Effective Near-Infrared Triplet Emitter Based on Hetero-Metal–Metal Interaction

Incorporating metal-metal (M-M) interactions into excited states of closed-shell d⁸ and d¹⁰ metal complexes is an effective strategy in the design of near-infrared (NIR) phosphorescent materials. While extensive studies have focused on homometallic M-M-bonded excited states, the potential of heterometallic interactions remains relatively underexplored. Herein, we report a series of heterometallic Rh(I)-Pt(II) double salt complexes that achieve efficient NIR phosphorescence, with emission peak energy spanning 830-980 nm and room-temperature quantum yield up to 23%. In this system, the Rh(I) center lowers the emission energy, while the Pt(II) center enhances spin-orbit coupling (SOC) via its heavy-atom effect. The resulting materials exhibit an outstanding waveguiding performance in the NIR spectral region. Combined spectroscopic and time-dependent density functional theory (TDDFT) analyses reveal that the Rh(I)-Pt(II) interaction directly modulates the excited state character, enhancing the radiative decay while suppressing nonradiative decay pathways. This work establishes heterometallic M-M cooperativity as a design principle for high-performance NIR phosphorescence, opening avenues for tailored NIR phosphorescent materials beyond conventional homometallic frameworks.