Boosting Efficiency of Near‐Infrared Organic Light‐Emitting Diodes with Os(II)‐Based Pyrazinyl Azolate Emitters

Abstract

Tremendous effort has been devoted to developing novel near-infrared (NIR) emitters and to improving the performance of NIR organic light-emitting diodes (OLEDs). Os(II) complexes are known to be an important class of NIR electroluminescent materials. However, the highest external quantum efficiency achieved so far for Os(II)-based NIR OLEDs with an emission peak wavelength exceeding 700 nm is still lower than 3%. A new series of Os(II) complexes (1-4) based on functional pyrazinyl azolate chelates and dimethyl(phenyl)phosphane ancillaries is presented. The reduced metal-to-ligand charge transfer (MLCT) transition energy gap of pyrazinyl units in the excited states results in efficient NIR emission for this class of metal complexes. Consequently, NIR OLEDs based on 1-4 show excellent device performance, among which complex 4 with a triazolate fragment gives superior performance with maximum external quantum efficiency of 11.5% at peak wavelength of 710 nm, which represent the best Os(II)-based NIR-emitting OLEDs with peak maxima exceeding 700 nm.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201906738. zation because of the strong spin-orbit coupling exerted by the thrid-row transition metal elements. [3,18,19] Among these, Pt(II)-based NIR OLEDs represent the state-of-the-art results in the range of 700-900 nm. [18,[20][21][22][23] In particular, in 2017, our group achieved a milestone in NIR OLEDs research, and realized NIR OLEDs with EQE up to 24 ± 1% at 740 nm by using the pyrazinyl pyrazolate Pt(II)-based emitter. [22] Although the efficiencies of these Pt(II)-based NIR OLEDs are remarkable, which also demonstrated a promising way to reduce the efficiency roll-off of the Pt(II)-based NIR OLEDs by using the metal-metal-to-ligand charge transfer (MMLCT) transition. [22][23][24] But in general, NIR OLEDs based on squareplanar Pt(II) emitters, particularly for porphyrin-based Pt(II) phosphors, typically suffer from serious efficiency roll-off at high current density, due to the long-lived triplet exciton generated and corresponding self-quenching. [18,21,25] In comparison Adv. Funct.

Phosphorescent Manganese(II) Complexes and Their Emerging Applications

“…In recent decades, phosphorescent transition-metal complexes (PTMCs) play a crucial role in the fields of advanced functional materials. [1][2][3][4][5][6][7][8] Quite different from the traditional fluorescent materials with the light emission from the singlet states, PTMCs are triplet emitters. [9][10][11][12][13][14] Since Forrest and coworkers successfully realized the first phosphorescent organic should be well noted that many phosphorescent manganese(II) complexes also exhibit ferroelectric properties.…”

“…In recent decades, phosphorescent transition‐metal complexes (PTMCs) play a crucial role in the fields of advanced functional materials. [ 1–8 ] Quite different from the traditional fluorescent materials with the light emission from the singlet states, PTMCs are triplet emitters. [ 9–14 ] Since Forrest and co‐workers successfully realized the first phosphorescent organic light‐emitting device (OLED) in 1998, [ 1 ] phosphorescent transition‐metal complexes, especially for noble metal‐based ones (e.g., iridium(III), platinum(II), etc.)…”

A simple and efficient approach toward deep-red to near-infrared-emitting iridium(iii) complexes for organic light-emitting diodes with external quantum efficiencies of over 10%

“…All the solvents were used directly without any treatment. 1 H, 13 C NMR and high resolution mass spectra (HRMS) were recorded on a Bruker AM400 spectrometer and Bruker Autoex (Fig. S8-S13 †).…”

“…1 To date, NIR OLEDs based on TADF organics, platinum(II) (Pt(II)) and osmium(II) (Os(II)) phosphors can achieve this goal. 5,[7][8][9][11][12][13] In general, the TADF emitter based NIR OLEDs exhibit very low luminance values to date. For example, by using an acenaphtho [1,2-b]pyrazine-8,9-dicarbonitrile (APDC) acceptor and two diphenylamine (DPA) donor units, Liao and co-workers synthesized NIR-emitting 3,4-bis(4-(diphenylamino)phenyl)ace-naphtho [1,2-b]pyrazine-8,9-dicarbonitrile (APDC-DTPA).…”

“…Remarkably, the efficiency roll-offs for these NIR OLEDs are nely restricted. 13 It seems that the Os(II) phosphors could be the best candidates for efficient and stable NIR OLEDs if the cost of the starting material dodecacarbonyltriosmium (Os 3 (CO) 12 ) is low. Therefore, these problems (such as low brightness values, serious efficiency roll-offs and high cost) will restrict the potential applications of these NIR-emitting materials and their electroluminescent (EL) devices.…”