Breaking the Excitation Barrier: Visible-Light-Harvesting Ir(III)-Eu(III) Dyads for Circularly Polarized Luminescence and Theranostics

Abstract

The application of lanthanide-based circularly polarized luminescence (CPL) probes in biological systems has long been impeded by a fundamental trade-off: the need for high-energy ultraviolet excitation to overcome the low absorptivity of f-f transitions versus the phototoxicity and poor tissue penetration inherent to UV irradiation. Herein, we resolve this "excitation bottleneck" by engineering a heteronuclear Ir(III)-Eu(III) dyad that functions as a highly efficient, visible-light-harvesting CPL generator. By exploiting the broad metal-to-ligand charge transfer (MLCT) absorption of a cyclometalated Ir(III) antenna, we successfully red-shift the excitation window to the benign visible region (λex > 425 nm), extending up to ∼500 nm. This sensitization strategy yields intense red Eu(III)-based emission with a substantial luminescence dissymmetry factor (|glum| = 0.114) without requiring deleterious UV light. Capitalizing on this visible-light accessibility and the kinetic inertness of the rigid DO3A scaffold, we demonstrate dual-modal one-and two-photon confocal imaging in living cells. Furthermore, the dyad exhibits efficient singlet oxygen generation (Φ∆ = 0.82), enabling photodynamic therapy. This work establishes a versatile paradigm for visible-light-driven lanthanide chiroptics, effectively bridging the gap between superior chiral photophysical properties and biocompatible excitation requirements.