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.

Dinuclear and polymeric lanthanide complexes of the types [Ln2(fod)6(μ-bpm)] (Ln = Nd–Lu) and [Ln(fod)3(bpm)]n (Ln = La and Pr) have been isolated and investigated by 1H NMR and steady-state emission spectroscopies. The 1H NMR spectra of all the complexes and their parent chelates have been analysed in detail. The steady-state emission properties of the Pr, Sm, Eu, Tb, Dy and Tm complexes in chloroform are discussed by taking into consideration the triplet levels of the coordinated ligands and their energy match with the emitting levels of Ln(III) ions. The work emphasizes that the combination of fod and bpm is most effective for the sensitization of red and pink emissions of Eu(III) and Sm(III) ions, respectively. Despite bpm being an efficient sensitizer for the luminescence of Tb(III) and Dy(III) ions, a combination of bpm and fod is not much effective for the sensitization of these ions. Among many reasons including the energetic one, the depopulation of bpm centered excited states to the excited states of fod in terbium and dysprosium complexes could be one of the reasons.Figure optionsDownload as PowerPoint slideHighlights
► An extended series of dinuclear lanthanide complexes has been isolated and thoroughly characterized.
► The 1H NMR chemical shifts of the paramagnetic complexes have been analysed and discussed.
► The visible light emission of the complexes has been investigated in solution by taking into consideration the triplet state of the antenna ligands.
► The combination of fod and bpm is very effective for the sensitization of red and pink emissions from Eu(III) and Sm(III) ions, respectively.
► These visible light emitting complexes are excellent materials for possible fabrication of light emitting devices.