2D polymeric lanthanide(III) compounds based on novel bright green emitting enaminone ligand

Abstract

New enaminone derivative, 2-{[(4-methoxyphenyl)amino]methylene}-5,5-dimethyl-cyclohexane-1,3-dione (HL), and lanthanide(III) compounds based on it [Ln(HL)2(NO3)3]n, (where Ln3+=Eu (1Eu), Sm (2Sm), Tb (3 Tb) and Dy (4Dy)) have been synthesized. The complexes have been fully characterized by spectroscopic and analytical methods including single crystal X-ray structure. To establish closer intermolecular contacts and HOMO/LUMO energy, the Hirshfeld surface analysis, as well as DFT calculations has been carried out. According to single-crystal X-ray diffraction analysis ligand exhibits bidentate-bridging mode. This leads to the formation of polymeric structure as layer, arranged parallel to ab crystallographic plane. The lanthanide polyhedron is close to bicapped square antiprism. All obtained compounds are isomorphous to each other. The study of photoluminescence showed the presence of a bright green emission of the ligand with a quantum yield of 41 %. The weak sensitization occurs only in case of europium(III) complex leading to apparent luminescence quantum yield of 0.021 %, with ∼4 % sensitization efficiency. Emission spectra of other compounds are the same to the ligand one.