Effect of the Chlorine Atom Adding to 1,3-Diketone Ligand Aromatic Fragment on the Luminescence Efficiency of Novel Eu3+ Ion Coordination Compounds

Abstract

We studied the effect of a heavy chlorine atom added to the aromatic fragment of a 1,3-diketone ligand in Eu³⁺ ion 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 kinetic dependences of the luminescence intensity, allows us to estimate the efficiency of energy transfer processes within the studied compounds. It was found that adding a heavy chlorine atom leads to an increase in the energy of the first excited singlet state from 24500 to 26000 cm^–1 and does not affect the energy of the triplet level of the ligand. Also, adding chlorine leads to a decrease in the nonradiative relaxation constant (from 1290 to 840 s^–1), and consequently increases the luminescence quantum yield up to three times from 23 to 64%. Thereby, a new approach in the rational construction of coordination compounds of Eu3⁺ ions with 1,3-diketones class ligands has been developed, consisting in substitution of hydrogen with heavy chlorine atom in the aromatic fragment of ligand.