Intramolecular orbital engineered hetero bimetallic Ce-Fe MOF with reduced transition energy and enhanced visible light property

A structurally stable, 3d-4f heterometallic coordination polymer has been solvothermally synthesised and evaluated for its accomplished materials properties. The light absorption activity in the visible band was higher for unique Ce-Fe MOF than that of the homometallic Ce-MOF or Fe- MOF. The intimate overlap of two different metal clusters in heterometallic environmental induced the formation of low line conduction orbital, which ultimately lowered the transition energy. The heterometallic acquired an additional sensitisation from a Fe-μ3-oxo cluster that had vibrantly enhanced the light uptake activity. The vacancy created in the 6s, 5d orbital of Ce in Ce-Fe MOF contributed to the photo-excitation of electrons and reduced the recombination time. This distinct intramolecular arrangement assisted the exciton trapping characteristic. Also, the presence of multiple metal cores in the framework aided to confine the increased number of excitons for a redox reaction. The solar photocatalysis study with acetaminophen revealed these improved materialistic features by degrading it 94.6% with a rate constant of 0.0137 min⁻¹. The recycle studies confirmed the robust stability of the synthesised MOF.     

Transparent,Versatile Chemical Vapor Sensor Using Supramolecular Assembly of Block Copolymer and Carbon Nanotubes

Here, a simple and novel approach is reported for developing a new class of transparent chemical vapor sensors with a low power consumption, high sensitivity, good selectivity, and excellent environmental stability by depositing multiwalled carbon nanotubes on prepatterned polymer substrates using supramolecular assembly. The patterned polymer substrates were fabricated from block copolymers, whereas the supramolecular assembly between the carbon nanotubes and block copolymer is utilized for the selective localization of carbon nanotubes at the block copolymer–air interface. The thin film devices made from the block copolymer and carbon nanotubes are highly transparent (transmittance > 90%) and respond to a wide range of solvents of different polarity, both hydrophilic and hydrophobic, with good selectivity and fast response time.

     

Determination of the Association Constants of Charge-Transfer Complexes Between N,N-Diethylaniline and Nitro Explosives Using High Performance Thin Layer Chromatography with Scanning Video Densitometry and Spectrophotometry

Charge-transfer (CT) or electron donor-acceptor (EDA) complex formation between organic donors and acceptors has been extensively studied by spectrophotometry and other methods. High performance thin layer chromatography (HPTLC), although extensively used for the identification and quantification of drugs and explosives, has not been used until now to determine the extent of association and the association constants K _DA of charge transfer or EDA complexes between donor (D) and acceptor (A). This paper describes the use of the HPTLC technique with scanning densitometry to identify and determine the association constants K _DA of charge-transfer complexes of N,N-diethylaniline (DEA) with different nitro explosives, namely 1,4-dinitrobenzene (DNB), 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), in chloroform. Advantages of the HPTLC method are highlighted. The association constants K _DA of the complexes determined using the HPTLC method have been verified and validated spectrophotometrically when the concentrations of D and A are in their stoichiometric ratio. The thermodynamics of the complex formation reaction were obtained spectrophotometrically from measurements of the association constants K _DA at five different temperatures ranging from 293 to 313 K, when D and A are in their stoichiometric ratio and also when A≫D.     

Rhodium-catalysed chemo- and regio-selective [3 + 2+2] cycloadditions of bis(methylenecyclopropanes) and alkynes: Synthesis of spirocyclic 5–7 condensed cycloheptenes

Abstract

Rhodium-catalyzed intermolecular [3?+?2+2] cycloaddition reactions of bis(methylenecyclopropanes) with different alkynes are described. The rhodium-catalyzed [3?+?2+2] cycloadditions resulted in the formation of functionalized 5–7–3 spirocyclic carbocycles in moderate yields with excellent regio- and chemo-selectivity.     

Structural hierarchy in melt-processed poly(3-hexyl thiophene)-montmorillonite clay nanocomposites: novel physical, mechanical, optical, and conductivity properties

Poly(3-hexyl thiophene) (P3HT) organically modified montmorillonite (om-MMT) polymer nanocomposites (PNCs) are prepared in the melt-cooled state. Hierarchical structures up to third order, namely, side chain mesomorph formation followed by the interchain lamellar structure of P3HT and finally its intercalation within the clay tactoids are observed. The structures are supported by transmission electron microscopy (TEM) and wide-angle X-ray scattering (WAXS) experiments. The TGA curves show two-stage degradation corresponding to those of the side chain and main chain of P3HT, and both temperatures decrease with an increase in clay concentration in the PNCs. The melting points of PNCs have increased by 2-3 degrees C higher than that of P3HT. The glass-transition temperature (Tg) and beta-transition temperature (Tbeta), measured by DMA, increase with an increase in clay concentration. The storage modulus (G) of PNCs has also increased more dramatically than that of P3HT. The UV-vis spectra of the PNCs show a blue shift in the pi-pi* absorption peak of the conjugated chain, but the photoluminescence spectra showed a red shift with an increase in the clay concentration. The quantum yield of the photoluminescence process also increases in the melt-cooled PNCs, and this is in sharp contrast to that of solvent cast PNCs where photoluminescence quenching was observed. Fibrillar network structure of the solvent cast PNCs promotes energy transfer of the charge carriers, but its absence in the melt-cooled films inhibits such energy transfer, increasing the quantum yield. The room-temperature dc conductivity of the PNCs decreased by an order compared to that of P3HT in both the doped and undoped states. The I-V characteristic curve shows semiconducting behavior, and it slowly transforms into insulator with increasing clay concentration.     

Poly(3‐hexyl thiophene)‐b‐poly(N‐isopropyl acrylamide): Synthesis and its composition dependent structural,solubility, thermoresponsive,electrochemical, and electronic properties

Conjugated block copolymers consisting of poly(3‐hexyl thiophene) (P3HT) and a thermoresponsive polymer poly(N‐isopropyl acrylamide) (PNIPAM) with varying composition have been synthesized by facile click reaction between alkyne terminated P3HT and azide terminated PNIPAM. The composition‐dependent solubility, thermoresponsive property in water, phase behavior, electrochemical, optical, and electronic properties of the block copolymers were systematically investigated. The block copolymers with higher volume fraction of PNIPAM form thermoresponsive spherical micelles with P3HT‐rich crystalline cores and PNIPAM coronas. Both X‐ray and atomic force microscopic studies indicated that the blocks copolymers showed well‐defined microphase separated nanostructures and the structure depended on the composition of the blocks. The electrochemical study of the block copolymers clearly demonstrated that the extent of charge transport through the block copolymer thin film was similar to P3HT homopolymer without any significant change in the band gap. The block copolymers showed improved or similar charge carrier mobility compared with the pure P3HT depending on the composition of the block copolymer. These P3HT‐b‐PNIPAM copolymers were interesting for fabrication of optoelectronic devices capable of thermal and moisture sensing as well as for studying the thermoresponsive colloidal structures of semiconductor amphiphilic systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1785–1794     

pH and temperature responsiveness in AgNPs stabilized by a new poly(vinylidene fluoride) random graft copolymer

Poly(vinylidene fluoride)(PVDF)‐graft‐random copolymers(PD) of diethyleneglycol methylether methacrylate(MeO₂MA) and dimethylaminoethyl methacrylate(DMAEMA) are synthesized by a combined atom transfer radical coupling and atom transfer radical polymerization technique at three different co‐monomer compositions. The molar ratio of MeO₂MA to DMAEMA in PD are measured to be 1:5.8, 1:1.3, and 1:0.5 for PD1, PD2, and PD3 graft copolymers. In PD2 the feed ratio and mole ratio are same indicating an azeotropic composition causing highest yield (89%) and highest molecular weight (9.29 × 10⁵). The grafted chains of PD are temperature and pH responsive and in basic pH they show a sudden increase in size above certain temperature for LCST‐type phase transition, however, this is not observed at pH 4 and 7. PD can generate AgNPs under UV irradiation and morphology of PD at 30 °C varies with pH from vesicle to nanosphere. The AgNPs lie on the surface of the vesicles or assemble with the PD chains forming nanosphere morphology. At different pH, PD samples exhibit plasmon peaks at different wavelengths attributed to various size, shapes and cluster formation. The UV–vis spectra of AgNPs stabilized by PD1 and PD2 samples exhibits similar LCST‐type phase transition as observed above, but that of PD3 does not show any such transition. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 960–970     

Physical and electronic properties in multiwalled carbon nanotube–poly(3‐dodecylthiophene) nanocomposites

The properties of nanocomposites of dodecyl ester functionalized multiwalled carbon nanotube (FMWNT) and four poly(3‐dodecyl thiophene) (P3DDT) samples with different molecular weight and chain regioregularity are reported here. Uniform dispersion of FMWNT in the composites is evident from TEM study. π–π and CH–π interactions are evident from FTIR spectra in the low molecular weight (M_w = 8 × 10⁴) and high regiorandom (head‐tail = 69 mol %) P3DDT (ILM) composites; however, such interactions are not so prominent for other P3DDTs. Wide‐angle X‐ray scattering patterns indicate intact interchain lamellar structure of P3DDT in the composites. DSC study shows decrease of main chain melting peak of P3DDT (ILM) with increasing F‐MWNT content but the decrease is lower with higher molecular weight and higher regioregular samples. Dynamic mechanical analyzer study indicates that there is no significant change in the T_g, T_β, and T_γ transition temperature with FMWNT concentration indicating almost ideal mixing of the components. The percent increase of G′ increases with increasing FMWNT loading and also with temperature showing an 84% increase in storage modulus at –20 °C for ILM12 samples. The UV–vis spectrum indicates a decrease in band gap with FMWNT concentration for ILM composites, however, it is negligible with other P3DDTs. Photoluminescence quenching and multiple emission peaks occur in the composites. dc‐Conductivity of the composites increases by two orders and current‐voltage (I–V) curves show memory effect only in ILM‐MWNT composites. The I–V curves of other P3DDT nanocomposites exhibit rectification property. Quantitative explanation of electronic properties has been afforded from the band energy and work function values. So, the electronic properties of the nanocomposite can be tuned by changing the molecular weight, regioregularity, and concentration of FMWNT. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1412–1425, 2009     

Riemann solution for ideal isentropic magnetogasdynamics

In the present paper, we study the Riemann problem for quasilinear hyperbolic system of partial differential equations governing the one dimensional ideal isentropic magnetogasdynamics with transverse magnetic field. We discuss the properties of rarefaction waves, shocks and contact discontinuities. Differently from single equation methods rooted in the ideal gasdynamics, the new approach is based on the system of two nonlinear equations imposing the equality of total pressure and velocity, assuming as unknowns the two values of densities, on both sides of the contact discontinuity. Newton iterative method is used to obtain densities. The resulting exact solver is implemented with the examples of general applicability of the proposed approach. For comparisons with exact solution we also shown numerical results obtained by the total variation diminishing slope limiter centre scheme. It is shown that both analytical and numerical results demonstrate the broad applicability and robustness of the new Riemann solver.