Synergistic Complexation of Eu³⁺by a Polydentate Ligand and a Bidentate Antenna to Obtain Ternary Complexes with High Luminescence Quantum Yields

Abstract

A series of ternary Eu 3+ complexes are presented consisting of a polydentate m-terphenyl-based Eu 3+ complex (Eu)1 and different antenna chromophores possessing lanthanide(III) ion coordinating properties. The series of investigated antenna chromophores consist of 1,10-phenanthroline, tetraazatriphenylene, and three β-diketonates, namely dibenzoylmethane, benzoyltrifluoroacetylacetonate, and hexafluoroacetylacetonate. As a result of the synergistic complexation of Eu 3+ by the polydentate ligand and the bidentate antenna, the distance between the antenna and lanthanide ion has been minimized and the Eu 3+ ion has been shielded completely from the solvent. These are two important requirements to obtain efficiently emitting lanthanide-(III) complexes. The formation of the ternary complexes and their photophysical properties, in particular the population of the Eu 3+ excited states and the efficiency of the sensitization process, have been studied in detail. Based on these measurements, it can be concluded that the aforementioned strategy of synergistic complexation has indeed led to the construction of efficiently emitting Eu 3+ complexes. The β-diketonate ternary Eu 3+ complexes combine a high stability (K ) 3.8 ( 0.2 × 10 7 M -1 ) with high overall luminescence quantum yields of up to 0.29. The energy transfer from the sensitizer to the Eu 3+ is exclusively to the 5 D 1 level, from which the 5 D 0 level is populated.

Sensitized Emission of Luminescent Lanthanide Complexes Based on 4‐Naphthalen‐1‐yl‐Benzoic Acid Derivatives by a Charge‐Transfer Process

“…Also, [(Eu)1]bfa has a higher quantum efficiency than that of [(Eu)1]hfa, in which the energy difference is 3000 and 2400 cm À1 for [(Eu)1]hfa and [(Eu)1]bfa, respectively. [18] In summary, we suggest that the slightly lowered quantum efficiency in NAC-2 may be due to back energy transfer and a smaller spectral overlap integral (J).…”

“…To obtain an effective energy transfer between the singlet luminescent ligand and the lanthanide ion, the emission energy level of the ligands should overlap well with the absorption energy level of the Eu III ion. [18] The energy level of the Eu III ion for the highest oscillation strength of its absorption bands is estimated to be 25 300 cm À1 and overlaps well with the singlet excite state of NA-2 (25 000 cm…”

Aryl-Bridged 1-Hydroxypyridin-2-one: Sensitizer Ligands for Eu(III)

“…4 Unfortunately, for the same reason, the molar absorption coefficient of lanthanide transitions is very small (less than 10 M −1 .cm −1 ). 5 To obviate this problem, organic ligands having a large molar absorption coefficient can be coordinated to the lanthanide ion, resulting in sensitized emission through the so-called antenna effect. The mechanism of antenna sensitization is comprised of three differing steps: the initial excitation of the ligand, followed by intersystem crossing to give an excited triplet state, then subsequent energy transfer to yield the metal centered excited state which emits light.…”

Facilitated Energy Transfer in Hierarchically-Ordered Polymers

“…This suggests that conformational mobility of the methoxy groups is hindered as the dendrons increase in size, a result in accord with previous studies. 23 In addition to this decrease in T 1 values, there are two distinguishable methoxy proton signals for the G2 and G3 dendrimers, indicating that there are methoxy protons in two different chemical environments. These two signals integrate to a 2:1 ratio.…”

“…The emission spectrum for [(G2)BTFA] 3 Eu, shown in Figure 7c, F J transitions of trivalent europium can be deconvoluted from the 5 D 0 → 7 F J transitions using a pulsed laser system and streak camera. 23 Emissions from the former transitions are much lower in intensity than those from the latter transitions. Also, the 5 D 0 state decays in the order of milliseconds, while the 5 D 1 state decays in the order of microseconds.…”