A Pyrrole Modified 3,4-Propylenedioxythiophene Conjugated Polymer as Hole Transport Layer for Efficient and Stable Perovskite Solar Cells.

Despite the outstanding electric properties and cost-effectiveness of poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives, their performance as hole transport layer (HTL) materials in conventional perovskite solar cells (PSCs) has lagged behind that of widely used spirobifluorene-based molecules or poly(triaryl amine). This gap is mainly from their poor solubility and energy alignment mismatch. In this work, the design and synthesis of a pyrrole-modified HTL (PPr) based on 3,4-propylenedioxythiophene (ProDOT) are presented for efficient and stable PSCs. As a result of the superior defects passivation ability, excellent contact with perovskite, enhanced hole extraction, and high hydrophobicity, the unencapsulated PPr-based PSCs showed the peak PCE of 21.49% and outstanding moisture stability (over 4000 h). This work highlights the potential application of ProDOT-based materials as HTL for PSCs and underscores the importance of the rational design of PEDOT and its derivatives.

Oxidative Cleavage of Aromatic C-O Linkages by Oxoammonium Salts.

Oxidative cleavage of aromatic C(sp2)-O bond is important to the conversion of biomass and plastic wastes into value-added chemicals. Here we put forward the oxidative cleavage of para-C-O bonds in phenolic compounds in use of oxoammonium salts as oxidant and water as the oxygen source. The mechanism is that oxoammonium cation activates water to form hydroxy-oxoammonium adduct and thus realizes the ipso-substitution of 4-alkoxyphenol, which is proved by substituent effect, isotope labelling experiments, and kinetic analysis. Furthermore, this protocol is successfully applied into the depolymerization of both lignin model compounds with α-O-5 and 4-O-5 linkages and polyphenylene oxide (PPO).

Oxygenation of Phenols with Water as the Oxygen Source and Oxoammonium Salt as the Oxidant.

Aromatic C-H oxygenation is important in both industrial production and organic synthesis. Here we report a metal-free approach for phenol oxygenation with water as the oxygen source using oxoammonium salts as the renewable oxidant. Employing this protocol, various alkyl-substituted phenols were converted into benzoquinones in yields of 59-98%. On the basis of 18O-labeling and kinetic studies, the hydroxy-oxoammonium adduct was proposed to attack the aromatic ring similarly to electrophilic aromatic substitution. We suppose that the findings described here not only provide an efficient and highly selective protocol for aromatic C-H oxygenation but also may encourage further developments of possible transition-metal-free catalytic methods.

Circularly Recyclable Polymers Featuring Topochemically Weakened Carbon-Carbon Bonds.

Closed-loop circular utilization of plastics is of manifold significance, yet energy-intensive and poorly selective scission of the ubiquitous carbon-carbon (C-C) bonds in contemporary commercial polymers pose tremendous challenges to envisioned recycling and upcycling scenarios. Here, we demonstrate a topochemical approach for creating elongated C-C bonds with a bond length of 1.57∼1.63 Å between repeating units in the solid state with decreased bond dissociation energies. Elongated bonds were introduced between the repeating units of 12 distinct polymers from three classes. In all cases, the materials exhibit rapid depolymerization via breakage of the elongated bond within a desirable temperature range (140∼260 °C) while otherwise remaining remarkably stable under harsh conditions. Furthermore, the topochemically prepared polymers are processable and 3D-printable while maintaining a high depolymerization yield and tunable mechanical properties. These results suggest that the crystalline polymers synthesized from simple photochemistry and without expensive catalysts are promising for practical applications with complete materials' circularity.

Side-Chain Control of Topochemical Polymer Single Crystals with Tunable Elastic Modulus.

Topochemical polymerizations hold the promise of producing high molecular weight and stereoregular single crystalline polymers by first aligning monomers before polymerization. However, monomer modifications often alter the crystal packing and result in non-reactive polymorphs. Here, we report a systematic study on the side chain functionalization of the bis(indandione) derivative system that can be polymerized under visible light. Precisely engineered side chains help organize the monomer crystals in a one-dimensional fashion to maintain the topochemical reactivity. By optimizing the side chain length and end group of monomers, the elastic modulus of the resulting polymer single crystals can also be greatly enhanced. Lastly, using ultrasonication, insoluble polymer single crystals can be processed into free-standing and robust polymer thin films. This work provides new insights on the molecular design of topochemical reactions and paves the way for future applications of this fascinating family of materials.

Control of Selectivity in FeCl3 -Catalyzed Aerobic Oxidation of Cycloketones.

The FeCl3 -catalyzed aerobic oxidation of ketones always gives rise to the α-C-C cleavage product, having challenges to afford hydroxyl keto compounds. Here we report an effective control of the main product from keto acid to α-hydroxyl ketone, by reducing the concentration of FeCl3 catalyst, together with the use of DMSO as the solvent. In addition, mechanistic investigations suggested the same FeCl3 -coordinated peroxide intermediate for both hydroxylation and C-C cleavage routes, and emphasize the role of DMSO as both ligand and reductant. This work provides a new approach for selective aerobic oxidation under Lewis acid catalysis.

A selenophene-containing conjugated organic ligand for two-dimensional halide perovskites.

A selenophene-containing conjugated organic ligand, 2-(4'-methyl-5'-(5-(3-methylthiophen-2-yl)selenophen-2-yl)-[2,2'-bithiophen]-5-yl)ethan-1-aminium (STm), was synthesized and incorporated into a Sn(II)-based two-dimensional perovskite, (STm)2SnI4. The band offset between the perovskite and ligand can be fine-tuned by introducing the STm ligand. Both field-effect transistor and light-emitting diode devices based on (STm)2SnI4 films exhibit high performance and enhanced operational stability.

Three Lanthanide Metal-Organic Frameworks Based on an Ether-Decorated Polycarboxylic Acid Linker: Luminescence Modulation, CO2 Capture and Conversion Properties.

Three new isostructural 3D lanthanide metal-organic frameworks (Ln-MOFs), {H[LnL(H2 O)]⋅2 H2 O}n (1-Ln) (Ln=Eu3+ , Gd3+ and Tb3+ ), based on infinite lanthanide-carboxylate chains were constructed by employing an ether-separated 5,5'-oxydiisophthalic acid (H4 L) ligand under solvothermal reaction. 1-Eu and 1-Tb exhibit strong red and green emission, respectively, through the antenna effect, as demonstrated through a combination of calculation and experimental results. Moreover, a series of dichromatic doped 1-Eux Tby MOFs were fabricated by introducing different concentrations of Eu3+ and Tb3+ ions, and they display an unusual variation of luminescent colors from green, yellow, orange to red. 1-Eu with channels decorated by ether O atoms and the open metal sites displays good performance for CO2 capture and conversion between CO2 and epoxides into cyclic carbonates.