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1. Bipyridine‐Containing Host Materials for High Performance Yellow Thermally Activated Delayed Fluorescence‐Based Organic Light Emitting Diodes with Very Low Efficiency Roll‐Off

   https://doi.org/10.1002/adom.201901283  

   Chen, Dongyang ; Rajamalli, Pachaiyappan ; Tenopala‐Carmona, Francisco ; Carpenter‐Warren, Cameron L. ; Cordes, David B. ; Keum, Chang‐Min ; Slawin, Alexandra M. Z. ; Gather, Malte C. ; Zysman‐Colman, Eli ( November 2019 , Advanced Optical Materials)

   Two bipolar host materials3‐CBPyand4‐mCBPyare reported. These hosts are structural analogs of the common host materials CBP and mCBP wherein the phenyl rings have been replaced with pyridines. The two materials possess deep highest occupied molecular orbital (HOMO) and shallow lowest unoccupied molecular orbital (LUMO) levels along with sufficiently high energyS₁andT₁states that make them suitable hosts for yellow emitters in electroluminescent devices. Yellow‐emitting thermally activated delayed fluorescence organic light‐emitting diodes are fabricated using 2,4,6‐tris (4‐(10H‐phenoxazin‐10‐yl)phenyl)‐1,3,5‐triazine (tri‐PXZ‐TRZ) as the dopant emitter with either3‐CBPyor4‐mCBPyemployed as the host. Their device performance is compared to analogous devices using CBP and mCBP as host materials. The pyridine‐containing host devices show markedly improved external quantum efficiencies (EQE) and decreased roll‐off. The 7 wt% tri‐PXZ‐TRZ‐doped device exhibits very low turn‐on voltage (2.5 V for both3‐CBPyand4‐mCBPy) along with maximum external quantum efficiencies (EQE_max) reaching 15.6% (for3‐CBPy) and 19.4% (for4‐mCBPy). The device using4‐mCBPyalso exhibits very low efficiency roll‐off with an EQE of 16.0% at a luminance of 10 000 cd m⁻².

    

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2. Seeing luminescence appear as crystals crumble. Isolation and subsequent self-association of individual [(C 6 H 11 NC) 2 Au] + ions in crystals

   https://doi.org/10.1039/d0sc03299a  

   Luong, Lucy M. ; Lowe, Christopher D. ; Adams, Alexandria V. ; Moshayedi, Venoos ; Olmstead, Marilyn M. ; Balch, Alan L. ( November 2020 , Chemical Science)

   null (Ed.)

   Non-luminescent, isostructural crystals of [(C 6 H 11 NC) 2 Au](EF 6 )·C 6 H 6 (E = As, Sb) lose benzene upon standing in air to produce green luminescent (E = As) or blue luminescent (E = Sb) powders. Previous studies have shown that the two-coordinate cation, [(C 6 H 11 NC) 2 Au] + , self-associates to form luminescent crystals that contain linear or nearly linear chains of cations and display unusual polymorphic, vapochromic, and/or thermochromic properties. Here, we report the formation of non-luminescent crystalline salts in which individual [(C 6 H 11 NC) 2 Au] + ions are isolated from one another. In [(C 6 H 11 NC) 2 Au](BArF 24 ) ((BArF 24 ) − is tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) each cation is surrounded by two anions that prohibit any close approach of the gold ions. Crystallization of [(C 6 H 11 NC) 2 Au](EF 6 ) (E = As or Sb, but not P) from benzene solution produces colorless, non-emissive crystals of the solvates [(C 6 H 11 NC) 2 Au](EF 6 )·C 6 H 6 . These two solvates are isostructural and contain columns in which cations and benzene molecules alternate. With the benzene molecules separating the cations, the shortest distances between gold ions are 6.936(2) Å for E = As and 6.9717(19) Å for E = Sb. Upon removal from the mother liquor, these crystals crack due to the loss of benzene from the crystal and form luminescent powders. Crystals of [(C 6 H 11 NC) 2 Au](SbF 6 )·C 6 H 6 that powder out form a pale yellow powder with a blue luminescence with emission spectra and powder X-ray diffraction data that show that the previously characterized [(C 6 H 11 NC) 2 Au](SbF 6 ) is formed. In the process, the distances between the gold( i ) ions decrease to ∼3 Å and half of the cyclohexyl groups move from an axial orientation to an equatorial one. Remarkably, when crystals of [(C 6 H 11 NC) 2 Au](AsF 6 )·C 6 H 6 stand in air, they lose benzene and are converted into the yellow, green-luminescent polymorph of [(C 6 H 11 NC) 2 Au](AsF 6 ) rather than the colorless, blue-luminescent polymorph. Paradoxically, the yellow, green-luminescent powder that forms as well as authentic crystals of the yellow, green-luminescent polymorph of [(C 6 H 11 NC) 2 Au](AsF 6 ) are sensitive to benzene vapor and are converted by exposure to benzene vapor into the colorless, blue-luminescent polymorph. 

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3. Unique prospects of phase change material Sb 2 Se 3 for ultra-compact reconfigurable nanophotonic devices

   https://doi.org/10.1364/OME.435979  

   Jia, Wei ; Menon, Rajesh ; Sensale-Rodriguez, Berardi ( August 2021 , Optical Materials Express)

   In this work, we explore inverse designed reconfigurable digital metamaterial structures based on phase change material Sb₂Se₃for efficient and compact integrated nanophotonics. An exemplary design of a 1 × 2 optical switch consisting of a 3 µm x 3 µm pixelated domain is demonstrated. We show that: (i) direct optimization of a domain containing only Si and Sb₂Se₃pixels does not lead to a high extinction ratio between output ports in the amorphous state, which is owed to the small index contrast between Si and Sb₂Se₃in such a state. As a result, (ii) topology optimization, e.g., the addition of air pixels, is required to provide an initial asymmetry that aids the amorphous state's response. Furthermore, (iii) the combination of low loss and high refractive index change in Sb₂Se₃, which is unique among all phase change materials in the telecommunications 1550 nm band, translates into an excellent projected performance; the optimized device structure exhibits a low insertion loss (∼1.5 dB) and high extinction ratio (>18 dB) for both phase states.

    

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4. 14-Electron Rh and Ir silylphosphine complexes and their catalytic activity in alkene functionalization with hydrosilanes

   https://doi.org/10.1039/D1DT00677K  

   Abeynayake, Niroshani S. ; Zamora-Moreno, Julio ; Gorla, Saidulu ; Donnadieu, Bruno ; Muñoz-Hernández, Miguel A. ; Montiel-Palma, Virginia ( August 2021 , Dalton Transactions)

   Herein we report an experimental and computational study of a family of four coordinated 14-electron complexes of Rh( iii ) devoid of agostic interactions. The complexes [X–Rh(κ 3 ( P,Si,Si )PhP( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 ], where X = Cl (Rh-1), Br (Rh-2), I (Rh-3), OTf (Rh-4), Cl·GaCl 3 (Rh-5); derive from a bis(silyl)- o -tolylphosphine with isopropyl substituents on the Si atoms. All five complexes display a sawhorse geometry around Rh and exhibit similar spectroscopic and structural properties. The catalytic activity of these complexes and [Cl–Ir(κ 3 ( P,Si,Si )PhP( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 ], Ir-1, in styrene and aliphatic alkene functionalizations with hydrosilanes is disclosed. We show that Rh-1 catalyzes effectively the dehydrogenative silylation of styrene with Et 3 SiH in toluene while it leads to hydrosilylation products in acetonitrile. Rh-1 is an excellent catalyst in the sequential isomerization/hydrosilylation of terminal and remote aliphatic alkenes with Et 3 SiH including hexene isomers, leading efficiently and selectively to the terminal anti-Markonikov hydrosilylation product in all cases. With aliphatic alkenes, no hydrogenation products are observed. Conversely, catalysis of the same hexene isomers by Ir-1 renders allyl silanes, the tandem isomerization/dehydrogenative silylation products. A mechanistic proposal is made to explain the catalysis with these M( iii ) complexes. 

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5. Non‐Volatile Reconfigurable Integrated Photonics Enabled by Broadband Low‐Loss Phase Change Material

   https://doi.org/10.1002/adom.202002049  

   Fang, Zhuoran ; Zheng, Jiajiu ; Saxena, Abhi ; Whitehead, James ; Chen, Yueyang ; Majumdar, Arka ( March 2021 , Advanced Optical Materials)

   Phase change materials (PCMs) have long been used as a storage medium in rewritable compact disk and later in random access memory. In recent years, integration of PCMs with nanophotonic structures has introduced a new paradigm for non‐volatile reconfigurable optics. However, the high loss of the archetypal PCM Ge₂Sb₂Te₅in both visible and telecommunication wavelengths has fundamentally limited its applications. Sb₂S₃has recently emerged as a wide‐bandgap PCM with transparency windows ranging from 610 nm to near‐IR. In this paper, the strong optical phase modulation and low optical loss of Sb₂S₃are experimentally demonstrated for the first time in integrated photonic platforms at both 750 and 1550 nm. As opposed to silicon, the thermo‐optic coefficient of Sb₂S₃is shown to be negative, making the Sb₂S₃–Si hybrid platform less sensitive to thermal fluctuation. Finally, a Sb₂S₃integrated non‐volatile microring switch is demonstrated which can be tuned electrically between a high and low transmission state with a contrast over 30 dB. This work experimentally verifies prominent phase modification and low loss of Sb₂S₃in wavelength ranges relevant for both solid‐state quantum emitter and telecommunication, enabling potential applications such as optical field programmable gate array, post‐fabrication trimming, and large‐scale integrated quantum photonic network.

    

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