Modular enhancement of circularly polarized luminescence in Pd(2)A(2)B(2) heteroleptic cages

Metal-mediated assembly allows us to combine an achiral emissive ligand A with different chiral ligands (such as B) in a non-statistical fashion, obtaining Pd(2)A(2)B(2) heteroleptic cages showing circularly polarized luminescence (CPL). By using the ‘shape complementary assembly’ (SCA) strategy, the cages are exclusively obtained as cis-Pd(2)A(2)B(2) stereoisomers, as confirmed by NMR, MS and DFT analyses. Their unique chiroptical properties derive from the synergy of all the building blocks. Ligand B imparts the chiral information of its aliphatic backbone, comprising two stereogenic sp(3) carbon centres, to the overall structure, causing CD and CPL signal induction for the chromophore on ligand A. The heteroleptic cage shows CPL with a |g(lum)| value of 2.5 × 10(−3), which is 3-times higher than that for a progenitor based on aromatic helical building block H, thus opening a rational route towards optimizing the CPL properties of self-assembled nanostructures in a modular way.