Spectroscopic study of the inclusion compound of β-cyclodextrin and Tris(dibenzoylmethane)europium(III) dihydrate

Photoluminescent properties of the inclusion compound of beta-cyclodextrin and tris(dibenzoylmethane)europium(III) dihydrate, in the solid state, are reported. This compound and the precursor salt, Eu(DBM)(3) . 2H(2)O (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 D-5(0) --> F-7(J) (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 Omega(lambda) experimental intensity parameters (lambda = 2 and 4) were calculated for the electronic transitions D-5(0) -->F-7(2,4). The value of the Omega(2) intensity parameter for this new compound is smaller than for the guest, suggesting an effective interaction between the beta-cyclodextrin and the closer chemical environment of the Eu3+ ion. On the other hand, the values of the Omega(4) 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 beta-cyclodextrin contributes to increase the lifetime of the D-5(0) 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. (C) 1999 Elsevier Science B.V. All rights reserved.