Near infrared-emitting tris-bidentate Os(<scp>ii</scp>) phosphors: control of excited state characteristics and fabrication of OLEDs

Liao, Jia-Ling; Chi, Yun; Yeh, Chih-Ting; Kao, Hao-Che; Chang, Chih-Hao; Fox, Mark A.; Low, Paul J.; Lee, Gene‐Hsiang

doi:10.1039/c5tc00204d

Cited by 52 publications

(34 citation statements)

References 84 publications

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“…Based upon our previous work, together with that of others, we initially expected the potential of this oxidation process, though perturbed, to be but relatively insensitive to the changing nature of the ligands across the series owing to the HOMO being predominantly osmium d-orbital in character. 7,12,35,56,57 However, the electrochemical data reveal this couple to also be significantly affected by the incorporation of pyrazine units On examining the literature we note that these results on pyrazine ligand-based stabilisation of the HOMO Whilst we were not able to synthetically isolate the terpyrazine (tpz) complex [Os(tpz)2] 2+ (Os7) we might predict that it would possess absorption and emission spectra further blue-shifted compared to those of Os6 based on experimental data for bpz complexes compared to their bpy analogues. [58][59][60] We therefore also optimised the ground state of the complex Os7 in our DFT calculations in order to determine whether the further inclusion of pyrazine donors into the ligand set would lead to further inverted optoelectronic tuning.…”

Section: Complexmentioning

confidence: 99%

Observation of an Inversion in Photophysical Tuning in a Systematic Study of Luminescent Triazole-Based Osmium(II) Complexes

et al. 2019

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In a systematic survey of luminescent bis(terdentate) osmium(II) complexes a tipping-point involving reversal in photophysical tuning is observed whereby increasing stabilisation of the ligand-based LUMO results in a blue-shift in optical absorption and emission bands. The complexes [Os(N^N'^N")2] 2+ (N^N'^N" = 2,6-bis(1-phenyl-1,2,3-triazol-4-yl)pyridine (Os1); 2,6-bis(1-benzyl-1,2,3-triazol-4-yl)pyrazine (Os2); 6-(1-benzyl-1,2,3-triazol-4-yl)-2,2'-bipyridyl (Os3); 2-(pyrid-2-yl)-6-(1-benzyl-1,2,3-triazol-4-yl)pyrazine (Os4); 2-(pyrazin-2-yl)-6-(1-benzyl-1,2,3-triazol-4-yl)pyridine (Os5); 6-(1-benzyl-1,2,3-triazol-4-yl)-2,2'bipyrazinyl (Os6)) have been prepared and characterised and all complexes display phosphorescence ranging from the orange to near-IR regions of the spectrum. Replacement of the central pyridine in the ligands of Os1 by the more -accepting pyrazine in Os2 results in a 55 nm red-shift in the 3 MLCT-based emission band whilst a larger red-shift of 107 nm is observed for replacement of one of the triazole donors in the ligands of Os1 by a second pyridine ring in Os3 ( em max = 702 nm). Interestingly, replacement of the central pyridine ring in the ligands of Os3 by pyrazine Os4 ( em max = 702 nm) fails to result in a further red-shift in the emission band. Reversal of the relative positions of the pyridine and pyrazine donors in Os5 ( em max = 733 nm) compared to Os4 does indeed result in the expected red-shift in emission with respect to that for Os3 based on the increased -acceptor character of the ligands present. However, an inversion in emission tuning is observed for Os6 in which the incorporation of a second pyrazine donor in the ligand architecture results in a blue-shift in optical absorption and emission maxima ( em max = 710 nm). Electrochemical studies reveal that whilst incorporating pyrazine into the ligands indeed results in an expected anodic shift in the first reduction potential through stabilisation of the ligand-based LUMO, there is also concomitant anodic shift in the Os(II)/Os(III)-based oxidation potential. This stabilisation of the metal-based HOMO thus nullifies the effect of the stabilisation of the LUMO in Os4 compared to Os3 resulting in these complexes having coincident emission maxima. For Os6 the stabilisation of the HOMO through incorporation of two pyrazine donors in the ligand structure now exceeds the stabilisation of the LUMO resulting in a larger HOMO-LUMO gap and the counter-intuitive blue-shift in optical properties in comparison with Os5. Whilst it is known that replacement of ligands (e.g. replacing bipyridyl with bipyrazinyl) can result in a larger HOMO-LUMO energy gap through greater stabilisation of the HOMO, these results importantly allow us to capture the tipping-point at which this inversion in photophysical tuning occurs. This therefore enables us to explore the limits available in emission tuning with a relatively simple and minimalist ligand structure. 13 , including functioning as the low-energy aspect within multi-component white light sy...

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Section: Complexmentioning

confidence: 99%

Observation of an Inversion in Photophysical Tuning in a Systematic Study of Luminescent Triazole-Based Osmium(II) Complexes

et al. 2019

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“…However, for a long time, the efficiencies of NIR OLEDs are much lower than those of visible light‐emitting OLEDs because of the rarity of highly efficient NIR emitters. Although pure organic molecules, conjugated polymers or organometallic complexes based on osmium(II), iridium(III), lanthanide, and platinum(II) have been used as NIR emitters. Most of NIR emitters are designed by extending the conjugated system and/or adopting donor‐acceptor structure, which increases the complexity of synthetic process, and thereby leads to the rarity of NIR emitters.…”

Section: Methodsmentioning

confidence: 99%

Enhancing Molecular Aggregations by Intermolecular Hydrogen Bonds to Develop Phosphorescent Emitters for High‐Performance Near‐Infrared OLEDs

Yang

Guo

et al. 2019

Advanced Science

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Phosphorescent near‐infrared (NIR) organic light‐emitting devices (OLEDs) have drawn increasing attention for their promising applications in the fields such as photodynamic therapy and night‐vision readable displays. Here, three simple phosphorescent Pt(II) complexes are synthesized, and their intermolecular interactions are investigated in crystals and neat films by X‐ray single crystal diffraction and grazing‐incidence wide‐angle X‐ray scattering, respectively. The photophysical properties, molecular aggregation (including Pt–Pt interaction), molecular packing orientation, and electron transport ability are all influenced by the strong intermolecular hydrogen bonds. Consequently, the nondoped OLEDs based on tBu‐Pt and F‐Pt show electroluminescent emissions in NIR region with the highest external quantum efficiencies of 13.9% and 16.7%, respectively.

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“…1 To date, NIR OLEDs based on TADF organics, platinum(II) (Pt(II)) and osmium(II) (Os(II)) phosphors can achieve this goal. 5,[7][8][9][11][12][13] In general, the TADF emitter based NIR OLEDs exhibit very low luminance values to date. For example, by using an acenaphtho [1,2-b]pyrazine-8,9-dicarbonitrile (APDC) acceptor and two diphenylamine (DPA) donor units, Liao and co-workers synthesized NIR-emitting 3,4-bis(4-(diphenylamino)phenyl)ace-naphtho [1,2-b]pyrazine-8,9-dicarbonitrile (APDC-DTPA).…”

Section: Introductionmentioning

confidence: 99%

“…Remarkably, the efficiency roll-offs for these NIR OLEDs are nely restricted. 13 It seems that the Os(II) phosphors could be the best candidates for efficient and stable NIR OLEDs if the cost of the starting material dodecacarbonyltriosmium (Os 3 (CO) 12 ) is low. Therefore, these problems (such as low brightness values, serious efficiency roll-offs and high cost) will restrict the potential applications of these NIR-emitting materials and their electroluminescent (EL) devices.…”

Section: Introductionmentioning

confidence: 99%

A simple and efficient approach toward deep-red to near-infrared-emitting iridium(iii) complexes for organic light-emitting diodes with external quantum efficiencies of over 10%

et al. 2020

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Near infrared-emitting tris-bidentate Os(ii) phosphors: control of excited state characteristics and fabrication of OLEDs

Abstract: Os(ii) complexes bearing chromophoric 1,10-phenanthroline, diphosphine and bipyrazolate ancillaries display efficient NIR emission ranging from 717 nm to 779 nm in the solid state at RT.

Cited by 52 publications

References 84 publications

Observation of an Inversion in Photophysical Tuning in a Systematic Study of Luminescent Triazole-Based Osmium(II) Complexes

Observation of an Inversion in Photophysical Tuning in a Systematic Study of Luminescent Triazole-Based Osmium(II) Complexes

Enhancing Molecular Aggregations by Intermolecular Hydrogen Bonds to Develop Phosphorescent Emitters for High‐Performance Near‐Infrared OLEDs

A simple and efficient approach toward deep-red to near-infrared-emitting iridium(iii) complexes for organic light-emitting diodes with external quantum efficiencies of over 10%

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