Spectroscopic study of Tb3+(β-diketonate)3:: α-cyclodextrin inclusion compounds in aqueous solution

In this work we describe how the inclusion of Tb3+ beta-diketonate chelates into the hydrophobic cavity of alpha-cyclodextrin enhances the solubility of the complexes in aqueous medium and leads to changes in their photophysical properties. To this end, the complexes [Tb(ppa)(3)(H2O)(2)] and [Tb(ppa)(3)(phen)](ppa=3-phenyl-2,4-pentanedione; phen = phenantroline) were synthesized and characterized, and they were then included into alpha-cyclodextrin pockets. This inclusion was confirmed by H-1 NMR spectroscopy and the stoichiometry was determined by means of the Job method. In the excitation spectra, the maximum intensity wavelength of the inclusion compounds [Tb(ppa)(3)(H2O)(2)]: alpha-CD and [Tb(ppa)(3)(phen)]: alpha-CD were displaced 15 and 60 nm respectively when compared with the non-CD starting complexes. The typical Tb3+ emission bands were maintained after inclusion of the complexes into alpha-CD and their subsequent solubilization in aqueous medium.