Stable Pincer Gold(III)-TADF Emitters with Extended Donor–Acceptor Separation for Efficient Vacuum-Deposited OLEDs with Operational Lifetime (LT95) up to 3831 h at 1000 cd m−2

Abstract

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 S1 and T1 excited states, thus narrowing the singlet–triplet energy gap (ΔEST). The combination of small ΔEST 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 (kr up to 106 s−1), 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 (EQEmax) of up to 22.2%, and ii) a record- long operational lifetime (LT95) of 3831 h at an initial luminance of 1000 cd m−2. This excellent durability makes the pincer gold(III)-TADF emitter a promising and competitive alternative to iridium and platinum emitters for practical OLED applications.