Phosphorescent Ir(III) complexes attract enormous attention because they allow highly efficient electrophosphorescence. In pursuing the development of Ir(III) complexes during the last decade, significant progress has been made in terms of the colour-tunability, thermal- and photo-stability, phase homogeneity, and phosphorescence efficiency. By far, extensive synthetic efforts have been focused on the molecular design of ligands to achieve a wide range of phosphorescence colour that is compatible with organic light-emitting device (OLED) applications. In contrast, less has been known about a collective structure–property relationship for phosphorescence quantum efficiency. In fact, a few rule-of-thumbs for high phosphorescence quantum efficiency have been occasionally reported, but a collective rationale is yet to be investigated. In this article, we provide a comprehensive review of 8 different methods reported so far to achieve high phosphorescence quantum efficiency from Ir(III) complexes. The methods included herein are limited to the cases of intramolecular controls, and thus are discussed in terms of variations in ligand structures: (1) geometric isomer control, (2) rigid structure and restricted intramolecular motion, (3) larger mixing of 1MLCT and 3LC states, (4) de-stabilizing a thermally accessible non-emissive state, (5) introducing dendrimer structures, (6) control in substituents of ligands, (7) confining the phosphorescent region of a mixed ligand Ir(III) complex and (8) sensitized phosphorescence by using attached energy donors. Each method is closely related to intramolecular excited state interactions, which strongly affect radiative or non-radiative transitions. A comprehensive understanding of these methods leads us to conclude that the modulation in ligand structures has a profound effect on both the phosphorescence colour and phosphorescence quantum efficiency. Thus, the judicious selection of ligand structures and their chelate disposition should be considered before synthesis. We expect that the guidelines for attaining a high phosphorescence efficiency, summarized in this Perspective, would be helpful in developing highly phosphorescent Ir(III) complexes.

Phosphorescent iridium(III) complexes: toward high phosphorescence quantum efficiency through ligand control

The development of cyclometalated Ir(III) complexes has enabled important breakthroughs in electroluminescence because such complexes permit the efficient population of triplet excited states that give rise to luminescent transitions. The triplet states of Ir(III) complexes are advantageous over those of other transition metal complexes in that their electronic transitions and charge-transfer characteristics are tunable over wide ranges. These favorable properties suggest that Ir(III) complexes have significant potential in a variety of photofunctions other than electroluminescence. In this critical review, we describe recent photonic applications of novel Ir(III) complexes. Ir(III) complexes have been shown to affect the exciton statistics in the active layers of organic photovoltaic cells, thereby improving the photon-to-current conversion efficiencies. Nonlinear optical applications that take advantage of the strong charge-transfer properties of triplet transitions are also discussed. The tunability of the electrochemical potentials facilitates the development of efficient photocatalysis in the context of water photolysis or organic syntheses. The photoredox reactivities of Ir(III) complexes have been employed in studies of charge migration along DNA chains. The photoinduced cytotoxicity of Ir(III) complexes on live cells suggests that the complexes may be useful in photodynamic therapy. Potential biological applications of the complexes include phosphorescence labeling and sensing. Intriguing platforms based on cyclometalated Ir(III) complexes potentially provide novel protein tagging and ratiometric detection. We envision that future research into the photofunctionality of Ir(III) complexes will provide important breakthroughs in a variety of photonic applications.

Photofunctional triplet excited states of cyclometalated Ir(III) complexes: beyond electroluminescence

Even though organic light-emitting device (OLED) technology has evolved to a point where it is now an important competitor to liquid crystal displays (LCDs), further scientific efforts devoted to the design, engineering and fabrication of OLEDs are required for complete commercialization of this technology. Along these lines, the present work reviews the essentials of OLED technology putting special focus on the general working principle of single and multilayer OLEDs, fluorescent and phosphorescent emitter materials as well as transfer processes in host materials doped with phosphorescent dyes. Moreover, as a prototypical example of phosphorescent emitter materials, a brief discussion of homo- and heteroleptic iridium(III) complexes is enclosed concentrating on their synthesis, photophysical properties and approaches for realizing iridium based phosphorescent polymers.

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Phosphorescent Organic Light-Emitting Devices: Working Principle and Iridium Based Emitter Materials

A Phosphorescent Ir(III) Complex for Selective Fluoride Ion Sensing with a High Signal‐to‐Noise Ratio

We disclose a controlled phosphorescence color tuning in a series of cyclometalated heteroleptic Ir(III) complexes (Ir(III) bis(2-(2,4-difluorophenyl)pyridinato-C,N2′)(LX)) containing chromophoric 2-(2-hydroxyphenyl)oxazole-derivative ancillary ligands (LX). From a cyclometalated chloride-bridged Ir(III) dimer, three highly emissive cyclometalated heteroleptic Ir(III) complexes were obtained in good yields, each with a different conjugative plane in the chromophoric ancillary ligand (i.e., 2-(2-hydroxyphenyl)-4-methyloxazole, 2-(2-hydroxyphenyl)-6-methylbenzoxazole, and 2-(2-hydroxyphenyl)naphthoxazole). The three Ir(III) complexes showed highly efficient greenish blue (500 nm), green (525 nm), and yellow (552 nm) phosphorescence, respectively; a regular ca. 0.11 eV bathochromic shift was observed for each additional phenyl ring fused to the oxazole ring in the ancillary ligand. From the absorption, electrochemical measurements, static and transient photoluminescence (PL), and time-dependent density funct...

Highly phosphorescent iridium complexes with chromophoric 2-(2-hydroxyphenyl)oxazole-based ancillary ligands: interligand energy-harvesting phosphorescence.

The synthesis, structure, and thermal, photophysical, and electroluminescent properties of bis(κ2(C2,N)-2-ppy)(κ2(N,O)-q)iridium(III) (ppy = phenylpyridine, q = 8-quinolinolate, 5-formyl-8-quinolinolate, or 5-nitro-8-quinolinolate) are described. The easily prepared compounds exhibit absorption and emission characteristics controlled by the quinolinolate ligand combined with increased thermal stability and enhanced OLED performance.

8-Quinolinolates as ligands for luminescent cyclometalated iridium complexes

An optical sensor for detecting an analyte of interest in a fluid medium (preferably gaseous medium), comprising an organic light emitting device (OLED) having at least two electrodes 2, 5 and an organic electroluminescent layer 4 that is sensible to an analyte contained in said fluid medium, said organic electroluminescent layer 4 being adapted to change its electroluminescence emission properties upon contact with said analyte for generating an optically detectable response. The optical sensor may be realised in a sandwich structure or may be in the form of a surface cell device. Changes in luminescence intensity, lifetime of the excited sates or emission wavelength may be monitored.

Optical sensor for detecting an analyte

TEM Characterization of Optoelectronic Devices Based on Conjugated Polymers: Can FIB Specimen Preparation Help?

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8-Quinolinolates as ligands for luminescent cyclometalated iridium complexes

Optical sensor for detecting an analyte

TEM Characterization of Optoelectronic Devices Based on Conjugated Polymers: Can FIB Specimen Preparation Help?