Iridium Complexes Embedding Rigid D-A-Type Coordinated Cores: Facile Synthesis and High-Efficiency Near-Infrared Emission in Solution-Processed Polymer Light-Emitting Diodes

The Molecular Design and Electroluminescent Performance of Near-Infrared (NIR) Iridium(III) Complexes Bearing Isoquinoline-, Phthalazine- and Phenazine-Based Ligands

Near-infrared (NIR) light has characteristics of invisibility to human eyes, less background interference, low light scattering, and strong cell penetration. Therefore, NIR luminescent materials have significant applications in imaging, sensing, energy, information storage and display. The development of NIR luminescent materials thus has emerged as a highly dynamic area of research in the realm of contemporary materials. To date, NIR luminescent materials are roughly divided into inorganic materials and organic materials. Compared with inorganic materials, organic NIR luminescent materials have become a hot research topic in recent years due to their rich sources, easy control of structure, simple preparation process, low cost, and good film-forming properties. Among them, iridium(III) [Ir(III)] complexes exhibit excellent properties such as thermal stability, simple synthesis, easy color modulation, short excited state lifetimes, and high brightness, thus becoming one of the ideal luminescent material systems for preparing high-quality organic light-emitting diodes. Therefore, how to obtain Ir(III) complexes with NIR emission and high efficiency through molecular design is a necessary and promising research topic. This work reviews the research progress of representative NIR Ir(III) complexes bearing isoquinoline-, phenazine-, and phthalazine-based ligands reported in recent years and introduces the design strategies and electroluminescent performances of NIR Ir(III) complexes.

Azaacene containing iridium(III) phosphors: elaboration of the π-conjugation effect and application in highly efficient solution-processed near-infrared OLEDs

Azaacenes have attracted wide research interest due to their tremendous potential in organic electronics. However, near-infrared (NIR) light-emitting iridium(III) phosphors bearing azaacene derivatives are rarely investigated. In this contribution, two solution-processable heteroleptic iridium(III) complexes, namely DBPzIr and PPzIr, are rationally designed and synthesized, and they contain a rigid phenanthrene- or pyrene-fused diazaacene core and two peripheral groups of 4-tert-butyl-phenyl attached at the 12,13-positions in the core, respectively. The effects of the diazaacene core and appending groups on the optoelectronic properties of both complexes are systematically investigated. A dramatically red-shifted NIR emission peak at 789 nm with a photoluminescence quantum yield (PLQY) of 14% is observed in PPzIr compared with the 746 nm emission with a PLQY of 40% in DBPzIr. Taking advantage of their photophysical properties, the solution-processed device doped with DBPzIr achieves a maximum external quantum efficiency (EQEmax) of 8.00% with a radiance of 54 866 mW Sr-1 m-2 at 716 nm and the device doped with PPzIr exhibits a significantly red-shifted emission at 772 nm with an EQEmax of 3.53%. The achieved device performance is among the best values in the reported NIR-OLEDs based on iridium(III) complexes via a solution process at the same color gamut. Our study indicates that the reasonable collocation of the rigid diazaacene chelating core and flexible peripheral groups in the iridium(III) complex is of great significance in designing highly efficient NIR emitters.