Synthesis, structure and tuneable white-light emission of dinuclear Eu(III), Tb(III)- mixed Schiff base complexes

A new family of lanthanide-Schiff base complexes have been synthesized and fully characterized from the novel Schiff base ligand: H2L1 (acetic acid 2-hydroxy-benzylidene-hydrazide). The single crystal X-ray structure and mass spectroscopy reveal the isostructural dinuclear complexes: [Ln(2)L(1)(HL1) (3)(NO3)] where Ln = Sm, Eu, Gd and Tb. Upon excitation of the Ln(III) complexes in solution, their luminescence spectra display the broad ligand centred (LC) band at similar to 470 nm as well as the narrow f-f transitions. In EuIII complex, the LC emission is efficiently quenched, because of the better triplet state energy match to the Eu-III-D-5(4) excited states. Doping methods of Eu-III with Tb-III into the complexes: [EuxTb1-x(L-1)(HL1)(3)(NO3)], x = 0.5 (A), 1.0 (B) and 1.5 (C); in MeOH/DCM (1:10), have revealed variable colours. By careful control of the amounts of EuIII and TbIII in the dinuclear mixed EuTb-complexes, white-light emission is obtained from blue LC band, green TbIII luminescence and red EuIII luminescence. Such behaviour is attributed to the efficient sensitization of EuIII by the ligand and the metal to metal energy transfer from TbIII to EuIII excited 4f states.