Bright and Stable Electrochemiluminescence by Heterobimetallic Ir ^III ‐M ^I (M ^I = Cu ^I , Au ^I ) Complexes

Abstract Ionic transition metal complexes (iTMCs) often suffer from low photoluminescence quantum yield, especially in the red to near‐infrared spectral region. Rational molecular design strategies unlock recovering the emission features efficiently. A potential solution is offered by bimetallic complexes, which are rapidly emerging as a valid and attractive class of emitters. In this work, the yet unexplored electrochemiluminescence (ECL) properties of a series of heterobimetallic complexes of general structure Ir ^III ‐M ^I are investigated, where the formally neutral cyclometalated iridium complex provides efficient photo‐ and electro‐active properties to the molecular emitters. Whereas bulky M ^I (gold or copper) metalloligand increases structural rigidity and chemical stability of the architecture while enabling larger values for the radiative rate constant. The Ir ^III ‐M ^I shows highly efficient red ECL at λ _{em , max} = 600 nm, which is stable in a wider range of applied potential. The activation is triggered at 0.45–0.65 V, ca. 0.3–0.5 V lower than that of tris ‐(2,2′‐bipyridyl) ruthenium(II) complex, [Ru(bpy) ₃ ] ²⁺ . Remarkably, the ECL quantum yield relative to [Ru(bpy) ₃ ] ²⁺ is up to six‐fold higher, thus positioning this new series of iTMCs amongst the brightest ECL‐active emitters to date and possibly offering a platform to develop novel and even more efficient ECL probes for biosensing and bioimaging applications.