A series of neutral tetradentate Pt(II) complexes with fused 6/5/6 metallocycles and biphenyl (bp)-containing ligands have been designed and synthesized. All bridging atoms adopt nitrogens designed as an acridinyl group (Ac), an aza acridinyl group (AAc), and an aza carbazolyl group (ACz), which can effectively tune their LUMO energy levels. Their HOMO energy levels can be well-controlled through molecular modifications on the bp moieties with electron-donating and electron-withdrawing groups. These molecular modifications also have profound effects on the electrochemical and photophysical properties and photostabilities of the Pt(II) complexes. The ground-states and excited states are systematically studied by density functional theory (DFT), timedependent density functional theory (TD-DFT), and natural transition orbital (NTO) calculations. All the Pt(II) complexes exhibit admixed 3 (LC/MLCT) characters in T 1 states with various proportions, which are strongly structure-dependent. These 6/5/6 Pt(II) complexes demonstrate high quantum efficiencies in dichloromethane solutions (Φ PL = 27−51%) and in doped PMMA films (Φ PL = 36−52%) at room temperature with short luminescence lifetimes of 1.6−9.5 μs and 7.6−9.0 μs, respectively. They emit green light with dominant peaks of 512−529 nm in solutions and 512−524 nm in doped PMMA films, respectively. Importantly, Pt(bp-2) exhibits highly stable emission colors with the same dominant peaks at 512 nm in various matrixes and also demonstrates a long photostability lifetime, LT 80 , at 80% of initial luminance, of 190 min, which is doped in polystyrene films (5 wt %) excited by UV light of 375 nm at 500 W/m 2 . These studies indicate that these 6/5/6 Pt(II) complexes can act as good phosphorescent emitters for OLED applications and should provide a viable route for the development of efficient and stable Pt(II)-based phosphorescent emitters.

A series of tetradentate Pt­(II) emitters containing fused 5/6/6 metallocycles have been designed and synthesized. Molecular geometries play a critical role in determining the photophysical properties. Their emission spectra are significantly affected by the geometries of the molecular core skeletons, the substituents, even hydrogen atoms, and their positions, which are further supported by X-ray crystallographic analyses and theoretical calculations. The generation of excimer emissions is observed in the tetradentate 5/6/6 Pt­(II) emitters for the first time and found to be concentration-dependent both in the solution and solid states. All of the Pt­(II) emitters have high photoluminescent quantum efficiency of up to 100% and luminescent lifetime as short as 1.4 μs at room temperature, achieving a radiative rate of 7.14 × 105 s–1. Their emission color can be easily tuned to cover the whole visible region (λmax = 464–632 nm) through selective synthetic modification of the heteroaromatic rings of the ligands. Pt­(1-ptz)-based sky blue organic light-emitting diode (OLED) demonstrates a maximum external quantum efficiency (EQE) of 14.5%, yet maintains an EQE of 12.7% at a high brightness of 1000 cd/m2. This work demonstrates that these tetradentate Pt­(II) complexes can act as efficient phosphorescent emitters for OLED applications.

Background and PurposeFew studies have reported on the risk factors of dilated Virchow-Robin Spaces (dVRS) in large samples of ischemic stroke patients. Little evidence exists regarding the relationship between dVRS and etiologic subtype of ischemic stroke or lacune. We aimed to investigate the risk factors associated with the severity of dVRS in a large sample of ischemic stroke patients.MethodsWe consecutively enrolled 1,090 patients who experienced an ischemic stroke within the past seven days and underwent a 3.0 T MRI scan in the Chinese IntraCranial AtheroSclerosis Study (ICAS). Clinical data and cranial MRI information of patients included age, sex, vascular risk factors, dVRS, leukoaraiosis, lacune, and etiologic subtype of ischemic stroke. Analyses were performed regarding the risk factors associated with the severity of dVRS by univariate analysis and multivariable ordinal logistic regression analysis.ResultsThrough multivariable ordinal logistic regression analysis, age, the severity of leukoaraiosis, lacune, admission National Institutes of Health Stroke Scale (NIHSS) ≤3, and the severity of dVRS in the white matter (WM) and hippocampus (Hip) were correlated with the severity of dVRS in basal ganglia (BG); male, history of hypertension, admission NIHSS ≤3, and the severity of dVRS in BG and Hip were correlated with the severity of dVRS in WM; female, the severity of leukoaraiosis, admission NIHSS >3, small artery occlusion subtype of ischemic stroke, and the severity of dVRS in BG and WM were correlated with the severity of dVRS in Hip.ConclusiondVRS is an indicator of cerebral small vessel diseases such as leukoaraiosis and lacune. However, the risk factors of dVRS differ in various brain regions.

The synthesis and photophysical characterization of a series of tetradentate cyclometalated M­(tzpPh-O-CzPy-R) complexes and their analogues are reported, where M is palladium or platinum and a tetradentate cyclometalating ligand contains tzpPh (3-phenyl-[1,2,4]­triazolo­[4,3-a]­pyridine) and CzPy (carbazolylpyridine) moieties linked with an oxygen atom. Variations of the σ-electron-donating group R on the ligand significantly affect the photophysical properties of the complexes. By using the strong electron-withdrawing tzp portion as an acceptor and the carbazole portion as a donor, a series of Pd­(II)-based metal-assisted delayed fluorescence (MADF) materials was developed. Electrochemical analysis demonstrates the irreversible reduction process occurs on the tzp ring and the irreversible oxidation process mainly occurs on the metal-phenyl moiety. This is in agreement with the HOMO and LUMO distributions by the DFT calculations, which also shows that the Pt­(II) complex has more metal orbital character than those of the Pd­(II) complexes. Most of the Pd­(II) complexes reported here are highly emissive at 77 K in 2-MeTHF with luminescent lifetimes in the millisecond range (τ = 1.96–2.36 ms) and λmax = 488–499 nm; however, the luminescent lifetimes are shortened to the microsecond range (τ = 26.7–152.9 μs in solution and 57.0–109.9 μs in thin film respectively) at room temperature. The quantum efficiency of the Pd­(II) complexes can be increased by more than 8-fold through structure modification with σ-donating groups on the ligand. Especially, the Pd­(tzp-3) has a small ΔE ST of 0.228 eV and exhibits strong typical MADF in PMMA film. The Pt­(II) complex Pt­(tzp-2) exhibits high thermal stability (ΔT 0.5% = 440 °C) and high quantum efficiency (Φ = 50.1%) in dichloromethane solution with τ of 15.8 μs. The Pt­(tzp-2) based bright green OLED achieved a peak EQE of 8.7% and a maximum brightness of 28280 cd/m2 using an unoptimized device structure.