A comparative study of 1H NMR and sensitized visible light emission of an extended series of dinuclear lanthanide complexes

An extended series of dinuclear lanthanide β-diketonate complexes of the type [Ln2(fod)6(μ-bpm)] (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; fod is the anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione; bpm = 2,2′-bipyrimidine) and polymeric complexes of the type [Ln(fod)3(bpm)]n (Ln = La and Pr) have been isolated and thoroughly investigated in solution, by means of 1H NMR and steady-state luminescence spectroscopies. The 1H NMR chemical shift for the protons of paramagnetic complexes is analysed and discussed. The typical sensitized red, pink, green and yellow emission of Pr(III)/Eu(III), Sm(III), Tb(III) and Dy(III) complexes, respectively, is observed upon the excitation of the coordinated ligands. The comparison of the steady-state luminescence intensities of the complexes reveals that ligand-to-metal energy transfer is most efficient in Eu(III) complex followed by Sm(III) and Pr(III) complexes. The Tb(III) and Dy(III) complexes show relatively weak luminescence due to inefficient energy transfer.