ complexes of th e podands bearing two, three, or four bipyridine chromophores could be isolated. High molar absorption coefficients (epsilon(max) = 39 600 M -1 cm(-1) for Eu4 and 26 700 M-1 cm(-1) for Eu 3) and high metal lumin escence quantum yields (16% for Eu4 and 15% for Eu3) were obtained. Mo lecular dynamics simulations on Eu4 showed that the bipyridine arms wr ap around the lanthanide cation, efficiently shielding the cation from solvent molecules. In the presence of chloride counterions the fourth bipyridine arms does not coordinate the lanthanide ion. Ligands beari ng two bipyridine units and two additional functional groups - ethyl b utyrate or N-propylpyrrole - did not give stable lanthanide complexes, The barreland containing two calix[4]arene moieties and four bipyridi ne groups did not form complexes with lanthanide ions, most probably b ecause of the rigidity of the ligand.