Luminescent Complexes of Europium (III) with 2-(Phenylethynyl)-1,10-phenanthroline: The Role of the Counterions

Abstract

New antenna ligand, 2-(phenylethynyl)-1,10-phenanthroline (PEP), and its luminescent Eu (III) complexes, Eu(PEP)2Cl3 and Eu(PEP)2(NO3)3, are synthesized and characterized. The synthetic procedure applied is based on reacting of europium salts with ligand in hot acetonitrile solutions in molar ratio 1 to 2. The structure of the complexes is refined by X-ray diffraction based on the single crystals obtained. The compounds [Eu(PEP)2Cl3]·2CH3CN and [Eu(PEP)2(NO3)3]∙2CH3CN crystalize in monoclinic space group P21/n and P21/c, respectively, with two acetonitrile solvent molecules. Intra- and inter-ligand π-π stacking interactions are present in solid stat and are realized between the phenanthroline moieties, as well as between the substituents and the phenanthroline units. The optical properties of the complexes are investigated in solid state, acetonitrile and dichloromethane solution. Both compounds exhibit bright red luminescence caused by the organic ligand acting as antenna for sensitization of Eu (III) emission. The newly designed complexes differ in counter ions in the inner coordination sphere, which allows exploring their influence on the stability, molecular and supramolecular structure, fluorescent properties and symmetry of the Eu (III) ion. In addition, molecular simulations are performed in order to explain the observed experimental behavior of the complexes. The discovered structure-properties relationships give insight on the role of the counter ions in the molecular design of new Eu (III) based luminescent materials.

Molecular Design of Luminescent Complexes of Eu(III): What Can We Learn from the Ligands

“…This, in addition to the fact that the 5 D 0 → 7 F 0 transition is only 0.2% of the whole emission spectrum, is a clear indication of the high symmetry of the complex [ 28 ]. The measured emission quantum yield in acetonitrile is 24.15% ± 0.36%, which is significantly higher than the results obtained previously for other Eu(III) complexes, synthesized in our group with 2-(phenylethynyl)-1,10-phenanthroline [ 25 ]. Such improvement of the quantum yield can be explained by the higher in energy triplet excited state in the case of the L5 ligand with respect to the previously reported antenna—2-(phenylethynyl)-1,10-phenanthroline.…”

“…The ground states of the isolated ligands and their corresponding complexes of type Eu(L) 2 A 3 (where A = Cl − or NO 3 − ) are optimized with the ωB97xD functional [ 24 ]. The initial atomic coordinates used for geometry optimizations of the complexes are taken from the crystallographic data for structurally similar Eu(III)-complexes synthesized recently by our group [ 25 ]. The Pople’s 6-31G* basis set is used for all non-metal elements.…”

“…The complex was prepared by the procedure described in [ 25 ]. Eu(NO 3 ) 3 ∙5H 2 O and the ligand were dissolved in acetonitrile and mixed at 80 °C.…”

“…Our computational study is performed with the TD-DFT method within the Tamm-Dancoff (TDA) approximation [ 23 ] and the ωB97xD functional [ 24 ]. It was already demonstrated that this theoretical approach successfully explores the structure and the photophysical properties of complexes containing rare earth metals because it reduces the problems arising from triplet instability [ 25 , 26 ]. The novelty of our computational study is that it reveals a simple quantitative relationship between the HOMO-LUMO gap of the isolated phenanthroline ligands and the excitation energy to the first triplet excited state of the complexes, which allows quick computational prediction of the luminescent properties of similar compounds.…”

Efficient Synthesis of Fluorescent Coumarins and Phosphorous-Containing Coumarin-Type Heterocycles via Palladium Catalyzed Cross-Coupling Reactions

“…Most reactions with the chosen substrates were performed under classical conditions for Sonogashira coupling [ 55 , 56 ]—Pd(PPh 3 ) 2 Cl 2 /CuI as a catalytic system in the presence of Et 3 N in DMF at 80 °C under argon atmosphere. To compensate the electron-rich nature of the 4-ethynylanisole, entry 4 , Table 6 , PEPPSI-type complex was applied.…”