Study of the fluorescence of some newly synthesized europium complexes with pyrazolone derivatives

Some europium complexes with pyrazolone derivatives and 1,10-phenanthroline were synthesized and characterized. The europium ion was found to coordinate to O atoms of the pyrazolone derivatives and to N atoms of 1,10-phenanthroline. A strongly ligand-localized UV absorption leads to the europium-centered emissions between 580 and 750 nm which were assigned as the 5D0&rarr7F0,1,2,3,4 and 5D1&rarr7F3,4 transitions. A low site symmetry for the Eu3+ ion was confirmed from the observation of 5D0&rarr7F0 emission and from the splitting of the other bands. In contrast to many Eu complexes that have been investigated a rather weak emission was measured by introduction of a Schiff base to form a ternary complex with the pyrazolone derivative. The long fluorescence lifetimes of these complexes suggest an energy transfer process from ligands to Eu3+ ion through the triplet state of the ligands.