Effect of symmetric substitution on the phenyl groups of Eu3+–dibenzoyl methane complexes on their luminescence properties

Complexes of Eu3+ ion and ligands like dibenzoylmethane (DBM) as well as flouro- and methoxy-substituted DBMs have been prepared and characterized. Peak maxima and line shapes of the π–π* transitions arising from the ligands in these complexes were very sensitive to the nature of the substituents attached to the phenyl groups of DBM. Symmetric substitution at both the phenyl groups led to improved luminescence in terms of higher quantum yields of emission and longer lifetime of the excited state (5D0) of Eu3+ ions. Effective averaging/cancellation of the dipole–dipole interactions in symmetrically substituted ligands and the associated decrease in the extent of quenching were responsible for the improved luminescence from such complexes.