Rational Design of Rigid Chiral Ir(III)–Eu(III) Dyads: Intense Circularly Polarized Luminescence via Visible-Light Sensitization

The utility of lanthanide-based circularly polarized luminescence (CPL) probes in biological systems is frequently limited by kinetic lability and excitation-related toxicity. To overcome these barriers, we have engineered rigid chiral Ir(III)-Eu(III) dyads (Ir-Eu-R and Ir-Eu-S) using a stereoselective ″complex-as-ligand″ strategy. This architecture features a kinetically inert DO3A macrocycle (1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) that effectively preserves the stereochemical environment, yielding intense CPL (|glum| = 0.12) with substantial brightness (BCPL ≈ 8 M⁻¹ cm⁻¹). Simultaneously, the integrated Ir(III) antenna enables benign visible-light sensitization (λex = 425 nm), facilitating low-phototoxicity confocal imaging in HeLa cells. Crucially, the probe's structural rigidity ensures exceptional stability against biological interferents; spectroscopic titration with ct-DNA confirms the preservation of chiroptical signals without conformational distortion. This work presents a general coordination strategy for constructing robust, bright, and visible-light-excitable rare-earth chiroptical materials, opening new avenues for specific chiroptical bioimaging and enantioselective sensing applications.