Surfing the Color Map with Carbazole‐Appended Cyclometalated N‐Heterocyclic Carbene Pt Complexes and Their Application in Green Organic Light‐Emitting Devices

Abstract This paper describes the stage‐wise synthesis of the new carbazole‐appended platinum (II) cyclometalated N‐heterocyclic carbene complex, [Pt(Cbz‐C^C* bzim )Cl(NCCH 3 )] ( A ) (HC^C* = 1‐(4‐(9H‐carbazol‐9‐yl)phenyl)‐3‐methyl‐1 H ‐benzimidazol‐2‐ylidene) from 9‐(4‐bromo‐phenyl)‐9H‐carbazole, benzimidazole and [{Pt( μ ‐Cl)( ƞ 3 ‐2‐Me‐C 3 H 4 )} 2 ]. Complex A , and the analogous imidazole derivative [Pt(Cbz‐C^C* im )Cl(NCCH 3 )] ( B ), are the precursors of the neutral complexes [Pt(Cbz‐C^C* bzim/im )(acac)] ( 1A/B , acac: acetylacetonate), [Pt(Cbz‐C^C* bzim/im )(P^O 1 )] ( 2A/B , P^O 1 : 2‐diphenylphosphinobenzoate) and [Pt(Cbz‐C^C* bzim/im )(P^O 2 )] ( 3A/B , P^O 2 : 2‐diphenylphosphinophenolate). At low doping concentration in poly(methylmethacrylate (PMMA) films (1% for 1A/B and 5% for 2A/B and 3A/B ), they show a bright phosphorescent emission, peaking in the blue ( 1B ‐ 3B ) or blue–green ( 1A ‐ 3A ) spectral range. The planar structure of 1A and 1B enables intermolecular interactions, especially for 1A , with a more extended π–system, which changes the color from blue to yellowish–green at higher doping concentration. Organic Light‐Emitting Diodes (OLEDs) using 1A and 1B as emitters in thick doped and in ultrathin non‐doped emitting layers show aggregate‐derived emission even at very low concentrations. The best performing devices in this work use 1A and 3A and show a turn‐on voltage of 2.99 and 2.55 V, a peak luminance of 39208 and 25837 cd m −2 , and a peak current efficiency of 44.9 and 40.0 cd A −1 (12.8% and 13.4% EQE).