Adsorption of Chiral Ir(III) Complexes on Clay Nanosheets: Optical-Purity-Dependent Packing and Amplified Circularly Polarized Luminescence

Abstract Controlling the spatial distribution of photoluminescent molecules within constrained microenvironments remains a fundamental challenge in enhancing their photophysical properties. Herein, we demonstrate that the differential adsorption behavior of enantiopure and racemic octahedral iridium(III) complexes on clay nanosheets can be exploited to modulate their photophysical and chiroptical properties, particularly circularly polarized luminescence (CPL). Two structurally related chiral complexes, [Ir(ppy)2(phen)](PF6) (Ir1-PF6) and [Ir(piq)2(phen)](PF6) (Ir2-PF6), were investigated. Upon adsorption onto colloidal clay, the pseudo-C3-symmetric Ir1+ cation exhibited UV–vis, photoluminescence (PL), and electronic circular dichroism (ECD) spectra distinctly different from those in solution, a phenomenon absent for the sterically bulkier Ir2+ complex. Crucially, Ir1+ displayed distinct photophysical properties between its enantiopure and racemic forms, stemming from contrasting, optical-purity-dependent packing modes. While the racemate was proposed to form stable heterochiral pairs irrespective of loading density, the enantiopure complex underwent dense packing and concentration quenching at higher loadings. Furthermore, despite having the same absolute configuration, Ir1+ and Ir2+ exhibited opposite CPL signs in solution─an inversion computationally attributed to ligand-dependent changes in orbital topologies. Upon confinement within the clay matrix, the CPL intensity of enantiopure Ir1+ was significantly amplified, whereas that of Ir2+ decreased. This enhancement of the CPL intensity of Ir1+ upon clay adsorption closely parallels the effects of cryogenic cooling. Furthermore, all-atom molecular dynamics (MD) simulations revealed that Ir1+ adsorbs closer to the clay surface and directs its ligands toward the hexagonal surface cavities more effectively than Ir2+, that opposite-handed enantiomers of the racemate interact strongly in both cases, and that the bulkier Ir2+, experiencing weaker electrostatic repulsion, tends to aggregate─consistent with the experimental results. These findings establish clay nanosheets as powerful structural scaffolds for transforming weakly emissive molecules into highly functional chiral luminescent materials.