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.