Circularly Polarized Luminescence in Enantiopure Europium and Terbium Complexes with Modular, All-Oxygen Donor Ligands

Abstract

Circulaly polarized luminescence from terbium(III) complexed and excited by chiral antenna ligands gives strong emissionThe modular synthesis of three new octadentate, enantiopure ligands are reported -one with the bidentate chelating unit 2-hydroxyisophthalamide (IAM) and two with 1-hydroxy-2-pyridinone (1,2-HOPO) units. A new design principle is introduced for the chiral, non-racemic hexamines which constitute the central backbones for the presented class of ligands. The terbium(III) complex of the IAM ligand, as well as the europium(III) complexes of the 1,2-HOPO ligands are synthesized and characterized by various techniques (NMR, UV, CD, luminescence spectroscopy). All species exhibit excellent stability and moderate to high luminescence efficiency (quantum yields Φ Eu = 0.05-0.08 and Φ Tb = 0.30-0.57) in aqueous solution at physiological pH. Special focus is put onto the properties of the complexes in regard to circularly polarized luminescence (CPL). The maximum luminescence dissymmetry factors (g lum ) in aqueous solution are high with |g lum | max = 0.08 -0.40. Together with the very favorable general properties (good stability, high quantum yields, long lifetimes), the presented lanthanide complexes can be considered as good candidates for analytical probes based on CPL in biologically relevant environments.

Structural and Photophysical Properties of Visible- and Near-IR-Emitting Tris Lanthanide(III) Complexes Formed with the Enantiomers of N,N′-Bis(1-phenylethyl)-2,6-pyridinedicarboxamide

“…27, 28, 38, 71, 72 On the other hand, one would have expected that the CPL would have been dependent on the excitation polarization if the solution would have contained a mixture of diastereoisomers. 73, 74 This is also in good agreement with the X–ray crystal structures of [Ln L 3 ] 3+ (Ln(III) = Eu, Gd, Tb, Yb and L = ( R , R )– 1 and ( S , S )– 1 ) showing the formation of triple helical complexes in the solid state (see below). In summary, the apparent easy formation of the 1:3 species contrasts with what was observed with L 8 , 58 and confirms that L is not blocked in the syn , syn , ZZ conformation.…”

Strong Circularly Polarized Luminescence from Highly Emissive Terbium Complexes in Aqueous Solution

“…Additionally, the g lum values obtained for this complex are the same upon excitation with right-, left-, and plane-polarized light, which is consistent with the presence of only one species in solution;[23] had the solution contained a mixture of diastereomers, the CPL signal would have been dependent on the polarization of the excitation beam. [24] In contrast, the g lum values obtained for dpenLI-Tb are dependent on the polarization of the excitation beam and on whether direct or indirect excitation is used, which indicates that more than one species in solution is responsible for the CPL signal detected. These results support the lifetime data, which indicate the presence of two emitting species in solution that differ in hydration number and therefore also coordination environment.…”

Lanthanide Circularly Polarized Luminescence: Bases and Applications

“…The same structural motif was employed to develop similar ligands, designed to provide a bigger steric hindrance and shield the Ln 3+ ion from water coordination in a more effective way. 37…”