Green light-emitting electrochemical cells based on platinum(ii) complexes with a carbazole-appended carbene ligand

Abstract

Platinum(II) complexes bearing new carbazole-appended cyclometallated N-heterocyclic carbenes such as [Pt(Cbz-C^C*)Cl(NCCH₃)](3), [Pt(Cbz-C^C*)Cl(PPh₃)](4), [Pt(Cbz-C^C*)(PPh₃)(py)]PF₆ (py = pyridine, 5), [Pt(Cbz-C^C*)(P^N)]PF₆ (P^N = 2-(2-(diphenylphosphino) ethyl) pyridine, 6), and [Pt(Cbz-C^C*)(P^P)]PF₆ (P^P: 1,1-bis(diphenylphosphino)methane, dppm 7; 1,2-bis(diphenylphosphino)ethane, dppe, 8, 1,2-bis(diphenylphosphino) benzene, dppbz, 9) have been prepared using a stepwise procedure from 9-(4-bromo-phenyl)-9H-carbazole, imidazole, [{Pt(μ-Cl)(η³-2-Me-C₃H₄)}₂] and the corresponding ancillary ligands. They have been fully characterized. Also, single-crystal X-ray structures, theoretical calculations and photophysical studies have been performed. These complexes have been employed as emitters in simple solution-processed light-emitting electrochemical cells (LECs). When driven under a pulsed current of 50 A m⁻², devices based on 7–9 exhibited green emission, a luminance of 265 cd m⁻² and a current efficiency of 5.7 cd A⁻¹ (for the best performing emitter, 7). As far as we know, these are the first examples of green-emitting Pt(II)-based LECs.