Stable Pincer Gold(III)-TADF Emitters with Extended Donor-Acceptor Separation for Efficient Vacuum-Deposited OLEDs with Operational Lifetime (LT) up to 3831 h at 1000 cd m.

Although gold-TADF (thermally activated delayed fluorescence) emitters have attractive prospects as next-generation practical OLED emitters, the performance of OLEDs utilizing gold(I)- and gold(III)-TADF emitters lags behind the requirements of practical applications, and device lifetime has become a bottleneck. Here, novel pincer gold(III)-TADF emitters that are easily fabricated with tunable donor and acceptor ligands are presented. These pincer gold(III)-TADF emitters exhibit an extended molecular π-distance along the transition dipole moment, resulting in a significant reduction in the electron exchange energy between the S and T excited states, thus narrowing the singlet-triplet energy gap (ΔE). The combination of small ΔE and heavy-atom (Au, S) effect greatly enhances spin-flip dynamics and produces efficient TADF (photoluminescence quantum yields up to 90%) with high radiative decay rate constants (k up to 10 s), and short lifetimes (τ less than 1.2 µs) in thin films at room temperature. Vacuum-deposited OLEDs based on these gold(III)-TADF emitters demonstrate impressive stability, achieving i) a high maximum external quantum efficiency (EQE) of up to 22.2%, and ii) a record- long operational lifetime (LT) of 3831 h at an initial luminance of 1000 cd m. This excellent durability makes the pincer gold(III)-TADF emitter a promising and competitive alternative to iridium and platinum emitters for practical OLED applications.