A study on the NIR-luminescence emitted from ternary lanthanide [Er(III), Nd(III) and Yb(III)] complexes containing fluorinated-ligand and 4,5-diazafluoren-9-one

A series of lanthanide complexes Ln(tfnb)3dafone, Ln(hfth)3dafone and Ln(pfnd)3dafone (Ln = Er, Nd and Yb) with fluorinated-ligand 1-(2-naphthyl)-4,4,4-trifluoro-1,3-butanedionate (Htfnb), 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)hexane-1,3-dione (Hhfth) and 4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-pentadecafluoro-1-(naphthalen-2-yl)decane-1,3-dione (Hpfnd) served as main sensitizers, respectively, and 4,5-diazafluoren-9-one (dafone) as the synergistic ligand were synthesized. Upon excitation at the maximum absorption of the ligands, the complexes all show the characteristic near-infrared (NIR) luminescence of the corresponding Ln3+ ions, which is due to efficient energy transfer from the ligands to the central Ln3+ ions via an antenna effect. Moreover, an indirect excitation model is proposed and the influence of ligands on the luminescence properties of the complexes is further discussed.