“…In some cases, the alkoxy groups are more detrimental to the PLQY than the alkyl groups, probably because the nπ∗ state brought by the oxygen atom would quench the emissive excited state, as in complex 44 ( You et al., 2020b ). Similar side effect appeared in complexes with ethoxy acyl group, as in complexes 24 and 41 ( Kim et al., 2018a , 2020a , 2020b ). Figure 7 Representative NIR-emitting Ir(III) complexes with flexible chains linked directly on the core of ligands …”
Section: Molecular Designs For Nir-emitting Ir(iii) Complexessupporting
confidence: 69%
“…In this situation, the Huang-Rhys parameter could be estimated from the relationship , in which is the intensity at the electronic origin (0–0 transition) and is the total emission intensity ( Lai and Teets, 2019 ). The estimated Huang-Rhys parameters may help with molecular optimization and discussion of photophysical properties for a parallel series of molecules and have been employed in some reports of NIR-emitting Ir(III) complexes ( Kim et al., 2018a ; Lai et al., 2020 ; You et al., 2020a ).…”
Section: Basic Knowledge and Theoretical Backgroundmentioning
confidence: 99%
“…The 1-benzo[ b ]thien-2-yl-isoquinoline (btiq) is easy to synthesize and has been a frequently used cyclometalated ligand in NIR Ir(III) emitters, such as complexes 6 ( Ikawa et al., 2013 ), 7 ( Li et al., 2014 ), 14, 15, 16 ( Kesarkar et al., 2016 ), 23 ( Fu et al., 2018 ), 27 ( Guo et al., 2019 ), and 29 ( Zhou et al., 2019a ).The resulting complexes are just enough to give emissions around 700 nm with moderate PLQYs. Similarly, 2-benzo[ b ]thien-2-yl-quinoline (btq), the isomer of btiq, was also reported to develop NIR-emitting complexes, in which some electron-deficient substitutions were employed to realize NIR emission, as in complexes 24, 25 ( Kim et al., 2018a ), 41, and 42 ( Kim et al., 2020a ). Figure 6 Representative Ir(III) complexes with C part modifications based on thiophene rings Their PL emission wavelengths in dilute solutions are also provided.…”
Section: Molecular Designs For Nir-emitting Ir(iii) Complexesmentioning
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.
“…In some cases, the alkoxy groups are more detrimental to the PLQY than the alkyl groups, probably because the nπ∗ state brought by the oxygen atom would quench the emissive excited state, as in complex 44 ( You et al., 2020b ). Similar side effect appeared in complexes with ethoxy acyl group, as in complexes 24 and 41 ( Kim et al., 2018a , 2020a , 2020b ). Figure 7 Representative NIR-emitting Ir(III) complexes with flexible chains linked directly on the core of ligands …”
Section: Molecular Designs For Nir-emitting Ir(iii) Complexessupporting
confidence: 69%
“…In this situation, the Huang-Rhys parameter could be estimated from the relationship , in which is the intensity at the electronic origin (0–0 transition) and is the total emission intensity ( Lai and Teets, 2019 ). The estimated Huang-Rhys parameters may help with molecular optimization and discussion of photophysical properties for a parallel series of molecules and have been employed in some reports of NIR-emitting Ir(III) complexes ( Kim et al., 2018a ; Lai et al., 2020 ; You et al., 2020a ).…”
Section: Basic Knowledge and Theoretical Backgroundmentioning
confidence: 99%
“…The 1-benzo[ b ]thien-2-yl-isoquinoline (btiq) is easy to synthesize and has been a frequently used cyclometalated ligand in NIR Ir(III) emitters, such as complexes 6 ( Ikawa et al., 2013 ), 7 ( Li et al., 2014 ), 14, 15, 16 ( Kesarkar et al., 2016 ), 23 ( Fu et al., 2018 ), 27 ( Guo et al., 2019 ), and 29 ( Zhou et al., 2019a ).The resulting complexes are just enough to give emissions around 700 nm with moderate PLQYs. Similarly, 2-benzo[ b ]thien-2-yl-quinoline (btq), the isomer of btiq, was also reported to develop NIR-emitting complexes, in which some electron-deficient substitutions were employed to realize NIR emission, as in complexes 24, 25 ( Kim et al., 2018a ), 41, and 42 ( Kim et al., 2020a ). Figure 6 Representative Ir(III) complexes with C part modifications based on thiophene rings Their PL emission wavelengths in dilute solutions are also provided.…”
Section: Molecular Designs For Nir-emitting Ir(iii) Complexesmentioning
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.
“…It is known that frontier molecular orbitals (FMO) of complex ground state S 0 are related to its spectral properties [86]. Emission color of iridium(III) complexes can be adjusted by changing their HOMO-LUMO bandgap, which can be achieved on the course of ligand functionalization with electron-donating and electronwithdrawing substituents [86], and values of HOMO-LUMO gaps predicted for Ir(III) complexes by DFT methods showed surprisingly good correlation with the experimentally recorded values of energies of emitted photons even in the case of phosphorescence, see for example [21,22,[83][84][85][87][88][89][90]. Contour plots of frontier orbitals of both [Ir(bzq) 3 ] isomers are depicted in Fig.…”
A series of facial fac-[Ir(5-R-bzq) 3 ] and meridional mer-[Ir(5-R-bzq) 3 ] Ir(III) complexes bearing benzo[h]quinoline-based ligands have been studied with the help of density functional theory (DFT) methods. A detailed electronic structure comparison of the two isomers has been addressed to point out the differences in their stability and photophysical properties. An influence of substituent impact on optical and electronic properties of Ir(III) homoleptic complexes was also explored by introducing into the cyclometalated ligands substituents characterized with different electronic properties, e.g., R = H, F, OPh, NMe 2 , C 6 F 5 , and p-C 6 H 4-NPh 2. The results herein show that fac and mer isomers exhibit remarkable differences in stability and photophysical properties. The introduction of different functional groups into bzq ligands, despite very similar geometrical structures, significantly affected HOMO and LUMO energy levels and energy gaps of the examined Ir(III) complexes.
“…In general, the commonly used NIR emitting materials consist of inorganics (such as nanocrystals ( Mao et al., 2014 ) and quantum dots ( Pichaandi and Van Veggel, 2014 )) and organic molecules (including organic fluorophores ( Qian and Wang, 2010 ), transition-metal-based phosphors ( Xiang et al., 2013 ), and so on). To achieve efficient organic NIR emitters, thermally activated delayed fluorescence (TADF) organics ( Kim et al., 2018a ) and organometallic phosphors based on Pt(II) ( Ly et al., 2017 ), Os(II) ( Liao et al., 2015 ), and Ir(III) complexes ( Kim et al, 2018b ) which can harness the energy of both 25% singlet and 75% triplet excited states are the most studied materials for getting high EQEs. Meanwhile, the luminescent radicals whose emissions originate from a spin doublet ( Peng et al., 2015 ) are also considered to be one candidate material because the neutral radicals are capable of circumventing the efficiency limitations imposed by the triplet excitons.…”
Summary
Achieving the high external quantum efficiency (EQE) of near-infrared (NIR) emission in iridium(III) complexes still remains a challenge owing to their unsteady excited states which easily decay to the ground states through the nonradiative pathways. Herein, three Ir(III) phosphors in which the cyclometalated ligand 1-phenylisoquinoline-4-carbonitrile (piq-CN) is functionalized with the cyano,
tert-
butyl, and dimethyl groups are developed (CN-CNIr, Bu-CNIr, and DM-CNIr, respectively). Three simple synthetic steps can afford this class of deep red to NIR Ir(III) emitters. The organic light-emitting diodes (OLEDs) based on Bu-CNIr and DM-CNIr attain the maximum EQEs of 7.1% and 7.2% with the emission peaks at 695 and 714 nm, respectively. This strategy using substituted piq-CN derivatives as the cyclometalated ligands can offer an effective approach to promote the radiative rate of NIR-emitting Ir(III) materials. An insight into how the electron-withdrawing and electron-donating substituents on ligands influence the optoelectronic properties of their Ir(III) complexes is also provided.
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