Effect of the Introduction of a Chlorine Atom into the Aromatic Fragment of the 1,3-Diketone Ligand on the Luminescence Efficiency of Novel Eu 3+ Ion Coordination Compounds

study was carried out on the effect of a heavy chlorine atom introduced into the aromatic fragment of a 1,3-diketone ligand in Eu 3+ coordination compounds on the spectral and luminescent properties of complex compounds. The data obtained from the absorption, optical excitation, fluorescence, and phosphorescence spectra as well as from the kinetics of the luminescence intensity permit estimation of the efficiency of energy transfer processes within the compounds studied. Introduction of a heavy chlorine atom was found to raise the energy of the first excited singlet state from 24,500 to 26,000 cm –1 but not affect the energy of the triplet level of the ligand. Furthermore, introduction of a chlorine atom leads to a decrease in the nonradiative relaxation constant (from 1290 to 840 s –1 ) and thereby triples the luminescence quantum yield from 23 to 64%. Hence, a new approach for the rational construction of useful coordination compounds of Eu 3+ ions with 1,3-diketone ligands has been developed consisting of the substitution of a hydrogen atom by a heavy chlorine atom in the aromatic fragment of the ligand.