Shedding light on Eu(III) β-diketonate compounds with 1,2-Bis(diphenylphosphino)ethane oxide ligand

Abstract

A series of novel lanthanide beta-diketonate coordination compounds containing the ancillary ligand bis(diphenylphosphino) oxide (dppeO(2)) have been synthesized, characterized, and studied spectroscopically. The compounds of formulas Ln(beta-dik)(3)(dppeO(2)), where Ln: Eu and Gd and beta-dik ligands as tta (Ln-1), btf (Ln-2), bzac (Ln-5) and tfac (Ln-4), and Ln(2)(beta-dik)(6)(dppeO(2)) with ligand dbm (Ln-3) and fod (Ln-6). Their photophysical properties were investigated from the Judd-Ofelt intensity parameters (Omega(lambda)), radiative (A(rad)) and non-radiative (A(nrad)) rates, intrinsic (Q(Eu)(Eu)) and overall (Q(Eu)(L)) quantum yields, and CIE (x,y) color coordinates. The Eu-5 and Eu-6 compounds have the first excited triplet states T-1 (around 18802 and 18976 cm(-1), respectively) almost resonant with the Eu3+ 5D0 emission level, whereas the complexes Eu-1, Eu-2, Eu-3, and Eu-4 exhibited higher T-1 energies. The A(rad) values were predominantly driven by the intensity parameter , suggesting more pronounced angular changes in the first coordination sphere of the Eu3+ ion. The A(nrad) values also exhibited significant changes with the beta-diketonate ligands. Eu-1 showed the highest value of Q(Eu)(L)(60 %), indicating a more efficient intramolecular energy transfer process. On the other hand, Eu-5 and Eu-6 compounds showed Q(Eu)(L )values equal to 18.7 % and 16.5 %, respectively, which indicates the presence of luminescence quencher channels.