Deep-Red Phosphorescent Iridium(III) Complexes Containing 1-(Benzo[b] Thiophen-2-yl) Isoquinoline Ligand: Synthesis, Photophysical and Electrochemical Properties and DFT Calculations

Abstract

Four new bis-cyclometalated iridium(III) complexes, [Ir(btq) 2phen] [PF6] (3a), [Ir(btq) 2bpy] [PF6] (3b), [Ir(btq) 2dtbipy] [PF6] (3c) and [Ir(btq) 2pic] (3d) (btq = 1-(benzo[b] thiophen-2-yl) isoquinoline, phen = 1,10-phenanthroline, bpy = 2,2'-bipyridine, dtbipy = 4,4'-di-tert-butyl-2,2'-bipyridine, pic = picolinic acid) have been synthesized and fully characterized. The crystal structure of 3a has been determined by X-ray analysis. The photophysical and electrochemical properties of these new complexes 3a - 3d have been studied. The photoluminescence spectra of all Ir(III) complexes exhibit deep-red emission maxima at 682, 682, 683 and 698 nm, respectively. The most representative molecular orbital energy-level diagrams and the lowest energy electronic transitions of 3a - 3d have been calculated with density functional theory (DFT) and time-dependent DFT (TD - DFT). The results show that the pic ancillary ligand of complex 3d influences the absorption and emission energies with a further red-shift relative to other three complexes 3a - 3c.

Ir(iii) complexes designed for light-emitting devices: beyond the luminescence color array

“…The use of 1-(benzo[b]- thiophen-2-yl)isoquinoline as a cyclometallated ligand in the [Ir(btq) 2 (L^X)] series, Table 1(vi), leads to red 3 MLCT Ir(btq)→L^X emission, with moderate quantum yields (ϕ ∼ 0.12). 75 The phenylbenzo[g]-quinoline ligand in [Ir( pbq-g) 2 (Ph 2 phen)] + , Table 1(vii), also results in a red emission, and a further redshift to the near infrared is observed after the addition of an electron-withdrawing sp 2 -N opposite to the chelating N atom in [Ir(mpbqx-g) 2 (Ph 2 phen)] + . 76,77 Another interesting strategy is the use of styryl-BODIPY ancillary ligands to harvest red and near infra-red light through π-conjugated linkers that ensure efficient intersystem crossing to long-lived emissive 3 LC BODIPY states.…”

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

“…This method has attracted much attention in the construction of NIR emitters owing to the relatively large redshift brought by thiophene and benzothiophene. 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 ).…”

Near‐IR Emitting Iridium(III) Complexes with Heteroaromatic β‐Diketonate Ancillary Ligands for Efficient Solution‐Processed OLEDs: Structure–Property Correlations

“…The UV/Vis/NIR absorption spectra of the three complexes in CH 2 Cl 2 at 298 K (Table and Figure a) show strong absorption bands in the region below λ =450 nm; this results from a complex spectroscopic admixture of π–π* and metal‐to‐ligand charge transfer (MLCT) transitions …”