Sterically Hindered Tetradentate [Pt(O^N^C^N)] Emitters with Radiative Decay Rates up to 5.3 × 10<sup>5</sup> s<sup>−1</sup> for Phosphorescent Organic Light‐Emitting Diodes with LT<sub>95</sub> Lifetime over 9200 h at 1000 cd m<sup>−2</sup>
Tsz‐Lung Lam, Huiyang Li, Kaixin Tan, Ziyong Chen, Yu‐Kan Tang, Jun Yang, Gang Cheng, Lei Dai, Chi‐Ming Che
Abstract
Abstract Described here are sterically hindered tetradentate [Pt(O^N^C^N)] emitters ( Pt‐1 , Pt‐2, and Pt‐3 ) developed for stable and high‐performance green phosphorescent organic light‐emitting diodes (OLEDs). These Pt(II) emitters exhibit strong saturated green phosphorescence (λ max = 517–531 nm) in toluene and mCP thin films with emission quantum yields as high as 0.97, radiative rate constants ( k r ) as high as 4.4–5.3 × 10 5 s −1 and reduced excimer emission, and with a preferential horizontally oriented transition dipole ratio of up to 84%. Theoretical calculations show that p ‐(hetero)arene substituents at the periphery of the ligand scaffolds in Pt‐1 , Pt‐2 , and Pt‐3 can i) enhance the spin‐orbit coupling (SOC) between the lower singlet excited states and the T 1 state, and S 0 →S n ( n = 1 or 2) transition dipole moment, and ii) introducing additional SOC activity and the bright 1 ILCT[π(carbazole)→π*(N^C^N)] excited state ( Pt‐2 and Pt‐3 ), which are the main contributors to the increased k r values. Utilizing these tetradentate Pt(II) emitters, green phosphorescent OLEDs are fabricated with narrow‐band electroluminescence (FWHM down to 36 nm), high external quantum efficiency, current efficiency up to 27.6% and 98.7 cd A −1 , and an unprecedented device lifetime (LT 95 ) of up to 9270 h at 1000 cd m −2 under laboratory conditions.