Spectroscopic study of the inclusion compound of beta-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 diff raction and differential scanning calorimetry. The emission data indicate t hat 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 associat ed 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 t he electronic transitions D-5(0) -->F-7(2,4). The value of the Omega(2) int ensity parameter for this new compound is smaller than for the guest, sugge sting 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 on e of the guest, suggesting that the steric effect is more significant in th e supramolecular species. Comparison between the luminescence lifetimes of the guest and inclusion compound indicates that the beta-cyclodextrin contr ibutes to increase the lifetime of the D-5(0) emitting level. The time-reso lved spectra of the inclusion compound corroborate the presence of more tha n one site symmetry occupied by the rare earth ion. (C) 1999 Elsevier Scien ce B.V. All rights reserved.