Unravelling the Mechanism of Excited-State Interligand Energy Transfer and the Engineering of Dual Emission in [Ir(C∧N)2(N∧N)]+ Complexes

Scattergood, Paul A.; Ranieri, Anna Maria; Charalambou, Luke; Comia, Adrian; Ross, Daniel A. W.; Rice, Craig R.; Hardman, Samantha J. O.; Heully, Jean‐Louis; Dixon, Isabelle M.; Massi, Massimiliano; Alary, Fabienne; Elliott, Paul I. P.

doi:10.1021/acs.inorgchem.9b03003

Cited by 43 publications

(49 citation statements)

References 73 publications

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“…Fc/Fc + , all of which are assigned to reduction of the N^N donor fragment. The redox potentials reported herein are in line with those for similar rhenium-triazole complexes investigated by Ching et al and with data from our laboratory for osmium(II) and iridium(III) complexes bearing pyridylversus pyrazinyltriazole ligands [36,37]. In agreement with the stabilisation of the pyrimidine-and pyrazine-localised LUMOs for 2 and 3, respectively, relative to that of 1, the electrochemical reduction features of 2 and 3 are anodically shifted with respect to the corresponding pyridyltriazole complex (1).…”

Section: Cyclic Voltammetrysupporting

confidence: 92%

“…The emission spectra follow the same trend for the electronic absorption spectra with red-shifting of the 3 MLCT bands in the order 1 (540 nm) < 2 (572 nm) < 3 (638 nm). This again reflects the progressive stabilisation of the pyrimidine and pyrazine centred LUMO in these complexes relative to that of 1 and mirrors the trend in 3 MLCT/ 3 LL'CT state energies observed in iridium(III) complexes containing these ligands [36]. Emission spectra at 77 K revealed similar featureless 3 MLCT-derived emission bands, which follow the same trend in energy as exhibited at room temperature (λ em 1 < 2 < 3), although with all emission maxima now shifted to higher energy owing to rigidochromic effects.…”

Section: Electronic Structuresupporting

confidence: 70%

“…The ligands 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (pymtz) and 1-benzyl-4-(pyrazine-2-yl)-1,2,3-triazole (pyztz) were prepared as previously reported [36]. The complexes [Re(NˆN)(CO) 3 Cl] (NˆN = pymtz (2); pyztz (3)) were prepared through heating to reflux the ligands in the presence of [Re(CO) 5 Cl] in toluene and were isolated in good to moderate yields.…”

Section: Ligand Synthesis and Characterizationmentioning

confidence: 99%

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Photophysical and Electrocatalytic Properties of Rhenium(I) Triazole-Based Complexes

et al. 2020

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A series of [Re(N^N)(CO)3(Cl)] (N^N = diimine) complexes based on 4-(pyrid-2-yl)-1,2,3-triazole (1), 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (2), and 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (3) diimine ligands were prepared and their photophysical and electrochemical properties were characterized. The ligand-based reduction wave is shown to be highly sensitive to the nature of the triazole-based ligand, with the peak potential shifting by up to 600 mV toward more positive potential from 1 to 3. All three complexes are phosphorescent in solution at room temperature with λmax ranging from 540 nm (1) to 638 nm (3). Interestingly, the complexes appear to show inverted energy-gap law behaviour (τ = 43 ns for 1 versus 92 ns for 3), which is tentatively interpreted as reduced thermal accessibility of metal-centred (3MC) states from photoexcited metal to ligand charge transfer (3MLCT) states upon stabilisation of the N^N-centred lowest unoccupied molecular orbital (LUMO). The photophysical characterisation, supported by computational data, demonstrated a progressive stabilization of the LUMO from complex 1 to 3, which results in a narrowing of the HOMO–LUMO energy gap (HOMO = highest occupied molecular orbital) across the series and, correspondingly, red-shifted electronic absorption and photoluminescence spectra. The two complexes bearing pyridyl (1) and pyrimidyl (2) moieties, respectively, showed a modest ability to catalyse the electroreduction of CO2, with a peak potential at ca. −2.3 V versus Fc/Fc+. The catalytic wave that is observed in the cyclic voltammograms is slightly enhanced by the addition of water as a proton source.

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Section: Cyclic Voltammetrysupporting

confidence: 92%

Section: Electronic Structuresupporting

confidence: 70%

Section: Ligand Synthesis and Characterizationmentioning

confidence: 99%

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Photophysical and Electrocatalytic Properties of Rhenium(I) Triazole-Based Complexes

et al. 2020

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“…Of course, previous studies have investigated a variety of different aryl groups as components of cyclometallating C^N ligands, including early, seminal [21] studies on luminescent Ir III complexes [26] . Other recent examples of red phosphorescence from Ir III species have been achieved through the use of conjugated triazole, [27] conjugated phenazine, [28] and cyclometallating phenylquinazoline [29] ligands. Teets and co‐workers have also described a systematic study of a series of anionic ancillary ligands which facilitate excellent control over the emitting state energies of their Ir III complexes [30] .…”

Section: Introductionmentioning

confidence: 99%

Iridium(III) Sensitisers and Energy Upconversion: The Influence of Ligand Structure upon TTA‐UC Performance

Elgar

Otaif

Zhang

et al. 2021

Chemistry A European J

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Six substituted ligands based upon 2‐(naphthalen‐1‐yl)quinoline‐4‐carboxylate and 2‐(naphthalen‐2‐yl)quinoline‐4‐carboxylate have been synthesised in two steps from a range of commercially available isatin derivatives. These species are shown to be effective cyclometallating ligands for IrIII, yielding complexes of the form [Ir(C^N)2(bipy)]PF6 (where C^N=cyclometallating ligand; bipy=2,2′‐bipyridine). X‐ray crystallographic studies on three examples demonstrate that the complexes adopt a distorted octahedral geometry wherein a cis‐C,C and trans‐N,N coordination mode is observed. Intraligand torsional distortions are evident in all cases. The IrIII complexes display photoluminescence in the red part of the visible region (668–693 nm), which is modestly tuneable through the ligand structure. The triplet lifetimes of the complexes are clearly influenced by the precise structure of the ligand in each case. Supporting computational (DFT) studies suggest that the differences in observed triplet lifetime are likely due to differing admixtures of ligand‐centred versus MLCT character instilled by the facets of the ligand structure. Triplet–triplet annihilation upconversion (TTA‐UC) measurements demonstrate that the complexes based upon the 1‐naphthyl derived ligands are viable photosensitisers with upconversion quantum efficiencies of 1.6–6.7 %.

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“…[12] Thus, the final emissive state can be affected by ILET from the higher energy state to the lower energy state without distinction between the main or ancillary ligands. ILET dynamics typically occur at an ultrafast time scale (10 À 12 -10 À 10 s) and have been directly investigated using emission up-conversion [13] and femtosecond transient absorption (fs-TA) [8,12,[14][15][16][17][18] techniques.…”

Section: Introductionmentioning

confidence: 99%

Inter‐Ligand Energy Transfer Process in an Ir‐Complex with Expanding π‐Conjugated Ligand

et al. 2020

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The inter-ligand energy transfer (ILET) process in heteroleptic iridium complex, [Ir(dfppy) 2 (bpy-Im 2)] + , where dfppy = 2-(2,4difluorophenyl)pyridine and bpy-Im 2 = 4,4'-bis(1,2-diphenyl-1Hbenzo[d]imidazole)-2,2',-bipyridine, was investigated using a femtosecond transient absorption (fs-TA) spectroscopic technique. The photophysical properties of [Ir(dfppy) 2 (bpy-Im 2)] + with significantly expanding π-conjugated ligand are compared to those of [Ir(dfppy) 2 (bpy)] + (bpy = 2,2'-bipyridine) and a free bpy-Im 2 ligand. The emission spectrum of [Ir(dfppy) 2 (bpy-Im 2)] + shows no shift upon changing the solvent polarity, whereas the free ligand bpy-Im 2 showed bathochromic fluorescence shifts with increasing solvent polarity, which is attributed to intramolecular charge transfer (ICT). The unique photophysical properties of [Ir(dfppy) 2 (bpy-Im 2)] + are due to the fast ILET process from 3 MLCT dfppy to 3 MLCT/ 3 LC bpy-Im2 , resulting in the phosphorescence emission originating from 3 MLCT/ 3 LC bpy-Im2. On the other hand, the TA bands of bpy-Im 2 are observed at 540 and 480 nm, corresponding to the singlet and triplet manifolds, respectively. In contrast, the TA spectrum of [Ir(dfppy) 2 (bpy-Im 2)] + showes broad bands centered at 420 and 600 nm, attributed to the transitions from 3 MLCT dfppy and 3 MLCT/ 3 LC bpy-Im2 , respectively. Time-resolved spectroscopic results confirm the efficient ILET dynamics from 3 MLCT dfppy to 3 MLCT/ 3 LC bpy-Im2 in [Ir(dfppy) 2 (bpy-Im 2)] +. From the relaxation times determined by singular value decomposition analysis and simple sequential kinetic model, we infer that the ILET process from 3 MLCT dfppy to 3 MLCT/ 3 LC bpy-Im2 occurs with a time constant of ca. 4 ps. The presented results in this study show that the introduction of an expanding π-conjugated ligand can lead to the efficient ILET dynamics for improving the OLED performance.

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Unravelling the Mechanism of Excited-State Interligand Energy Transfer and the Engineering of Dual Emission in [Ir(C^∧N)₂(N^∧N)]⁺ Complexes

Cited by 43 publications

References 73 publications

Photophysical and Electrocatalytic Properties of Rhenium(I) Triazole-Based Complexes

Photophysical and Electrocatalytic Properties of Rhenium(I) Triazole-Based Complexes

Iridium(III) Sensitisers and Energy Upconversion: The Influence of Ligand Structure upon TTA‐UC Performance

Inter‐Ligand Energy Transfer Process in an Ir‐Complex with Expanding π‐Conjugated Ligand

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