Spectroscopic study of the inclusion compound of b-cyclodextrin and Tris(dibenzoylmethane)europium(III) dehydrate.

Abstract

Photoluminescent properties of the inclusion compound of b-cyclodextrin and tris(dibenzoylmethane)europium(III) dihydrate, in the solid state, are reported. This compound and the precursor salt, Eu(DBM)3 • 2H2O (DBM_dibenzoylmethane), were characterized by IR spectroscopy, X-ray powder diffraction and differential scanning calorimetry. The emission data indicate that the host-guest interaction (at 77 K) causes an intensification of some bands corresponding to the 5D0.7FJ (J_0–4) transitions associated with one of the site symmetries existing in the guest compound. Based on the luminescence spectrum of the supramolecular compound the Vl experimental intensity parameters (l_2 and 4) were calculated for the electronic transitions 5D0.7F2, 4. The value of the V2 intensity parameter for this new compound is smaller than for the guest, suggesting an effective interaction between the b-cyclodextrin and the closer chemical environment of the Eu3_ ion. On the other hand, the values of the V4 parameter for the inclusion compound are twice larger than the one of the guest, suggesting that the steric effect is more significant in the supramolecular species. Comparison between the luminescence lifetimes of the guest and inclusion compound indicates that the b-cyclodextrin contributes to increase the lifetime of the 5D0 emitting level. The time-resolved spectra of the inclusion compound corroborate the presence of more than one site symmetry occupied by the rare earth ion.