High Radiative Rate and Brightness Electroluminescent Cu(I) Complexes via Carbene‐Induced Electronic Coupling Enhancement

Carbene‐metal‐amides (CMAs), a class of luminescent Cu(I) complexes, are considered a promising low‐cost alternative to Ir and Pt‐based organic light‐emitting diode (OLED) emitters. Although the modular design of the compounds enables easy adjustment of photophysical properties through ligand substitution, the limited understanding of the carbene fragment's impact on light emission characteristics constrains material optimization. Here, we reveal that in CMAs the expansion of the π‐electronic system of the carbene moiety and the increase in its aromaticity strengthen the emissive charge‐transfer (CT) transitions. Following this principle, three complexes incorporating novel benzo[d]thiazol‐2‐ylidene (Btz) carbene ligand are synthesized. The obtained CMAs achieve a record‐high fluorescence rate of 4.81×10 7 s −1 , enabling fast and efficient thermally activated delayed fluorescence (TADF) emission with radiative rates up to 1.4×10 6 s −1 and photoluminescence yield up to 0.99. Furthermore, expansion of the π‐electron system of the carbene ligand evenly distributes negative charge across its surface, improving the stability of emitters in the excited state. This enables the development of OLED devices with an external quantum efficiency of 15.2% and exceptionally high maximum brightness exceeding 100,000 cd m −2 . The presented results provide valuable guidelines for further improvement of CMA emitters by clarifying the photophysical significance of the carbene ligand.