Thermally Stable Donor–Acceptor Type (Alkynyl)Gold(III) TADF Emitters Achieved EQEs and Luminance of up to 23.4% and 70 300 cd m⁻² in Vacuum‐Deposited OLEDs

Abstract

Thermally stable, strongly luminescent gold‐TADF emitters are the clue to realize practical applications of gold metal in next generation display and lighting technology, a scarce example of which is herein described. A series of donor–acceptor type cyclometalated gold(III) alkynyl complexes with some of them displaying highly efficient thermally activated delayed fluorescence (TADF) with Φ up to 88% in thin films and emission lifetimes of ≈1–2 µs at room temperature are developed. The emission color of these complexes is readily tunable from green to red by varying the donor unit and cyclometalating ligand. Vacuum‐deposited organic light‐emitting diodes (OLEDs) with these complexes as emissive dopants achieve external quantum efficiencies (EQEs) and luminance of up to 23.4% and 70 300 cd m−2, respectively.

Tetradentate Gold(III) Complexes as Thermally Activated Delayed Fluorescence (TADF) Emitters: Microwave‐Assisted Synthesis and High‐Performance OLEDs with Long Operational Lifetime

“…Complexes 4 , 7 and 8 , on the other hand, being short‐lived ( τ <2 μs) with large k r (ca. 10 5 –10 6 s −1 ) display emission behaviors that are similar to the reported Au III ‐TADF complexes . Thus, the emission of 4 , 7 , and 8 likely involves TADF.…”

“…On the other hand, the radiative decay rate constants of phosphorescent Au III complexes are usually small as the emissive excited states, being mainly ligand localized, involve only minor metal parentage, which is detrimental in OLED applications because of large efficiency roll‐off . In this regard, OLEDs fabricated with Au I and Au III ‐TADF emitters ( τ <2 μs) have achieved small roll‐off (<10 %) . A recent study suggested that improving the rigidity of emitters could suppress the structural deformation upon S 1 –T 1 transformation thereby reducing the activation energy barrier for reverse intersystem crossing (RISC) and leading to efficient TADF .…”

“…Such performance is among the best of reported Au III ‐OLEDs and comparable to that of Au I ‐OLEDs (Table S17) . The operational lifetime of OLED prepared with 4 has been measured under our laboratory conditions and compared with that of the best pincer Au III ‐acetylide TADF emitter from our previous report under the same device configuration (Table S18). The OLED of 4 exhibited operational lifetime LT 95 of 1.97 h at initial luminance of 10 390 cd m −2 , corresponding to 105 h at 1000 cd m −2 and 5280 h at 100 cd m −2 , which are the best among all reported Au III ‐OLEDs.…”

“…Notably, a high EQE of 22.01 % was maintained at a high luminance of 1000 cd m −2 . Such performance is among the best of reported Au III ‐OLEDs and comparable to that of Au I ‐OLEDs (Table S17) . The operational lifetime of OLED prepared with 4 has been measured under our laboratory conditions and compared with that of the best pincer Au III ‐acetylide TADF emitter from our previous report under the same device configuration (Table S18).…”

“…Nonetheless, the practical applications of luminescent gold complexes remain in the “proof‐of‐concept” stage. Despite the extensive work on luminescent gold complexes over the past decade, examples of gold organic light‐emitting diodes (OLEDs) with performance data close to that of the best iridium‐OLEDs are very rare, and these rare examples were developed only in the past few years (EQEs of Au I and Au III OLEDs up to 27.5 % and 23.8 % respectively) by exploiting the thermally activated delayed fluorescence (TADF) mechanism . The mainstream design of luminescent Au III complexes is the combined use of two or more ligands.…”