Quantum Yield and Photoluminescence Intensity Enhancement Effects of a Diphosphine Dioxide Ligand on a 6-Coordinate Eu(III)-β-Diketonate Complex with Low Luminescence

Abstract

Tris­{6,6,7,7,8,8,8-heptafluoro-1-[2-(9,9-dimethylfluorenyl)]-1,3-octanedionate} europium­(III) (Eu­(III)­(hfod)3 1) was synthesized, which was designed to have low luminescence and a large absorption coefficient in order to elucidate the coordination effects of phosphine oxide ligands. The quantum yield (ΦTOT) and photoluminescence intensity of complex 1 were dramatically enhanced by coordinating a diphenyl-4-(dibutylphosphinyl)­butyl phosphine oxide (DPDB) ligand, thanks to the increased intrinsic photoluminescence quantum yield of the lanthanide (ΦLn) and the increased energy transfer efficiency (ΦET) in the solution and solid states. In the solid state, there was no energy dissipation by solvent molecules. This excluded the steric shielding effects of the DPDB ligand and allowed the effects of the ligand field environment to be extracted. ΦLn and ΦET of complex 2 were much larger in the solid state than those in the solution state, resulting in larger ΦTOT (solution state: ΦLn 0.50, ΦET 0.42, and ΦTOT 0.21 and solid state: ΦLn 0.74, ΦET 0.47, and ΦTOT 0.35). Larger asymmetry ratios (ratio R) of Eu­(III)­(hfod)3(DPDB) 2 than those of complex 1 in the solution and solid states indicate that the ligand field of the Eu­(III) ion becomes more asymmetric by coordination of the DPDB ligand. Density functional theory calculations showed that ΦLn and ΦET increased when the ligand field around the Eu­(III) ion became more asymmetric. Based on these results, we propose a hypothesis on the enhancement of the photoluminescence intensity of 6-coordinated Eu­(III)-β-diketonate by a DPDB ligand. When a DPDB ligand coordinates to a Eu­(III) ion, the positions of the nearest oxygen atoms around the Eu­(III) ion are shifted by steric repulsion and the relative positions of the nearest oxygen atoms are distorted. The distorted coordination environment induces asymmetry in the ligand field, increasing ΦLn and ΦET. ΦTOT is enhanced by the DPDB ligand because it is the product of ΦLn and ΦET. Photoluminescence intensity increases because of the enhanced ΦTOT.

Magnetic and Luminescent Dual Responses of Photochromic Hexaazamacrocyclic Lanthanide Complexes

“…When excited at 365 and 466 nm, the single-exponential decay lifetimes are 1.443 and 1.431 ms, respectively, indicating that decay lifetimes of 1-Eu remain nearly unchanged during the UV light irradiation. To analyze the ligand-to-Eu III energy transfer efficiency (η sens ), the data were calculated by using the equation Q L Eu = η sens × Q Eu Eu = η sens × (τ obs /τ rad ). − In terms of the radiative lifetime (τ rad ) of Eu ( 5 D 0 ), it was calculated according to the formula 1/τ rad = A 0→1 × n 3 × ( I tot / I 0→1 ). The details of all parameters are shown in Table S11.…”

Photoluminescence Properties of Eu(III) Complexes with Two Different Phosphine Oxide Structures and Their Potential uses in Micro-LEDs, Security, and Sensing Devices: A Review

“…(Tris{6,6,7,7,8,8,8-heptafluoro-1-[2-(9,9dimethylfluorenyl)]-1,3-octanedionate} europium(III) (Eu(III)(hfod) 3 ) (Figure 12) [26].…”

“…The norm of the effective dipole moment of the ligand field μ was defined [26]. We demonstrated that the energy transfer efficiencies from the lowest triplet state of the ligands to the 5 D 1 level of the Eu(III) ion (Φ ET ) increases when the ligand fields of the Eu(III) ion become more asymmetric by coordinating the DPDB ligand.…”

Discovering of the L ligand impact on luminescence enhancement of Eu(Dibenzoylmethane)3.Lx complexes employing transient absorption spectroscopy

“…This ratio can be used as a qualitative measure of the local symmetry around the europium ion in the complex. That is because &'& depends mainly on the band area for the 0 5 → 7 $ 2 transition, which is extremely sensitive to the symmetry of the complex [32,33]. In this equation is the refractive index of the medium and 0 5 → 7 $ 1 is spontaneous emission probability for 0 5 → 7 $ 1 transition in vacuo(calculated [31] to be 14.65 s -1 ).Given that these ratios are virtually equal we calculate almost identical values for Eu(III) complexes in solution (Table 1).…”