Synthesis of bright water-soluble circularly polarized luminescence emitters as potential sensors

Abstract

We describe the synthesis of C₂-symmetrical enantiopure lanthanide complexes (Tb, Eu, Sm, Dy) supported by the decadentate ligand N,N,N′,N′-tetrakis[(6-carboxypyridin-2-yl)methyl]-1,2-diaminocyclohexane (tpadac). The chiral tpadac ligand was designed to protect the lanthanide center from coordination of inner-sphere water molecules resulting in air- and water-stable, and highly luminescent complexes in water. The complexes exhibit strong chiroptical properties, with high dissymmetry factors g_lum (0.11 to 0.25) and CPL brightness B_CPL (up to 245 M⁻¹ cm⁻¹ for Tb, λ_exc 295 nm, λ_em 544 nm) in water. These are the first example of aqueous Sm CPL and second example of aqueous Dy CPL reported to date. The lanthanide complexes obtained gave a reversible CPL response to pH ranging from 6.0 to 8.0. In addition, distinctive CPL responses (including a change in CPL sign) towards toxic cations (Pb²⁺, Cd²⁺, and Mn²⁺) were also observed, demonstrating the potential of our complexes to be used as aqueous probes.