Near-infrared emitting iridium complexes: Molecular design, photophysical properties, and related applications

Abstract

Summary Organic light-emitting diodes (OLEDs) have become popular displays from small screens of wearables to large screens of televisions. In those active-matrix OLED displays, phosphorescent iridium(III) complexes serve as the indispensable green and red emitters because of their high luminous efficiency, excellent color tunability, and high durability. However, in contrast to their brilliant success in the visible region, iridium complexes are still underperforming in the near-infrared (NIR) region, particular in poor luminous efficiency according to the energy gap law. In this review, we first recall the basic theory of phosphorescent iridium complexes and explore their full potential for NIR emission. Next, the recent advances in NIR-emitting iridium complexes are summarized by highlighting design strategies and the structure-properties relationship. Some important implications for controlling photophysical properties are revealed. Moreover, as promising applications, NIR-OLEDs and bio-imaging based on NIR Ir(III) complexes are also presented. Finally, challenges and opportunities for NIR-emitting iridium complexes are envisioned.

Deep-Red and Near-Infrared Iridium Complexes with Fine-Tuned Emission Colors by Adjusting Trifluoromethyl Substitution on Cyclometalated Ligands Combined with Matched Ancillary Ligands for Highly Efficient Phosphorescent Organic Light-Emitting Diodes

“…Furthermore, as its counterpart device with 10% concentration, m -BA10 showed similar high efficiencies of 14.0% and 12.3% based on 100 and 1000 nit, respectively. This EQE level is much higher the theoretical maximum values estimated from the PLQY of m -tFpqba as shown in Table 1 [ 23 ], indicating that the host and dopant molecules should have a molecular orientation type conducive to light extraction in both the emitting systems by adopting concentrations of 5 and 10 wt% [ 24 , 25 ], which is beneficial to improve the out-coupling efficiency and the resultant high EL efficiencies. In fact, the study on molecular arrangement and orientation in thin film is in progress in our group, but due to the limitations of experimental conditions, no desirable result has been achieved yet.…”

Azolate‐Based Osmium(II) Complexes with Luminescence Spanning Visible and Near Infrared Region

“…The respective red-emitting triazolate osmium(II) complexes (23 and 24) were also synthesized using an optimized two-stepin-one-pot process, which involved the in-situ preparation of the dicarbonyl intermediate from Os 3 (CO) 12 , followed by carbonyl-to-phosphine substitution that promoted by oxidative decarbonylation induced by Me 3 NO. [21] This modification gave desired osmium(II) complexes in much improved (> 70 %) yields and, hence, imposed a great advantage in scaling up for the possible industrial application.…”

“…There is only a limited number of single molecular dopants capable to achieve electroluminescence at such as long peak wavelength and with adequate efficiency at the same time. [12] Table 2 summarized the photoluminescence data of NIR emitting osmium(II) complexes mentioned in this section.…”

“…Due to the lowered formal oxidation state, the NIR emissive osmium(II) complexes are capable to exhibit more efficient NIR emission in comparison to their iridium(III) counterparts. [12]…”

Metal Peptide Conjugates in Cell and Tissue Imaging and Biosensing

“…N, N coordinating ligands that have σ-donating or п-accepting properties [ 24 – 27 ]. A recent review on NIR-emitting Ir(III) complexes discusses in detail the different methods that can be utilised to tune the photophysics of Ir(III) complexes [ 28 ]. Of note, although Ru(II) complexes are typically weaker emitters and less amenable to photophysical tuning than Ir(III) complexes, an advantage is that they tend to exhibit lower cytotoxicity upon uptake into cells [ 29 , 30 ].…”