Divalent Osmium Complexes:  Synthesis, Characterization, Strong Red Phosphorescence, and Electrophosphorescence

Abstract

We report new divalent osmium complexes that feature strong red metal-to-ligand-charge-transfer (MLCT) phosphorescence and electrophosphorescence. The general formula of the complexes is Os(II)(N-N)(2)L-L, where N-N is either a bipyridine or a phenanthroline and L-L is either a phosphine or an arsine. New polypyridyl ligands synthesized are 4,4'-di(biphenyl)-2,2'-bipyridine (15) and 4,4'-di(diphenyl ether)-2,2'-bipyridine (16), and the 1,10-phenanthroline derivatives synthesized are 4,7-bis(p-methoxyphenyl)-1,10-phenanthroline (17), 4,7-bis(p-bromophenyl)-1,10-phenanthroline (18), 4,7-bis(4'-phenoxybiphen-4-yl)-1,10-phenanthroline (19), and 4,7-bis(4-naphth-2-ylphenyl)-1,10-phenanthroline (20). 4,4'-Diphenyl-2,2'-bipyridine (21) and 4,7-diphenyl-1,10-phenanthroline (22) were also used in these studies. Strong pi-acid ligands used were 1,2-bis(diphenylarseno)ethane (23), cis-1,2-bis(diphenylphosphino)ethylene (24), and cis-1,2-vinylenebis(diphenylarsine) (25). Ligand 25 is used for the first time in these types of luminescent osmium complexes. These compounds feature strong MLCT absorption bands in the visible region and strong red phosphorescent emission ranging from 611 to 651 nm, with quantum efficiency up to 45% in ethanol solution at room temperature. Red organic light-emitting diodes (OLEDs) were successfully fabricated by doping the Os(II) complexes into blend of poly(N-vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD). Brightness over 1400 cd/m(2) for a double-layer device has been reached, with a turn-on voltage of 8 V. The maximum external quantum efficiency was 0.64%. Commission Internationale de l'Eclairage (CIE) chromaticity coordinates (x, y) of the red electrophosphorescence from the complexes are (0.65, 0.34), which indicates pure red emission.

Tailoring Optoelectronic Properties of Phenanthroline‐Based Thermally Activated Delayed Fluorescence Emitters through Isomer Engineering

“…[6,7,14,20,24] Although promising results have been achieved on TADF emitters with the state-of-art external quantum efficiencies (η ext s) close to those of phosphorescent OLEDs, the further improvement in the device efficiency and stability is still in demand, and the insight into the relationship between the TADF molecular structures and properties is to be deepened. [10,[24][25][26][27][28] Phenanthroline derivatives have been widely used as efficient electron-transporting materials, [29,30] good host materials, [31,32] and ligand of phosphorescent emitters [33][34][35][36][37][38] in OLEDs, in virtue of their efficient electron transporting properties, good thermal stability, rigid planar structure, and easy structure modification. In this article, we designed and synthesized three isomeric phenanthroline derivatives (as shown in Scheme 1, collectively named x-PXZP, x = o, m, p), i.e., 2,9-di(10H-phenoxazin-10-yl)-1,10-phenanthroline (o-PXZP), 3,8-di(10H-phenoxazin-10-yl)-1,10-phenanthroline (m-PXZP), and 4,7-di(10H-phenoxazin-10-yl)-1,10-phenanthroline (p-PXZP), with phenoxazine (PXZ) unit linked to the ortho-, meta-and para-position of nitrogen atoms in highly rigid phenanthroline core, in which PXZ unit is widely used electron donor in TADF emitters for its strong electron-donating ability and suitable steric hindrance.…”

A Modular Approach to Luminescent Dinuclear Ruthenium(II) and Rhenium(I) Complexes

“…[3] Initially concentrated on the ubiquitous [Ru(bpy) 3 ] 2+ motif, [4,5] the family of photoactive transition metals has extended to include the analogous osmium complexes, [6][7][8][9] the acetylene complexes of platinum [10] and the cyclometallated benzopyridine complexes of iridium(III). [11] Interest in (bipyridyl)tricarbonylrhenium(I) complexes has given rise to a wealth of new luminescent materials [12] with potential application in metal-mediated photo-induced reduction of carbon dioxide [13][14][15] and sensing devices.…”

Synthesis and Characterization of Dibenzo[a,d]cyclohepten‐5‐one Derivatives for Light‐Emitting Diodes

“…[1][2][3][4] Luminescent materials are the most crucial factors affecting electroluminescent (EL) properties of the OLED devices. [5][6][7][8][9][10] In most applications, emissive materials with excellent all-round properties are required for OLED devices. To achieve high-performance OLED devices, the organic luminescent materials usually need to meet some requirements, such as good thermal stabilities, excellent film-forming properties, good carrier injection/transport abilities, appropriate energy levels, and outstanding photoluminescent (PL) characteristics, etc.…”