High-efficiency and stable red to near-infrared organic light-emitting diodes using dinuclear platinum(ii) complexes

Abstract

Increasing the radiative decay rates of triplet excited states to overcome the energy-gap law is important for the development of high-efficiency and short-lived phosphorescent metal complexes in the red to...

Approaching the Shortest Intermetallic Distance of Half‐Lantern Diplatinum(II) Complexes for Efficient and Stable Deep‐Red Organic Light‐Emitting Diodes

“…As shown in Figure S4 (Supporting Information), quasireversible oxidations with half‐potentials ( E 1/2 ) of 0.44–0.61 V (vs Ag/AgCl) were observed for 1 – 6 , which are assigned to the oxidations of the PyXZ ligands and Pt atoms on the basis of density functional theory (DFT) calculations (vide infra). Comparing with the analogues using α ‐carboline bridges, [ 69 ] the stronger electron‐donating properties of PyXZ and shorter Pt–Pt distances lead to cathodic shifts of the oxidation potentials for 1 – 6 . The highest occupied molecular orbital (HOMO) levels of all the diplatinum(II) complexes are determined to be from −4.72 to −4.89 eV (Table 1).…”

“…Despite the deviation of exact Pt-Pt distance dependence of the radiative decay rates within 1-6, the radiative decays of the present diplatinum(II) complexes are slightly faster than those of previously reported analogues with longer Pt-Pt distances (> 2.90 Å). [55,69] It is necessary to point out that the formation of an oligomer (at least trimer) is usually essential for achieving deep red emissions from Pt(II) aggregates, thereby requiring subtle manipulation of the intermolecular packing diagram. [38] The confinement of short Pt-Pt distance using a rigid bridging ligand, as in 1-6 permits a more predictable design which does not rely on intermoelcular interactions.…”

“…The stability test for 3 using an unoptimized device structure unambiguously reveals the practicality of the present diplatinum(II) emitters, which have also been manifested on the other diplatinum(II) systems. [51,55,69]…”

Pyrazolate-Bridged NHC Cyclometalated [Pt2] Complexes and [Pt2Ag(PPh3)]+ Clusters in Electroluminescent Devices

“…To a lesser extent, dinuclear Pt­(II) complexes [Pt 2 ] have also been used in the fabrication of PhOLEDs. − In these cases, the bridging ligands also play an important role in controlling the Pt···Pt interaction and the nature of the excited states. Most of these complexes comprise two “Pt­(β-diketonate)” units bridged by a tetradentate ligand, which prevents intramolecular Pt···Pt interactions. ,− Among them, those in which the tetradentate ligand is doubly C ∧ N-cyclometalated are the most prevalent, ,− reaching external quantum efficiencies (EQEs) above 20%, only in a few cases. ,, Nevertheless, dinuclear complexes with a half-lantern (double decker) structure and short Pt···Pt distances have also been incorporated in PhOLEDs, obtaining EQE from 0.14 to 26.4% in the deep-red or NIR region. − Another family comprises complexes with pyrazolate bridging ligands of general formula [{Pt­(C ∧ E)­(μ-Rpz)} 2 ] (C ∧ E = 2-(4′,6′-difluorophenyl)­pyridinato-N,C 2’ ; Rpz = pyrazolate, 3-methyl-5- tert -butylpyrazolate, and 3,5-bis­( tert -butyl)­pyrazolate; C ∧ E = 2-(pyren-1-yl) pyridine, 2-(7-( tert -butyl)­pyren-1-yl)­pyridine, Rpz = 3,5-dimethylpyrazolate, and C ∧ E = Phenyl-NHC). In the former, the smaller the bulkiness of the pyrazolate, the greater the intramolecular Pt···Pt distance and the emission energy .…”