Modification of the luminescence properties of an Europium(III) tris(β-diketonate) complex by inclusion in γ-cyclodextrin and 2,3,6-trimethyl-γ-cyclodextrin

A 1:1 inclusion compound between octakis(2,3,6-tri-O-methyl)-gamma-cyclodextrin (TRIMEG) and the chelate complex Eu(NTA)(3)center dot 2H(2)O (NTA = 1-(2-naphthoyl)-3,3,3-trifluoroacetonate) was prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and photoluminescence spectroscopy. The results were compared with those obtained for the corresponding native gamma-CD adduct. Excitation and emission spectra were measured, and the lifetimes were determined for the Eu3+ first excited state (D-5(0)). The results indicate the presence of only one low-symmetry environment for the Eu3+ cations in the inclusion compounds. Encapsulation of the Europium. complex in the two CDs increases the quantum efficiency of the ligand-to-metal energy transfer pathway, but the efficiency of the Eu3+ sensitization was significantly higher with TRIMEG as the host molecule. This may be related with the observation that the two hosts appear to have different influences on the Eu3+ coordination environments for the guest molecule.