Eu3+ and Tb3+ coordination compounds with phenyl-containing carbacylamidophosphates: comparison with selected Ln3+ β-diketonates

Abstract

Materials based on Eu3+ and Tb3+ coordination compounds are of great interest due to their strong red and green luminescence. Appropriate selection of ligands plays a huge role in optimizing their photophysical properties. Another very helpful instrument for such optimization is theoretical modelling, which permits the prediction of the emissive properties of materials through intramolecular energy transfer analysis. The ligands that allow for achieving high efficiency of Eu3+ and Tb3+ emissions include carbacylamidophosphates (CAPh, HL). In this brief review, we summarize recent research for lanthanides CAPh-based coordination compounds of general formulas Cat[LnL]4, [LnL3Q] and [Ln(HL)3(NO3)3], where Cat+ = Cs+, NEt4+, PPh4+ and Q = 1,10-phenanthroline, 2,2-bipyridine or triphenylphosphine oxide, involving the use of thermal gravimetric analysis, X-ray analysis, and absorption and luminescence spectroscopy. We carried out a comparison with selected Ln3+ β-diketonates. Possibilities and developments of theoretical calculations on energy transfer rates are also presented.

Structure, Thermal Properties and Photoluminescence of Terbium and Dysprosium Mixed‐Ligand Complexes with Dimethyl‐N‐Trichloroacetylamidophosphate and 2,2’‐Bipyridine

“…The emission lifetime was measured by monitoring the most intense terbium transition 5 D 4 → 7 F 5 and was found to be equal to 2.0–2.2 ms, depending on the excitation wavelength (320 and 290 nm, respectively). The obtained values are among the highest values known for mixed‐ligand CAPh‐based tris ‐complexes [17,28,39] and significantly higher compared to mixed‐ligand terbium complexes with β‐diketones [40–42] . This could be due to reduced high energy vibrations in the chelating fragment of the CAPh compared to β‐diketones.…”

“…Several exited states of Dy III ion ( 5 G 11/2 , 5 I 15/2 , and emitting level 4 F 9/2 ) can receive energy from organic ligands, while for the terbium complex the receiving state is exactly an emitting level 5 D 4 . It is interesting to note, that bipy's lowest triplet state is not constant in complexes [Ln(CAPh) 3 bipy] and varies within 22810 to 23809 cm −1 for the reported compounds of this type [17,21,39] . These differences could be due to varying intermolecular interactions depending on CAPh ligand as well as they indicate that some intramolecular coupling between the two ligand chromophores takes place in the mixed chelate.…”

“…This could be due to reduced high energy vibrations in the chelating fragment of the CAPh compared to β‐diketones. The dependence of lanthanides luminescence lifetime upon excitation wavelength is a widespread phenomenon [17,43] . The CIE coordinates x, y for [Tb(L) 3 bipy] equal 0.334, 0.594, which corresponds to the green color of emission (Figure 4).…”

“…Among the ligands suitable for sensitization of Tb III and Dy III luminescence there are carbacylamidophosphates – P,N‐substitutes of β‐diketones [17] , and 2,2’‐bipyridine, the energy of the excited triplet state of which was shown to be near 23 000 cm −1 [18] . The structure of CAPhs is organized in such a way as to reduce the high energy vibrations in the chelating fragment.…”

“…The structure of CAPhs is organized in such a way as to reduce the high energy vibrations in the chelating fragment. Moreover, CAPh‐based coordination compounds of lanthanides are thermally and photo‐stable [17,19] . The europium and samarium complexes of general formula [Ln(L) 3 bipy] have been earlier obtained and shown to be good emitters of red and orange light, respectively [20,21] .…”