Dinuclear Pt^II Complexes with Strong Blue Phosphorescence for Operationally Stable Organic Light‐Emitting Diodes with EQE up to 23 % at 1000 cd m⁻²

Abstract

Here we describe the synthesis and characterization of a new class of dinuclear Pt II complexes with blue phosphorescence. Bulky N-heterocyclic carbene and tethered bridging ligands were employed to suppress photo-induced structural changes and to improve thermal stability of the complexes. These complexes show mixed 3 IL/ 3 MLCT blue emission ( � 460 nm) with emission quantum yields of up to 0.95, emission lifetimes of as low as 1.3 μs and radiative decay rate constants of up to 7.3 × 10 5 s À 1 in 4 wt % doped PMMA films; the latter is attributed to a 1 MLCT excited state having high metal character (resulting in a large SOC) and a large transition dipole moment, based on DFT calculations. Phosphor-sensitized blue hyper-OLEDs with Commission Internationale de L'Eclairage (CIE) coordinates of (0.13, 0.12) showed a maximum EQE of 23.4 % with a full-widthat-half-maximum of 18 nm and a LT 50 > 250 h at an L 0 of 1000 cd m À 2 .

Pure blue phosphorescent platinum(ii) emitters supported by NHC-based pincer type ligands with unitary emission quantum yields

“…43,44 Both phosphorescent and TADF-emitting materials can be used as sensitizers to convert the energy of both triplet and singlet excitons of the host to the singlet excitons of fluorescent dopants, giving PSF and TSF, respectively. 22,43–45,72–75 In the literature, the design of blue PSF OLEDs based on pure organic fluorescent dyes has mainly relied on blue iridium(III) cyclometalated phosphors as sensitizers in conjunction with blue florescent acceptors with lower triplet energies. 46,47 Apart from the exceptional PLQY, the [Pt(C NHC ^C Ar ^C NHC )L] complexes show emissions with high triplet energy ( E T ∼ 2.80 eV) that have good spectral overlap with the absorption spectrum of the blue florescent dye TBPe.…”

“…Multidentate cyclometalated NHC ligands concurrently possessing strong σ-donating strength and a large optical band gap have proved to be a privileged class of chromophoric ligands that effectively destabilize the 3 MC state relative to the emissive excited state of Pt( ii ) complexes for harvesting blue phosphorescence. 3,22–24 In a recent work, we reported a panel of dinuclear cyclometalated NHC Pt( ii ) emitters that attained high efficiency blue OLEDs with external quantum efficiencies (EQE) of 22.6% and diminished roll-off. 22 Herein is described a panel of blue pincer Pt( ii ) emitters [Pt(C NHC ^C Ar ^C NHC )L] supported by bis-imidazolylidene NHC pincer C NHC ^C Ar ^C NHC ligands and various anionic ancillary ligands L, including chloride, cyanide, isocyanoborate and pyrazolate, and their photophysical and electroluminescence characteristics (Scheme 1).…”

“…3,22–24 In a recent work, we reported a panel of dinuclear cyclometalated NHC Pt( ii ) emitters that attained high efficiency blue OLEDs with external quantum efficiencies (EQE) of 22.6% and diminished roll-off. 22 Herein is described a panel of blue pincer Pt( ii ) emitters [Pt(C NHC ^C Ar ^C NHC )L] supported by bis-imidazolylidene NHC pincer C NHC ^C Ar ^C NHC ligands and various anionic ancillary ligands L, including chloride, cyanide, isocyanoborate and pyrazolate, and their photophysical and electroluminescence characteristics (Scheme 1). Platinum( ii ) complexes with C NHC ^C Ar ^C NHC ligands were first reported by Li 25 and Hollis, Hammer and Webster 26 in 2012; the strong-field C NHC ^C Ar ^C NHC ligand serves as the luminophoric site with a wide optical band gap for achieving pure blue phosphorescence, and the ancillary ligand L modulates the nonradiative decay rate and propensity for intermolecular interactions.…”

Dinuclear Pt(II) Complexes with Red and NIR Emission Governed by Ligand Control of the Intramolecular Pt–Pt Distance

“…Phosphorescent Pt­(II) complexes have attracted great attention as phosphors in luminescence-based systems owing to their highly efficient emission properties. As a result, these complexes have been employed as phosphors for the organic light-emitting devices (OLEDs), − biological imaging probes, − and optical sensors. , However, Pt­(II) complexes often display additional long-wavelength emission resulting from the formation of excimers through ready stacking of their square planar molecular structures in concentrated solution or the solid-state. , The long wavelength emission mainly originates from metal–metal to ligand charge transfer (MMLCT), arising from metal–metal interactions through the overlap of d-orbitals that are oriented perpendicular to the square planes of the Pt­(II) complexes.…”

Carbazole-2-carbonitrile as an acceptor in deep-blue thermally activated delayed fluorescence emitters for narrowing charge-transfer emissions

“…7,20–22 Thus, at present, MREs are found to be useful as the terminal emitter (TE) in hyperfluorescence OLEDs. 23–25 Indeed, having stable blue D–A type TADF emitters with narrow emissions provides a more straightforward solution. However, the reports on blue narrow-emission (FWHM ≤ 50 nm) D–A type emitters are limited.…”