Fused Cycloalkyl Unit‐Functionalized Tetradentate Pt(II) Complexes for Efficient and Narrow‐Emitting Deep Blue Organic Light‐Emitting Diodes

Abstract

A blue tetradentate Pt(II) complex named Pt‐tmCyCz is developed by introducing a cycloalkyl unit fused to carbazole to improve the rigidity and bulkiness of the complex. The introduction of the tetramethylcyclohexyl (tmCy) group results in a narrow full width at half maximum (FWHM), a high horizontal emitting dipole orientation, doping concentration resistant stable spectrum, and extremely small efficiency roll‐off, and little concentration quenching effect. Phosphorescent organic light‐emitting diodes (OLEDs) doped with Pt‐tmCyCz achieve a high external quantum efficiency (EQE) of 21.5%, with a small EQE roll‐off of 3.8% up to 1000 cd m−2, a small FWHM of 24 nm, and a color coordinate of (0.132, 0.138). Moreover, Pt‐tmCyCz is investigated as a sensitizer in phosphor‐sensitized OLEDs using N7,N7,N13,N13,5,9,11,15‐octaphenyl‐5,9,11,15‐tetrahydro‐5,9,11,15‐tetraaza‐19b,20b‐diboradinaphtho[3,2,1‐de:1′,2′,3′‐jk]pentacene‐7,13‐diamine (νDABNA) as a terminal emitter. The Pt‐tmCyCz:νDABNA device achieves a high EQE of 33.9%, with a small EQE roll‐off of only 8.0% up to 1 000 cd m−2. The results demonstrate that fused tmCy group in carbazole can be an effective building block for the development of high‐performance Pt(II) complexes, which can be utilized as efficient phosphors or sensitizers in OLEDs.

High efficiency and high color purity deep‐blue organic light‐emitting diodes with blue index >500

“…On the contrary, platinum (II)-based phosphors are more prone to intermolecular packing due to the planarity of their molecular structure, accordingly widening the emission spectrum, red-shifting the emission color, and quenching emission. 9 Then, higher energy intrinsic spectrum is required to satisfy the blue color coordinate, which challenges molecular stability. 10 Until now, the high efficiency OLEDs with narrow emission, particularly in the deep-blue region, remain a formidable challenge.…”

“…Molecular vibration and fluctuations can be minimized by the structural rigidity of the tetradentate coordination. On the contrary, platinum (II)‐based phosphors are more prone to intermolecular packing due to the planarity of their molecular structure, accordingly widening the emission spectrum, red‐shifting the emission color, and quenching emission 9 . Then, higher energy intrinsic spectrum is required to satisfy the blue color coordinate, which challenges molecular stability 10 .…”

29‐2: Distinguished Paper: High Efficiency and High Color Purity Deep‐Blue Organic Light‐Emitting Diodes with Blue Index >500

“…Molecular vibration and fluctuations can be minimized by the structural rigidity of the tetradentate coordination. On the contrary, Platinum(II)-based phosphors suffer from intermolecular packing due to the planar nature of their molecular structure, accordingly widening the emission spectrum, red-shifting the emission color, and quenching emission at high doping concentration [6] . Then, higher energy intrinsic spectrum is required to satisfy the blue color coordinate, which challenges molecular stability [7] .…”