Latest ArticlesThe effects of concentration and an oriented external electric field on the transformations of hydrogenbonded structures of trimesic acid (TMA) and terephthalic acid (TPA) have been investigated at a liquid–solid interface by scanning tunneling microscopy (STM). The triangular periodic TMA framework can be transformed into a flower-like structure by changing the STM sample bias sign in situ. Networks of TMA and TPA are porous at a negative substrate bias, but typically change to relatively compact forms when the polarity of the applied bias is reversed. This change is reversible if the applied bias is reversed. The effects have potentials to locally control the capture and release of analytes in host-guest systems and the 2D morphology in multicomponent layers.
Proppant is a key material in the hydraulic fracturing process, which has been widely used in unconventional oil exploitation. Normal proppants are easy to sedimentate and accumulate at the entrance of shale fracture, which will block the diversion of water, oil and gas. Coated proppants (CPs) are fabricated by coating resin on normal ceramic proppants through a simple method, which is dramatically enhanced the supporting properties in shale fracture and easy to scale up. Compared with uncoated ceramic proppants, the self-suspension ability of CPs is ~11 times higher, which are able to migrate and distribute farther and deeper inside the fracture. At the same time, Coating enhanced the 23.7% of adhesive force in maximum, which makes the CPs easier to adhere on the fracture surface to supportthe shale fracture. Besides, the liquid conductivity of CPs is 60% higher than uncoated ceramic proppants at 13.6 MPa pressure. This method is expected to fabricated varieties of proppantsfor shale fracture supporting to improve the exploration of unconventional oil and gas resources.
A Mn(Ⅲ) mediated radical reaction of new designed multi-functionalized 2-isocyano-6-alkenyl(alkynyl) benzonitriles with arylboronic acids has been developed. This reaction provides a method for the synthesis of pyrroloisoquinoline derivatives through the formation of two C—C bonds and one C—N bond via radical cascade cyclization in one step.
Water-soluble thermoresponsive polymers present either upper critical solution temperature (UCST) or lower critical solution temperature (LCST) depending on the location of their miscibility range with water at high temperatures or at low temperatures. Compared with LCST polymers, the water-soluble UCST polymers are still less explored until now. In this work three copolymers of P(AAm-co-GAA) were synthesized by copolymerizing two acrylamide monomers, acrylamide (AAm) and acrylamide functionalized with natural glycyrrhetinic acid (GAA), using reversible addition-fragmentation chain transfer (RAFT) polymerization. These copolymers exhibited the typical UCST thermoresponsive behavior, and their phase transition temperatures could be easily tuned to around 37 ℃ for potential biological applications. Moreover, the UCST of P(AAm-co-GAA) can be adjusted not only by the content of glycyrrhetinic acid (GA) and polymer concentrations, but also by the host-guest interactions between GA and cyclodextrins (β- and γ-CD). The suitable value of UCST and the biocompatible nature of GA and CDs may endow these copolymers with practical applications in biomedical chemistry
Two types of palladium(Ⅱ)-based metallacalixarenes [ML]2+ and [ML2]2+ have been synthesized through coordination-driven self-assembly from a series of flexible pyridine-bridged diimidazole ligands [2,6-bis ((1H-imidazol-1-yl)methyl) pyridine (L1), 2,6-bis((1H-benzo[d]imidazol-1-yl)methyl)pyridine (L2), 2,6-bis((1H-naphtho[2,3-d]imidazol-1-yl)methyl)pyridine (L3)], with palladium(Ⅱ)-based building blocks [Pd(BF4)2(M1-BF4) and (tmeda)Pd(NO3)2 (M2-NO3) (tmeda = N, N, N', N'-tetramethyl-ethylenediamine)]. All complexes were characterized by NMR spectroscopy (1H NMR and 13C NMR), mass spectrometry (CSI-MS, ESI-HRMS) and elemental analysis. The single crystal X-ray diffraction analysis of [M1L22](NO3)2, [M1L23](NO3)2, [M1L23](PF6)2 and [M2L3](NO3)2 further confirmed the uniquely single bowl-shape and double bowl-shape structures. The anion binding properties within the metallacalixarenes as receptors were also investigated by NMR titration experiments in DMSO.
Polymorphism is a common phenomenon in nature. Here, we report one-pot wet chemical method to synthesize two polymorphs of Au19Ag4(S-Adm)15 nanocluster protected by 1-adamantanethiol (HS-Adm), which adopt P-1 and P21/c space group respectively. The crystal structures of two polymorphs were determined by X-ray crystallography. Compared to the previously reported Au19Ag4(S-Adm)15 nanocluster adopting P21/n space group, polymorphs of Au19Ag4(S-Adm)15 with P-1 and P21/c space group show the different optical properties. Moreover, Au19Ag4(S-Adm)15 with P-1 space group exhibits good thermal stability. Meanwhile, we investigated the effect of solvent and molar ratio of metal precursors on the polymorphs. This work provides an insight to polymorphs of metal nanoclusters.
The donor: acceptor (D: A) blend ratio plays a very important role in affecting the progress of charge transfer and energy transfer in bulk heterojunction (BHJ) organic solar cells (OSCs). The proper D: A blend ratio can provide maximized D/A interfacial area for exciton dissociation and appropriate domain size of the exciton diffusion length, which is beneficial to obtain high-performance OSCs. Here, we comprehensively investigated the relationship between various D: A blend ratios and the charge transfer and energy transfer mechanisms in OSCs based on PBDB-T and non-fullerene acceptor IT-M. Based on various D: A blend ratios, it was found that the ratio of components is a key factor to suppress the formation of triplet states and recombination energy losses. Rational D: A blend ratios can provide appropriate donor/accepter surface for charge transfer which has been powerfully verified by various detailed experimental results from the time-resolved fluorescence measurement and transient absorption (TA) spectroscopy. Optimized coherence length and crystallinity are verified by grazing incident wide-angle X-ray scattering (GIWAXS) measurements. The results are beneficial to comprehend the effects of various D: A blend ratios on charge transfer and energy transfer dynamics and provides constructive suggestions for rationally designing new materials and feedback for photovoltaic performance optimization in non-fullerene OSCs
Experiments indicate that a catalytic amount of CuI plays an important role in the siloxane-mediated Pd-catalyzed cross-coupling reactions with the direct use of organolithium reagents. Addition of organolithium to the siloxane transfer agent generates an organosilicon intermediate. DFT calculations indicate that CuI initially accelerates the Si-Pd(Ⅱ) transmetalation of the organosilicon intermediate by the formation of CuI2-. Subsequently, CuI2- works as a shuttle between the Si-Cu(I) and Cu(I)-Pd(Ⅱ) transmetalation processes.
In this work, a blue emitter with a 3D rigid structure composed of multiple spirobifluorene (3-Spiro) has been synthesized and characterized. Through a detailed study of the electrochemical and photophysical properties of 3-Spiro, we have evidenced that 3-Spiro can be applied as an active component of organic light-emitting diodes (OLEDs). The device with 5% doping rate of 4CzPNPh exhibits high external quantum efficiency (EQE) of 11%, which proves the potential of 3D rigid structure emitters for OLEDs.
A rhodium-catalyzed directing group promoted selective C–H olefination reaction of indolizines at the 8-position is reported. Di-olefination at 2,8-positions also achieved with silver hexafluoroantimonate as an additive under similar reaction conditions. Weakly coordinating groups, such as ketone, aldehyde, amide and ester, were used as directing groups. The ester group can be removed under acid conditions and therefore is used as a traceless directing group.
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