Deep-Red/Near-Infrared to Blue-Green Phosphorescent Iridium(III) Complexes Featuring Three Differently Charged (0, −1, and −2) Ligands: Structures, Photophysics, and Organic Light-Emitting Diode Application

Abstract

We have designed and synthesized a new family of neutral phosphorescent iridium(III) complexes (Ir1−Ir6) featuring three differently charged (0, −1, and −2) ligands, in which biphenyl (bp) is used as a dianionic (−2) ligand, 4,6difluorophenylpyridine (dfppy) or 1-phenylisoquinoline (piq) is used as a monoanionic (−1) ligand, and 2,2′-bipyridyl (bpy), 1,10phenanthroline (phen), 1,2-bis(diphenylphosphanyl)benzene (dppb), or 1,2-bis(diphenylphosphanyl)ethane (dppe) is used as a neutral (0) ligand. The X-ray structures confirm that three coordination carbon atoms of all complexes assume a facial geometry, which can be beneficial to the stability of the structure. More importantly, the emitting color of the complexes can be tuned from deep red/near-infrared (NIR) (680−710 nm) to blue-green (466−496 nm) with different monoanionic (−1) ligands and neutral (0) ligands. Interestingly, the complex Ir5 shows a significant aggregation-induced phosphorescent emission effect, while Ir6 with a similar structure shows an opposite aggregation-caused quenching effect, mainly due to slight differences in the neutral (0) ligand structure. Notably, all deep red/NIR-emitting complexes (Ir1−Ir4) exhibit a distinct charge transfer (CT) excited state from the dianionic (−2) ligand to the neutral (0) ligand according to density functional theory calculations, whereas the excited state of blue-green-emitting complexes (Ir5−Ir6) displays the CT from the dianionic (−2) ligand to the monoanionic (−1) ligand. Considering better stability and optical performance, the deep red-emitting complexes (Ir2 and Ir4) with a simple structure are used as emitting layers of organic light-emitting diode devices and achieved good maximum external quantum efficiency (4.9 and 5.8%) peaking at 676 and 655 nm, respectively, with a very low turn-on voltage (2.5 V). This research provides a good strategy for the design of phosphorescent iridium complexes based on three differently charged (0, −1, and −2) ligands and their optoelectric applications.

A narrowband red-emitting asymmetric iridium(iii) complex featuring B- and N-embedded π-conjugation units: structure, photophysics and OLED application

“…Importantly, it also shows good maximum external quantum efficiency (EQE) (4.9%), which is comparable to the results of evaporation type OLED devices containing asymmetric iridium complexes reported previously. 7,35 In addition, the device exhibits a relatively low turn-on voltage (3.9 V), which is mainly due to the good energy level match between the layers of the device and the ambipolar characteristics of the iridium complex IrBNacac, and is beneficial for carrier transport.…”

“…Phosphorescent metal iridium(III) complexes, as excellent room temperature phosphorescent materials, are widely used in organic light-emitting diodes (OLEDs), [1][2][3][4][5][6][7][8][9][10] chemical sensing, [11][12][13][14][15] biological imaging, [16][17][18][19][20] photocatalysts for organic reactions, [21][22][23][24] etc. Especially for phosphorescent OLEDs which can be used in flat-panel displays and lighting sources, metal iridium complexes have more advantages, including a stable octahedral coordination structure, a suitable luminescence lifetime, an adjustable luminescence color, high luminescence efficiency and exciton utilization.…”

Geometric isomers of asymmetric rigid four-membered chelating ring based deep-red-emitting iridium complexes featuring three charged (0, −1, −2) ligands

“…First, the iridium complex precursors (2a and 2b) can be obtained from biphenylene and the iridium(I) complex [Ir (COD)Cl] 2 using the previously reported two-step method. 23,24 Then the reaction of the iridium complex precursors (2a and 2b) with an equal amount of the four-membered ring S^N ligand at a low temperature (90 °C) produces the kinetic isomers Ir1K and Ir2K, while a higher temperature (130 °C) leads to the formation of their corresponding thermodynamic isomers (Ir1T and Ir2T). (Fig.…”

“…[15][16][17] However, most of the geometric isomers reported to date exist in iridium complexes with three monoanionic (−1, −1, −1) ligands, [15][16][17][18][19][20][21][22] while none have been reported in three charged (0, −1, −2) ligand based iridium complexes (Fig. 1a), [23][24][25][26][27] which have been developed in recent years and tend to emit red or nearinfrared light more easily. Therefore, it is of great significance to study the synthesis, structures and optical properties of geometric isomers in such new three-charged (0, −1, −2) ligand systems.…”

Iridium(III) Complex Radical and Corresponding Ligand Radical Functionalized by a Tris(2,4,6-trichlorophenyl)methyl Unit: Synthesis, Structure, and Photophysical Properties

“…Based on this, it is worth looking forward to introducing the TTM unit into other luminescent metal complexes and studying how the TTM luminescence moiety interacts with the metal luminescence center. On the other hand, phosphorescent metal iridium­(III) complexes, − as a class of classical luminescent materials with excellent properties, are widely used in various photo-functional fields, such as organic light-emitting diodes, biological imaging, and chemical sensing. In particular, it is worth emphasizing that these iridium complexes can produce room temperature phosphorescence in the form of a triplet state.…”