Abstract
A set of Sc, Nd, Sm, Eu, Ho, Gd, Er, Yb complexes with perfluorinated 2-(benzothiazol-2-yl)phenolate ligands Ln(SONF)3(DME) were synthesized by the reactions of silylamides Ln[N(SiMe3)2]3 with phenol H(SONF). The structure of the initial phenol, Sc, and Er complexes was established using X-ray analysis, which revealed that the obtained compounds are mononuclear, in contrast to the binuclear non-fluorinated analogues [Ln(SON)3]2 synthesized earlier. All the obtained complexes, both in solid state and in tetrahydrofuran (THF) solutions, upon excitation by light with λex 395 or 405 nm show intense luminance of the ligands at 440–470 nm. The Eu complex also exhibits weak metal-centered emission in the visible region, while the derivatives of Sm luminesces both in the visible and in the infrared region, and Nd, Er, and Yb complexes emit in the near IR (NIR) region of high intensity. DFT (density functional theory) calculation revealed that energy of frontier orbitals of the fluorinated complexes is lower than that of the non-fluorinated counterparts. The level of highest occupied molecular orbital (HOMO) decreases to a greater extent than the lowest occupied molecular orbital (LUMO) level.
Highlights
The search for new efficient photo- and electroluminophores still remains an urgent task
Near infrared (NIR) luminescence, especially from lanthanide complexes, such as Nd3+ and Yb3+, has emerged as an area of paramount interest due to its pioneering technological applications in fields ranging from bioimaging to optical communications [1,2,3,4,5,6,7]
3)2]3 were synthesized to the procedure published elsewhere [54]. 2- was to thecomplexes known procedure
Summary
The search for new efficient photo- and electroluminophores still remains an urgent task. Since f-f transitions are largely forbidden, the ligand-free Ln3+ ions have very low molar absorption coefficients and the direct excitation of lanthanide ions always leads to modest or low luminescent intensities [8,9,10,11,12,13,14,15]. This problem can be solved with the help of organic ligands, which harvest excitation energy and transfer it to the attached Ln3+ ion, significantly increasing its luminescence (antenna effect) [16,17,18,19].
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