Shedding Light on Eu(III) β‐Diketonate Compounds with 1,2‐Bis(diphenylphosphino)ethane Oxide Ligand: an Optical Study.

A series of novel lanthanide β‐diketonate coordination compounds containing the ancillary ligand bis(diphenylphosphino) oxide (dppeO2) have been synthesized, characterized, and studied spectroscopically. The compounds of formulas Ln(β‐dik)3(dppeO2), where Ln: Eu and Gd and β‐dik ligands as tta (Ln‐1), btf (Ln‐2), bzac (Ln‐5) and tfac (Ln‐4), and Ln2(β‐dik)6(dppeO2) with ligand dbm (Ln‐3) and fod (Ln‐6). Their photophysical properties were investigated from the Judd‐Ofelt intensity parameters (Ωλ ${{\Omega }_{\lambda }}$), radiative (Arad ${{A}_{rad}}$) and non‐radiative (Anrad ${{A}_{nrad}}$) rates, intrinsic (QEuEu ${{Q}_{Eu}^{Eu}}$) and overall (QEuL ${{Q}_{Eu}^{L}}$) quantum yields, and CIE (x,y) color coordinates. The Eu‐5 and Eu‐6 compounds have the first excited triplet states T1 (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 T1 energies. The Arad ${{A}_{rad}}$ values were predominantly driven by the intensity parameter Ω2 ${{\Omega }_{2}}$ , suggesting more pronounced angular changes in the first coordination sphere of the Eu3+ ion. The Anrad ${{A}_{nrad}}$ values also exhibited significant changes with the β‐diketonate ligands. Eu‐1 showed the highest value of QEuL ${{Q}_{Eu}^{L}}$ (60 %), indicating a more efficient intramolecular energy transfer process. On the other hand, Eu‐5 and Eu‐6 compounds showed QEuL ${{Q}_{Eu}^{L}}$ values equal to 18.7 % and 16.5 %, respectively, which indicates the presence of luminescence quencher channels. [ABSTRACT FROM AUTHOR]