Oxysulfide Semiconductors for Photocatalytic Overall Water Splitting with Visible Light

Photocatalytic overall water splitting by sulfide‐based materials is a great challenge because of the poor resilience of such materials against hole oxidation. In a recent study, Domen and co‐workers developed an innovative strategy to stabilize sulfide‐based photocatalysts by hybridizing S 3p with O 2p orbitals to produce oxysulfides in which S^2? is stable. Further surface engineering of the oxysulfides with dual co‐catalysts promoted charge separation and interface transfer, thus reducing the charge build‐up that inhibits photocorrosion. The pH value of the reaction mixture is a critical consideration for achieving efficient stoichiometric H₂ and O₂ evolution by these oxysulfide photocatalysts.     

Correlating conductivity and Seebeck coefficient to doping within crystalline and amorphous domains in poly(3-(methoxyethoxyethoxy)thiophene)

Molecular doping of conjugated polymers (CPs) plays a vital role in optimizing organic electronic and energy applications. For the case of organic thermoelectrics, it is commonly believed that doping CPs with a strong dopant could result in higher conductivity (σ) and thus better power factor (PF). Herein, by investigating thermoelectric performance of a polar side-chain bearing CP, poly(3-(methoxyethoxyethoxy)thiophene) (P3MEET), vapor doped with fluorinated-derivative of tetracyanoquinodimethane FnTCNQ (n = 1, 2, 4), we show that using strong dopants can in fact have detrimental effects on the thermoelectric performance of CPs. Despite possessing higher electron affinity, doping P3MEET with F4TCNQ only results in a σ (27.0 S/cm) comparable to samples doped with other two weaker dopants F2TCNQ and F1TCNQ (26.4 and 20.1 S/cm). Interestingly, F4TCNQ-doped samples display a marked reduction in the Seebeck coefficient (α) compared to F1TCNQ- and F2TCNQ-doped samples from 42 to 13 μV/K, leading to an undesirable suppression of the PF. Structural characterizations coupled with Kang-Snyder modeling of the α–σ relation show that the reduction of α in F4TCNQ-doped P3MEET samples originates from the generation of low mobility carrier within P3MEET's amorphous domain. Our results demonstrate that factors such as dopant distribution and doping efficiency within the crystalline and amorphous domains of CPs should play a crucial role in advancing rational design for organic thermoelectrics.     

CO2 Electroreduction in Ionic Liquids: A Review

The increasing emission of carbon dioxide (CO₂) caused by the unrestrained consumption of fossil fuels in recent hundreds of years, has caused global environmental and social problems. Meanwhile, CO₂ is a cheap, abundant and renewable C1‐feedstock, which can be converted into alcohols, ethers, acids and other value‐added chemicals. Compared with the thermal reactions, electrochemical reduction of CO₂ is more attractive because of its advantages by using the seasonal, geographical and intermittent energy (tide, wind and solar) under mild conditions. In recent years, taking ionic liquids (ILs) as electrolytes in the CO₂ electrochemical reduction reaction has been paid much more attention due to the advantages of lowering the overpotential of CO₂ electroreduction and improving the Faradaic efficiency. In this paper, we summarized the recent progresses of electrochemical reduction of CO₂ in ILs electrolytes, and analyzed the reaction mechanism of CO₂ reaction in the electrode‐electrolyte interface region by experimental and simulation methods. Finally, the research which needs to be highlighted in this area was proposed.     

Charge transfer during H/H− collisions with Cu(100) and Cu(111) surfaces

We study the H and H⁻ survival probabilities during collisions with Cu(100) and Cu(111) surfaces, at energies ranging from 0.5 to 5 keV and exit angles ranging from 20° to 90°. Calculations are performed with the Wave‐Packet Propagation method adapted to ion‐surface interactions. The projectile survival probability depends on the perpendicular velocity and the copper face being investigated. Projectile's interaction time with the surface and the distance of closest approach are important factors that influence the survival. The H⁻ survival on Cu(100) is much smaller than on Cu(111) but only at low velocities, while becoming higher or comparable to Cu(111) for higher velocities. For very fast collisions, the copper surface behaves like a jellium, and the electron involved in charge transfer does not “feel” the particularities of the surface band structure anymore. While the H survival on Cu(100) seems to not depend on energy and exit angle, the H survival on Cu(111) is both energy and angle dependent, and it is smaller. The study of partial density of states indicates that strong atom‐surface interactions at short distances and the role played by surface states are important factors in determining the neutral fractions obtained after scattering.     

Fluoride anion sensing mechanism of a BODIPY‐linked hydrogen‐bonding probe

The sensing mechanism of a fluoride‐anion probe BODIPY‐amidothiourea ( 1c ) has been elucidated through the density functional theory (DFT) and time‐dependent density functional theory (TDDFT) calculations. The theoretical study indicates that in the DMSO/water mixtures the fluorescent sensing has been regulated by the fluoride complex that formed between the probe 1c /two water molecules and the fluoride anion, and the excited‐state intermolecular hydrogen bond (H‐B) plays an important role in the fluoride sensing mechanism. In the first excited state, the H‐Bs of the fluoride complex 1cFH₂ are overall strengthened, which induces the weak fluorescence emission. In addition, molecular orbital analysis demonstrates that 1cFH₂ has more obvious intramolecular charge transfer (ICT) character in the S₁ state than 1cH₂ formed between the probe 1c and two water molecules, which also gives reason to the weaker fluorescence intensity of 1cFH₂ . Further, our calculated UV‐vis absorbance and fluorescence spectra are in accordance with the experimental measurements. © 2018 Wiley Periodicals, Inc.     

Molecular weight dependence of carrier mobility and recombination rate in neat P3HT films

The microstructure dependence of carrier mobility and recombination rates of neat films of poly 3‐hexylthyophene (P3HT) were determined for a range of materials of weight‐average molecular weights, M_w, ranging from 14 to 331 kDa. This variation has previously been shown to modify the polymer microstructure, with low molecular weights forming a one‐phase, paraffinic‐like structure comprised of chain‐extended crystallites, and higher molecular weights forming a semicrystalline structure with crystalline domains being embedded in an amorphous matrix. Using Charge Extraction by Linearly Increasing Voltage (CELIV), we show here that the carrier mobility in P3HT devices peaks for materials of M_w = 48 kDa, and that the recombination rate decreases monotonically with increasing molecular weight. This trend is likely due to the development of a semicrystalline, two‐phase structure with increasing M_w, which allows for the spatial separation of holes and electrons into the amorphous and crystalline regions, respectively. This separation leads to decreased recombination. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 31–35     

The Role of Torsional Dynamics on Hole and Exciton Stabilization in π‐Stacked Assemblies: Design of Rigid Torsionomers of a Cofacial Bifluorene

Exciton and charge delocalization across π‐stacked assemblies is of importance in biological systems and functional polymeric materials. To examine the requirements for exciton and hole stabilization, cofacial bifluorene ( F 2) torsionomers were designed, synthesized, and characterized: unhindered (model) ^Me F 2, sterically hindered ^tBu F 2, and cyclophane‐like ^C F 2, where fluorenes are locked in a perfect sandwich orientation via two methylene linkers. This set of bichromophores with varied torsional rigidity and orbital overlap shows that exciton stabilization requires a perfect sandwich‐like arrangement, as seen by strong excimeric‐like emission only in ^C F 2 and ^Me F 2. In contrast, hole delocalization is less geometrically restrictive and occurs even in sterically hindered ^tBu F 2, as judged by 160 mV hole stabilization and a near‐IR band in the spectrum of its cation radical. These findings underscore the diverse requirements for charge and energy delocalization across π‐stacked assemblies.     

Isonitrile Formation by a Non‐Heme Iron(II)‐Dependent Oxidase/Decarboxylase

The electron‐rich isonitrile is an important functionality in bioactive natural products, but its biosynthesis has been restricted to the IsnA family of isonitrile synthases. We herein provide the first structural and biochemical evidence of an alternative mechanism for isonitrile formation. ScoE, a putative non‐heme iron(II)‐dependent enzyme from Streptomyces coeruleorubidus, was shown to catalyze the conversion of (R)‐3‐((carboxymethyl)amino)butanoic acid to (R)‐3‐isocyanobutanoic acid through an oxidative decarboxylation mechanism. This work further provides a revised scheme for the biosynthesis of a unique class of isonitrile lipopeptides, of which several members are critical for the virulence of pathogenic mycobacteria.     

Tunable Chiroptical Properties from the Plasmonic Band to Metal–Ligand Charge Transfer Band of Cysteine‐Capped Molybdenum Oxide Nanoparticles

Understanding the interactions between a semiconducting nanocrystal surface and chiral anchoring molecules could resolve the mechanism of chirality induction in nanoscale and facilitate the rational design of chiral semiconducting materials for chiroptics. Now, chiral molybdenum oxide nanoparticles are presented in which chirality is transferred via a bio‐to‐nano approach. With facile control of the amount of chiral cysteine molecules under redox treatment, circular dichroism (CD) signals are generated in the plasmon region and metal–ligand charge‐transfer band. The obtained enhanced CD signals with tunable lineshapes illustrate the possibility of using chiral molybdenum oxide nanoparticles as potentials for chiral semiconductor nanosensors, optoelectronics, and photocatalysts.