Abstract
A series of tetrakis-β-diketonate Q+[Ln(β-dik)4]–, where Ln = GdIII or EuIII, Q = ammonium cations and β-dik = tta (2-thenoyltrifluoracetone) or bmdm (1-(4-tert-butylphenyl)-3-(4-methoxyphenyl)-1,3-propanedione) have been synthesized and characterized. The environment surrounding the EuIII ion depends on the lateral groups of the ligand and on the alkyl chains of the counter ion Q. The shortest lifetime (τ) = 0.29 ms, and lowest quantum efficiencies (η) = 24%, were obtained for (N(C12H25)2(CH3)2)+[Eu(bmdm)4]–, while (N(C4H9)4)+[Eu(bmdm)4]– has the longest τ = 1.04 ms and η = 90%. The Judd-Ofelt intensity parameters (Ω2 and Ω4) strongly changes for tta series pointing to stronger ion-dipole interactions between the –CF3 group with the ammonium cations. The agreement between the experimental results of photoluminescence and theoretical data suggests that the geometries optimized by the Sparkle model are correct. These results point to potential candidates for building up Langmuir-Blodgett (LB) luminescent films, since it is possible to maximize the intermolecular interactions and the photoluminescent properties of tetrakis LnIII complexes.
Highlights
The characteristic emission lifetimes in the range μs-ms and the narrow emission bands of the LnIII compounds are very attractive for applications such as displays, sensors and photoluminescent labels in biological systems.[1,2,3,4,5] Due to the Laporte forbidden 4f-4f transitions, the absorption of energy occurs through a sensitizer, called antenna, and transferred to the LnIII that emits in a characteristic wavelength.[6]
The main interest in LnIII-β-diketonate complexes lies in their photoluminescent properties
JO theory has become crucial to evaluating the performance of the luminescent materials in terms of symmetry around EuIII ion.[19,20,21]
Summary
The characteristic emission lifetimes in the range μs-ms and the narrow emission bands of the LnIII compounds are very attractive for applications such as displays, sensors and photoluminescent labels in biological systems.[1,2,3,4,5] Due to the Laporte forbidden 4f-4f transitions, the absorption of energy occurs through a sensitizer (usually an organic ligand), called antenna, and transferred to the LnIII that emits in a characteristic wavelength.[6]. We report the synthesis, characterization and influence of the counterion in the photoluminescent properties of tetrakis EuIII or GdIII complexes with the general formula Q+[Ln(b-dik)4]– (β‐dik = 2-thenoyltrifluoracetone (tta) or 1-(4-tert-butylphenyl)-3-(4-methoxyphenyl)propane1,3-dione (bmdm)) neutralized by different ammonium cations Q (tetraethylammonium, tetrabutylammonium, and didodecyldimethylammonium) containing short, intermediate or long alkyl chain.
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