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

Abstract

Two luminescent terbium(III) complexes have been prepared from chiral ligands containing 2-hydroxyisophthalamide (IAM) antenna chromophores and their non-polarized and circularlypolarized luminescence properties have been studied. These tetradentate ligands, which form 2:1 ligand/Tb III complexes, utilize diaminocyclohexane (cyLI) and diphenylethylenediamine (dpenLI) backbones, which we reasoned would impart conformational rigidity and result in Tb III complexes that display both large luminescence quantum yield (Φ) values and strong circularly polarized luminescence (CPL) activities. Both Tb III complexes are highly emissive, with Φ values of 0.32 (dpenLI-Tb) and 0.60 (cyLI-Tb). Luminescence lifetime measurements in H 2 O and D 2 O indicate that while cyLI-Tb exists as a single species in solution, dpenLI-Tb exists as two species: a monohydrate complex with one H 2 O molecule directly bound to the Tb III ion and a complex with no water molecules in the inner coordination sphere. Both cyLI-Tb and dpenLI-Tb display increased CPL activity compared to previously reported Tb III complexes made with chiral IAM ligands. The CPL measurements also provide additional confirmation of the presence of a single emissive species in solution in the case of cyLI-Tb, and multiple emissive species in the case of dpenLI-Tb.

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

“…This was consistent with the presence of only one diastereomeric species in solution. 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).…”

Lanthanide Probes for Bioresponsive Imaging

“…19,70,71 Coordination of IAM occurs through the phenolate oxygen and the adjacent carbonyl oxygen (salicylate-type binding as shown in Figure 4B, top left). The amide of the other carbonyl forms a hydrogen bond with the phenolic oxygen and stabilizes a favorable ligand conformation for metal coordination.…”

Lanthanide Circularly Polarized Luminescence: Bases and Applications

“…1, concerning the 5 D 4 → 7 F 5 transition of a Tb 3+ chiral complex. 27 Clearly, when this happens, total emission and CPL bands do not coincide in general and special care should be taken in evaluating the g lum value.…”

“…Ln 3+ transitions generally observed in CPL measurements with their D class22 and their approximate wavelength CPL and total emission of a Tb 3+ complex for 5 D 4 → 7 F 5 transition. Notice how the manifold is resolved in the CPL spectrum (reproduced with permission from Ref 27…”