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

We describe the synthesis of C-2-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, lambda(exc) 295 nm, lambda(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.