Highly Luminescent, Water‐Soluble Lanthanide Fluorobenzoates: Syntheses, Structures and Photophysics, Part I: Lanthanide Pentafluorobenzoates

Abstract

Highly luminescent, photostable, and soluble lanthanide pentafluorobenzoates have been synthesized and thoroughly characterized, with a focus on Eu(III) and Tb(III) complexes as visible emitters and Nd(III) , Er(III) , and Yb(III) complexes as infrared emitters. Investigation of the crystal structures of the complexes in powder form and as single crystals by using X-ray diffraction revealed five different structural types, including monomeric, dimeric, and polymeric. The local structure in different solutions was studied by using X-ray absorption spectroscopy. The photoluminescence quantum yields (PLQYs) of terbium and europium complexes were 39 and 15 %, respectively; the latter value was increased almost twice by using the heterometallic complex [Tb0.5 Eu0.5 (pfb)3 (H2 O)] (Hpfb=pentafluorobenzoic acid). Due to the effectively utilized sensitization strategy (pfb)(-) →Tb→Eu, a pure europium luminescence with a PLQY of 29 % was achieved.

Lanthanide Fluorobenzoates as Bio‐Probes: a Quest for the Optimal Ligand Fluorination Degree

“…[36][37][38][39][40] The first one is an exchange reaction between an aqueous solution of an alkali metal carboxylate and al anthanide inorganic salt, [37,40] and the second one is the interaction of af reshly preparedl anthanide hydroxide with as olution of carboxylic acid. [36][37][38][39][40] The first one is an exchange reaction between an aqueous solution of an alkali metal carboxylate and al anthanide inorganic salt, [37,40] and the second one is the interaction of af reshly preparedl anthanide hydroxide with as olution of carboxylic acid.…”

“…[36][37][38][39][40] The first one is an exchange reaction between an aqueous solution of an alkali metal carboxylate and al anthanide inorganic salt, [37,40] and the second one is the interaction of af reshly preparedl anthanide hydroxide with as olution of carboxylic acid. [36] All the complexes Ln-N (N = 1-9) were fully characterized as powders (Table S1), using thermogravimetry (TG), elemental analysis( EA), infra-red spectroscopy by attenuated total reflec-tion (IR ATR), and luminescence spectroscopy.T hey were also analyzed by powder X-Ray diffraction (PXRD), and for some lanthanide complexes single crystals were obtained andc haracterized by means of single-crystal X-Ray diffraction (SC-XRD). Thus, we selected the synthetic approach depending on the water solubility of the formed lanthanide complexes.…”

“…Thei nfluence of substituents wasd iscussed in several publications, [28][29][30] and the introduction of fluorines ubstituents, in particular,t ends to increaset he luminescence efficiency. [31][32][33][34][35] As some of us have shown previously,l igand fluorination increasest he solubility of lanthanide benzoates and reducesl uminescentq uenching, [36,37] but decreases the thermodynamics tability of the carboxylates. [5,[36][37][38][39][40] Thus, stable Eu benzoates show little luminescence, while perfluorobenzoates are luminescent butu nstable.…”

“…[31][32][33][34][35] As some of us have shown previously,l igand fluorination increasest he solubility of lanthanide benzoates and reducesl uminescentq uenching, [36,37] but decreases the thermodynamics tability of the carboxylates. [5,[36][37][38][39][40] Thus, stable Eu benzoates show little luminescence, while perfluorobenzoates are luminescent butu nstable. [36] We aim to find am iddle groundh ere, that is, the optimum fluorination degree to obtainp hotostable, non-toxic, and luminescentc ompounds suitable for use as bio-probes.…”

“…[5,[36][37][38][39][40] Thus, stable Eu benzoates show little luminescence, while perfluorobenzoates are luminescent butu nstable. [36] We aim to find am iddle groundh ere, that is, the optimum fluorination degree to obtainp hotostable, non-toxic, and luminescentc ompounds suitable for use as bio-probes.…”