Temporary Silicon Tether Strategy for Palladium-Catalyzed C-H Activation Reactions

A palladium-catalyzed intramolecular ortho C–H arylation of phenols has been developed. This methodology features the employment of a removable silicon tether strategy, allowing both TBDPS and a newly developed Br-TBDPS protecting groups to serve as efficient aryl group donors for arylation of phenols. Along this line, this removable silicon tether strategy was further applied to the intramolecular arylation of bisaryloxysilanes for the preparation of unsymmetrical ortho-biphenols, ortho-binaphthols, and mixed ortho-phenol-naphthols. We have also developed a silanol-directed, palladium-catalyzed C–H alkenylation of phenols. Thus, employment of silanol as a traceless directing group is very convenient as it can easily be installed and removed under mild conditions. This alkenylation method is general, as it tolerates a variety of differently substituted phenols and diverse electron-deficient alkenes. The synthetic usefulness of this novel transformation was demonstrated in the efficient synthesis of benzofuranone derivative. Furthermore, the application of this method to the olefination of estrone showcased the viability of this method for the late-stage modification of bioactive molecules for drug discovery. Mechanistic studies supported an electrophilic pathway for the C–H activation step. We have also shown that silanol can direct palladium-catalyzed C–H oxygenation of phenols en route to catechols. This protocol is highly site selective and general, as it allows for efficient oxygenation of phenols regardless of their electronic properties. Mechanistic studies indicated that this C–H oxygenation reaction undergoes ortho C–H acetoxylation first, the product of which is then converted into the cyclic silyl-protected catechol via a transesterification/cyclization sequence mediated by the in situ generated acetic acid

Synthesis of Catechols from Phenols via Pd-Catalyzed Silanol-Directed C–H Oxygenation

A silanol-directed, Pd-catalyzed C–H oxygenation of phenols into catechols is presented. This method is highly site selective and general, as it allows for oxygenation of not only electron-neutral but also electron-poor phenols. This method operates via a silanol-directed acetoxylation, followed by a subsequent acid-catalyzed cyclization reaction into a cyclic silicon-protected catechol. A routine desilylation of the silacyle with TBAF uncovers the catechol product

Mitochondria-Directed Fluorescent Probe for the Detection of Hydrogen Peroxide near Mitochondrial DNA

It is important to detect hydrogen peroxide (H₂O₂) near mitochondrial DNA (mtDNA) because mtDNA is more prone to oxidative attack than nuclear DNA (nDNA). In this study, a mitochondria-targeted fluorescence probe, <b>pep3-NP1</b>, has been designed and synthesized. The probe contains a DNA-binding peptide, a H₂O₂ fluorescence reporter, and a positively charged red emissive styryl dye to facilitate accumulation in mitochondria. Due to groove binding of the peptide with DNA, the styryl dye of <b>pep3-NP1</b> intercalated into the bases of DNA, leading to an increase in red fluorescence intensity (centered at 646 nm) and quantum yield. In this case, <b>pep3-NP1</b> was a turn-on probe for labeling DNA. Subcellular locations of <b>pep3-NP1</b> and MitoTracker suggested that <b>pep3-NP1</b> mostly accumulated in the mitochondria of live cells. Namely, as an intracellular DNA marker, <b>pep3-NP1</b> bound to mtDNA. In the presence of H₂O₂, <b>pep3-NP1</b> emitted green fluorescence (centered at 555 nm). Thus, the ratio of green with red fluorescence of <b>pep3-NP1</b> was suitable to reflect the change of the H₂O₂ level near mtDNA in living cells. The detecting limit for H₂O₂ was estimated at 2.9 and 5.0 μM in vitro and in cultured cells, respectively. The development of <b>pep3-NP1</b> could help in studies to protect mtDNA from oxidative stress

Solution-Processed CuS NPs as an Inorganic Hole-Selective Contact Material for Inverted Planar Perovskite Solar Cells

Organic–inorganic hybrid perovskite solar cells (PSCs) have drawn worldwide intense research in recent years. Herein, we have first applied another p-type inorganic hole-selective contact material, CuS nanoparticles (CuS NPs), in an inverted planar heterojunction (PHJ) perovskite solar cell. The CuS NP-modification of indium tin oxide (ITO) has successfully tuned the surface work function from 4.9 to 5.1 eV but not affect the surface roughness and transmittance, which can effectively reduce the interfacial carrier injection barrier and facilitate high hole extraction efficiency between the perovskite and ITO layers. After optimization, the maximum power conversion efficiency (PCE) has been over 16% with low <i>J</i>–<i>V</i> hysteresis and excellent stability. Therefore, the low-cost solution-processed and stable CuS NPs would be an alternative interfacial modification material for industrial production in perovskite solar cells

CuSCN-Based Inverted Planar Perovskite Solar Cell with an Average PCE of 15.6%

Although inorganic hole-transport materials usually possess high chemical stability, hole mobility, and low cost, the efficiency of most of inorganic hole conductor-based perovskite solar cells is still much lower than that of the traditional organic hole conductor-based cells. Here, we have successfully fabricated high quality CH₃NH₃PbI₃ films on top of a CuSCN layer by utilizing a one-step fast deposition-crystallization method, which have lower surface roughness and smaller interface contact resistance between the perovskite layer and the selective contacts in comparison with the films prepared by a conventional two-step sequential deposition process. The average efficiency of the CuSCN-based inverted planar CH₃NH₃PbI₃ solar cells has been improved to 15.6% with a highest PCE of 16.6%, which is comparable to that of the traditional organic hole conductor-based cells, and may promote wider application of the inexpensive inorganic materials in perovskite solar cells

Amphiphilic PEGylated Lanthanide-Doped Upconversion Nanoparticles for Significantly Passive Accumulation in the Peritoneal Metastatic Carcinomatosis Models Following Intraperitoneal Administration

Inorganic nanoparticles have emerged as attractive materials for cancer research, because of their exceptional physical properties and multifunctional engineering. However, inorganic nanoparticle accumulation in the tumors located in the abdominal cavity after intravenous (IV) administration is confined because of the peritoneum–plasma barrier. To improve this situation, we developed lanthanide-doped upconversion nanoparticles (UCNPs), coated by amphiphilic polyethylene glycol (P-PEG), serving as a representative of inorganic nanoparticles. Following intraperitoneal (IP) administration into the peritoneal metastatic carcinomatosis models, UCNPs coated by P-PEG (P-PEG-UCNPs) passively accumulated in the cancerous tissues at a larger amount than that in the main normal organs. On the basis of spatial proximity, P-PEG-UCNPs administrated via the IP route exhibited higher passive accumulation in the tumors in the abdominal cavity compared to that via the IV route. It is suggested that IP administration could be a promising strategy for inorganic nanoparticles to be efficaciously applied in peritoneal cancer research

Water-Soluble and Highly Luminescent Europium(III) Complexes with Favorable Photostability and Sensitive pH Response Behavior

Two highly luminescent and water-soluble Eu­(III) complexes, <b>Eu1</b> and <b>Eu2</b>, based on novel carboxyl-functionalized 1,5-naphthyridine derivatives 8-hydroxy-1,5-naphthyridine-2-carboxylic acid (<b>H</b>_<b>2</b><b>L1</b>) and 7-cyano-8-hydroxy-1,5-naphthyridine-2-carboxylic acid (<b>H</b>_<b>2</b><b>L2</b>), respectively, are designed and synthesized. The crystal structure of <b>Eu2</b> indicates that the central Eu­(III) ion is nine-coordinated by three tridentate ligands (O^N^O). Both <b>Eu1</b> and <b>Eu2</b> show strong luminescence in aqueous solution with quantum yields (lifetimes) of 28% (1.1 ms) and 14% (0.76 ms), respectively. The chelates display unique UV-light stability in solution and remain highly emissive after 100 min of strong UV irradiation (∼300 W·m^–2 at 345 nm). Moreover, they exhibit reversible luminescence intensity changes with varied pH values, and the response mechanism is investigated. “Turn-on” of the Eu­(III) emission upon increasing pH is realized by ligand structure change from keto to enol anion form, resulting in red-shifted absorption band and suppressed quenching from solvents and N–H vibration upon deprotonating. The results show that these novel Eu­(III) complexes are quite intriguing for potential application as bioimaging agents and pH probes

Quantum Yields over 80% Achieved in Luminescent Europium Complexes by Employing Diphenylphosphoryl Tridentate Ligands

Four tridentate europium­(III) complexes containing a diphenylphosphoryl group are prepared with strong bonding between the ligands and centered ion, convinced by crystal structures. Compared to their parent bidentate complexes, the tridentate complexes display improved and exceptionally high photoluminescence quantum yields (PLQYs) in powder (all over 80%, best 91%), as well as in a CH₂Cl₂ solution and poly­(methyl methacrylate) films, benefiting from compact, stable, and saturated coordination

Solid-State, Polymer-Based Fiber Solar Cells with Carbon Nanotube Electrodes

Most previous fiber-shaped solar cells were based on photoelectrochemical systems involving liquid electrolytes, which had issues such as device encapsulation and stability. Here, we deposited classical semiconducting polymer-based bulk heterojunction layers onto stainless steel wires to form primary electrodes and adopted carbon nanotube thin films or densified yarns to replace conventional metal counter electrodes. The polymer-based fiber cells with nanotube film or yarn electrodes showed power conversion efficiencies in the range 1.4% to 2.3%, with stable performance upon rotation and large-angle bending and during long-time storage without further encapsulation. Our fiber solar cells consisting of a polymeric active layer sandwiched between steel and carbon electrodes have potential in the manufacturing of low-cost, liquid-free, and flexible fiber-based photovoltaics

Simple and High Efficiency Phosphorescence Organic Light-Emitting Diodes with Codeposited Copper(I) Emitter

Phosphorescent copper­(I) complexes show great promise as emitters in organic light-emitting diodes (OLEDs). However, most copper­(I) complexes are neither soluble nor stable toward sublimation and, hence, not amenable to the typical methods to fabricate OLEDs. In this work, a compound 3-(carbazol-9-yl)-5-((3-carbazol-9-yl)­phenyl)­pyridine (CPPyC) was designed as both a good ligand and host matrix. Codeposition of CPPyC and copper iodide (CuI) gives luminescent films with photoluminescent quantum yields (PLQY) as high as 100%. A dimeric copper­(I) complex Cu₂I₂(CPPyC)₄ is formed in the thin film, characterized by X-ray absorption spectroscopy. A series of simple, highly efficient green-emitting OLEDs were demonstrated by using the codeposited film as an emissive layer. A device comprised of only CPPyC and CuI gave an external quantum efficiency (EQE) of 12.6% (42.3 cd/A) at 100 cd/m², while a device with tailored hole and electron transporting layers gave an efficiency of 15.7% (51.6 cd/A) at the same brightness