Photoluminescent lanthanide(iii) coordination polymers based on 2-{[(4-methylphenyl)amino]methylene}-5,5-dimethylcyclohexane-1,3-dione

Abstract

Five novel lanthanide(III) coordination polymers, namely, europium(III), samarium(III), terbium(III), dysprosium(III) and gadolinium(III), with an enaminone derivative – 2-{[(4-methylphenyl)amino]methylene}-5,5-dimethylcyclohexane-1,3-dione (L), were obtained by two different synthesis methods. The composition and structure were investigated using IR spectroscopy, elemental analysis as well as powder and single-crystal X-ray diffraction (XRD) analysis. According to single-crystal XRD analysis data, the ligand exhibits bidentate bridging coordination mode, forming a polymer layered structure with the common formula [LnL₂(NO₃)₃]_n. All obtained compounds were isomorphous to each other. Upon investigating the photoluminescent properties, the quantum yield of the ligand was found to be 74%, but complex formation significantly decreased the quantum yield, such as for the europium complex, the quantum yield was only 7.6%. In the case of ligand, the kinetic curve was described by a biexponential function with luminescence lifetimes of 3.2 ns and 1.1 ns. For complexes, luminescence lifetime appeared in the millisecond region; it equalled 1.20 ms for the europium(III) complex and 0.52 ms for the terbium(III) complex. Triplet state energy was determined by both DFT calculations as well as registration of phosphorescence for the gadolinium(III) complex. The highest color purity was found to be achieved at 95.58% in the case of the europium(III) complex.