The effect of luminescent enhancement under exchange of the auxiliary ligand in Europium(III) tris(1,3-diphenyl-1,3-propanedionato) monohydrate was investigated by steady-state and time-resolved transient absorption spectroscopy. The excited state relaxation dynamics of this complex was analysed through a comparison of the experimental data obtained for several model compounds, namely Eu(DBM)3·NH3, Eu(DBM)3.EDA, Eu(DBM)3.Phen, Al(DBM)3 and dibenzoylmethane (DBM) in various solutions and polymer matrices. The results show there is no linear relationship between enhancement of the emission quantum yield and the luminescent lifetime, which suggests that the auxiliary ligand reduces the rate of nonradiative relaxation of the lanthanide ion, but also affects the excited state energy transfer from ligand to metal ion. Transient absorption data shows a clear correlation between the efficiency of the energy transfer and the degree of triplet state population expressed by an amplification of the signal for its excited state absorption band on going from Eu(DBM)3·H2O to the Eu(DBM) = .L complex. The results show that this auxiliary ligand exchange acts as a "switch" turning the intersystem crossing on or off as a competitive pathway for excited state relaxation of the europium(III) complexes.
Keywords: Chemosensors; DBM; Europium(III) β-diketonates; Transient absorption.
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