Versatile Pt(II) Pyrazolate Complexes: Emission Tuning via Interplay of Chelate Designs and Stacking Assemblies

Ko, Chang‐Lun; Hung, Wen‐Yi; Chen, Po-Ting; Wang, Tsai-Hui; Hsu, Hsiu‐Fu; Liao, Jia-Ling; Ly, Kiet Tuong; Wang, Sheng Fu; Yu, Chung Huang; Liu, Shih-Hung; Lee, Gene‐Hsiang; Tai, Wun-Shan; Chou, Pi‐Tai; Chi, Yun

doi:10.1021/acsami.9b23388

Cited by 24 publications

(10 citation statements)

References 67 publications

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Section: Resultsmentioning

confidence: 99%

“…Recently, we have successfully prepared a series of Pt(II) pyrazolate complexes, to which the emission can be fine-tuned from sky blue to yellow by varying the concentration of Pt(II) emitters. 30 For further red shifting of the emission into the deep red and NIR region, Pt(II) complex 1 as an emitter was attained with a maximum external quantum efficiency (EQE) of 24% and a EL peak at 740 nm. 31 Via Pt(II) complexes 1−3 and their above doping concentration-dependent emission properties, now, we are capable of blue shifting the emission by simply diluting the titled Pt(II) complexes with an inert host material to systematically fine-tune the color from red to blue, i.e., an reverse direction of the conventional approach, while maintaining high device performance.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…In addition, [Pt(bppz) 2 ] with t -butyl substituents exhibited a lengthened Pt··· vector in crystal lattices, but [Pt(fppz) 2 ] with CF 3 substituents and derivatives revealed much shortened intermolecular Pt··· contact, governed by the reduced electron density at the Pt(II) metal center induced by the electron-accepting CF 3 substituent. Moreover, [Pt(fppz) 2 ] and analogues were also subject to the studies on interchanging among molecular designs, solid-state aggregation, and optoelectronic properties. ,− The relevant work included systematic investigation of structural and photophysical properties exerted by three isomeric Pt(II) complexes [Pt(pm2z) 2 ], [Pt(pm4z) 2 ], and [Pt(fprpz) 2 ], featuring 2-pyrimidinyl, 4-pyrimidinyl, and pyrazinyl coordination fragments. , Notably, an efficient NIR emission centered at 740 nm was clearly noted in [Pt(fprpz) 2 ] . Hence, these studies laid a solid foundation for a further development of OLED devices exhibiting emission spanning both visible and NIR regions. , …”

Section: Introductionmentioning

confidence: 99%

“…Later on, its functional pyrimidinebased Pt(II) complex [F−Pt] exhibited a solely red-shifted emission at 727 nm in a thin film, which is a combined result of higher crystallinity and enhanced intermolecular hydrogen bonds. 22 Analogously, several Pt(II) complexes featuring terdentate cyclometalate were examined (see Figure 1), 12 among which PtL 30 Cl with L 30 = 1,3-di(4-dimethylaminopyrid-2-yl)-4,6-difluorobenzene 23 exhibited a further blue-shifted emission in reference to those of PtL 26 Cl with L 26 = 1,3-di(4methoxypyrid-2-yl)-4,6-difluorobenzene, 24 giving white luminescence with a high color rendering index upon fabrication of OLED devices. Moreover, both the Pt(II) complexes [PtL 6 (NCS)], with L 6 = 5-mesityl-1,3-di(2-pyridyl)benzene and thiocyanate, 25 and [Pt(4-CF 3 −N∧C∧N)(CCPh)], with both CF 3 -substituted N∧C∧N chelate and acetylide, 26 have been found to exhibit a NIR emission beyond 800 nm, albeit having poor efficiency.…”

Section: ■ Introductionmentioning

confidence: 99%

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Luminescence of Pyrazinyl Pyrazolate Pt(II) Complexes Fine-Tuned by the Solid-State Stacking Interaction

Hung

et al. 2021

Energy Fuels

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Three functional pyrazinyl pyrazolate Pt(II) complexes [Pt(fprpz) 2 ] (1), [Pt(2fprpz) 2 ] (2), and [Pt(5fprpz) 2 ] (3), each with CF 3 , CF 2 H, and C 2 F 5 substituents on pyrazolate, were synthesized from treatment of Pt(DMSO) 2 Cl 2 and respective pyrazinyl pyrazole chelates (fprpz)H, (2fprpz)H, and (5fprpz)H in refluxing tetrahydrofuran solution. Variations of these fluorinated substituents provided a profound effect on both the photo-and electroluminescence properties of asprepared Pt(II) metal complexes in solution and solid states, respectively. More specifically, there exists a dominant ligand-centered 3 ππ* state contribution in both the solution state and doped thin films at a low concentration, which are strongly dependent upon the nature of the pyrazolate entity and tendency of self-aggregation. A systematic study demonstrates that the T 1 state properties can be fine-tuned by altering their functional substituents. Because Pt(II) complex 2 bears the least electron-deficient CF 2 H substituent, its thin film has shown the longest emissive wavelength in comparison to other derivatives. Upon formation of a vacuum-deposited thin film, the transition of the titled Pt(II) complexes is dominated by metal−metal-to-ligand charge transfer transition that can be tuned by the well-aligned stacking of the Pt(II) complexes, being more delocalized hence decreasing the energy upon increasing the stacking density. Moreover, we fabricated a series of organic light-emitting diodes (OLEDs) in an attempt to probe the concentration dependence of the doped emitter versus device performances. The electroluminescence of Pt(II) complex 1 shifted from sky blue to near infrared as the doping ratio gradually increased from 1 to 100 wt %. Broad-band white emission can also be realized by adjusting the concentration for optimal monomeric and aggregate emissions. With this remarkable feature, a highly efficient white OLED with external quantum efficiency up to 21.4% and spectral coverage from 450 to 800 nm was obtained at the doping level of 10 wt %, representing ideal candidates in developing solid-state lighting luminaries.

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Section: Resultsmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Luminescence of Pyrazinyl Pyrazolate Pt(II) Complexes Fine-Tuned by the Solid-State Stacking Interaction

Hung

et al. 2021

Energy Fuels

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“…In this regard, the formation of excimers is particularly notable for Pt(II) complexes bearing azolate chelates in solid states. − The resulting triplet excimers often possess significant metal–metal-to-ligand charge transfer ( 3 MMLCT) character, in which the electron is excited from a filled Pt···Pt d z 2 orbital with certain antibonding σ * character to a vacant π* orbital of the chelate. The energy of the MMCLT excited states has a strong dependence on the Pt···Pt interaction; i.e., the shortened interlayer distances correlate with lower MMLCT energies .…”

Section: Introductionmentioning

confidence: 99%

Formation of Excimers in Isoquinolinyl Pyrazolate Pt(II) Complexes: Role of Cooperativity Effects

et al. 2020

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The interplay between noncovalent interactions involving metal complexes may lead to the formation of aggregates (i.e., ground state dimers, trimers, n-mers, etc.), and this is often linked to dramatic changes in their physical and chemical properties as compared to the original properties of the isolated units. Dimers and trimers can also be formed in the excited state potential energy surfaces, i.e., excimers. Excimers are short-lived but are also often characterized by different optical properties from those of the isolated units. Understanding the nature of noncovalent interactions and the presence or not of cooperativity effects in both aggregates and excimers is thus extremely important to rationalize these variations. In this study, we present computational investigations on isoquinolinyl pyrazolate Pt(II) complexes. Our results highlight that cooperativity effects between noncovalent interactions, which are modulated by sterically demanding substituents and metallophilic Pt•••Pt interactions, are present only on certain investigated excimers. We use density functional theory (DFT) calculations to examine the cooperativity effects and the changes in the photophysical properties. Different descriptors of cooperativity effects between noncovalent interactions, including the synergetic, genuine nonadditive, and total interaction energies, were evaluated for a series of Pt(II) aggregates and excimers. In addition, energy decomposition analysis (EDA) calculations were performed to rationalize the origins of the cooperative effects. The cooperative effects in trimer excimers (in their lowest triplet excited state, i.e., T 1 ) led to shortened Pt••• Pt contacts as compared to the trimer aggregates. Furthermore, this synergy between noncovalent interactions is ultimately responsible for the formation of the excimers and the striking changes in the measured photophysical properties. More in detail, we report a change in the character of the lowest-lying triplet excited state when going from dimer excimers (i.e., of mixed triplet ligandcentered and triplet metal-to-ligand charge transfer ( 3 LC/ 3 MLCT) character) to trimer excimers (i.e., of triplet metal−metal-toligand charge transfer ( 3 MMLCT) character). The EDA reveals that the total interaction energy on trimer excimers is subtly controlled by the electrostatic and dispersion terms.

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Highly Efficient Near‐Infrared Electroluminescence up to 800 nm Using Platinum(II) Phosphors

Wang

Yuan

Wei

et al. 2020

Adv Funct Materials

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Near‐infrared organic light‐emitting diodes (NIR OLEDs) enable many unique applications ranging from night‐vision displays and photodynamic therapies. However, the development of efficient NIR OLEDs with a low efficiency roll‐off is still challenging. Here, a series of new heteroleptic Pt(II) complexes (1–4) flanked by both pyridyl pyrimidinate and functional azolate chelates are synthesized. The reduced ππ* energy gap of the pyridyl pyrimidinate chelate, and strong intermolecular interaction and high crystallinity in vacuum‐deposited thin films engender strong intermolecular charge transfer transition including metal–metal‐to‐ligand charge transfer; thereby, exhibiting efficient photoluminescence within 776–832 nm and short radiative lifetimes of 0.52–0.79 µs. Consequently, nondoped NIR‐emitting OLEDs based on these Pt(II) complexes are fabricated, to which Pt(II) complexes 2 and 4 give record high maximum external quantum efficiency of 10.61% at 794 nm and 9.58% at 803 nm, respectively. Moreover, low efficiency roll‐off is also observed, among which the device efficiencies of 2 and 4 are at least four times higher than that of the best NIR‐emitting OLEDs recorded at current density of 100 mA cm−2.

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Versatile Pt(II) Pyrazolate Complexes: Emission Tuning via Interplay of Chelate Designs and Stacking Assemblies

Cited by 24 publications

References 67 publications

Luminescence of Pyrazinyl Pyrazolate Pt(II) Complexes Fine-Tuned by the Solid-State Stacking Interaction

Luminescence of Pyrazinyl Pyrazolate Pt(II) Complexes Fine-Tuned by the Solid-State Stacking Interaction

Formation of Excimers in Isoquinolinyl Pyrazolate Pt(II) Complexes: Role of Cooperativity Effects

Highly Efficient Near‐Infrared Electroluminescence up to 800 nm Using Platinum(II) Phosphors

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