Fluorine-free blue-green emitters for light-emitting electrochemical cells

Abstract

New fluorine-free iridium complexes were synthesized in the aim of improving the performance of blue-green emitting LEECs.

Blue-green emitting cationic iridium complexes with 1,3,4-oxadiazole cyclometallating ligands: synthesis, photophysical and electrochemical properties, theoretical investigation and electroluminescent devices

“…1,5,19,20 However, high-energy emission is generally desired for many applications. [9][10][11] The former can be realized by including electron-withdrawing groups, such as F, to the phenyl ring of ppy, [21][22][23][24] or using non-conjugated NΛN ligands with strong ligand-field strength; 22, 25-28 the latter can be accomplished through attaching electron-donating groups to bpy, 29 or using electron-rich NΛN ligands, 30,31 such as 2-(1H-pyrazol-1-yl)pyridine (pzpy). [9][10][11] The former can be realized by including electron-withdrawing groups, such as F, to the phenyl ring of ppy, [21][22][23][24] or using non-conjugated NΛN ligands with strong ligand-field strength; 22, 25-28 the latter can be accomplished through attaching electron-donating groups to bpy, 29 or using electron-rich NΛN ligands, 30,31 such as 2-(1H-pyrazol-1-yl)pyridine (pzpy).…”

“…[9][10][11] The former can be realized by including electron-withdrawing groups, such as F, to the phenyl ring of ppy, [21][22][23][24] or using non-conjugated NΛN ligands with strong ligand-field strength; 22, 25-28 the latter can be accomplished through attaching electron-donating groups to bpy, 29 or using electron-rich NΛN ligands, 30,31 such as 2-(1H-pyrazol-1-yl)pyridine (pzpy). [33][34][35] Such an approach seems more appealing than the commonly used F substitution, 24 as C-F bonds are reactive and tend to rupture upon excitation of the complex. [33][34][35] Such an approach seems more appealing than the commonly used F substitution, 24 as C-F bonds are reactive and tend to rupture upon excitation of the complex.…”

Heteroleptic iridium (III) complexes with three different ligands: Unusual triplet emitters for light-emitting electrochemical cells

“…If at first sight, examination of such sophisticated complexes in devices can seem counter-intuitive, tris-heteroleptic complexes allow a high control of the emission wavelength without taking recourse to fluorination of the cyclometalated ligands. Indeed, since the pioneer works on iridium-based emitters, fluorination of the cyclometalated ligands has been extensively used and proved to be an effective tool to blue-shift the emission of complexes with a precision of 5e10 nm [50]. However, numerous works have recently evidenced the limitations of this strategy, defluorination of ligands occurring during complex synthesis [51e53] or during device operation [54,55].…”

Colour tuning by the ring roundabout: [Ir(C^N)2(N^N)]+ emitters with sulfonyl-substituted cyclometallating ligands

“…Another advantage of LECs over OLEDs is their far simpler architecture and the fact that they can be assembled using solution processing. 25 Following studies of blue emitting complexes for OLEDs, 26,27 Evariste et al 28 demonstrated the use of cyclometallated methyland methoxy-substituted 2,3 0 -bipyridine ligands as the C^N domain in blue-emitting [Ir(C^N) 2 (4,4 0 -t Bu 2 bpy)] + complexes. In [Ir(C^N) 2 (N^N)] + complexes, the HOMO contains contributions from the Ir(III) dp orbitals and phenyl p-orbitals of the cyclometallated C^N ligands, and the LUMO is usually localized on the N^N ligand.…”