Density functional theory study on antiferromagnetic interactions in a silver (I) complex of nitronyl nitroxide

A one-dimensional (1D) silver (I) complex of nitronyl nitroxide with fairly strong antiferromagnetic interaction, in which the metal ions are diamagnetic, is investigated by means of the ab initio crystal orbital method based on the density functional theory. The calculated values of the magnetic coupling constant (J) are close to the experimental measured J value in the periodic system. The magneto-structural correlation reveals that the existence of an antiferromagnetic coupling pathway along nitronyl nitroxide units via silver (I) ion in this system. The spin population distribution also shows the existence of spin delocalization along the ONCNO–Ag–ONCNO, which affords a rational interpretation for the antiferromagnetic interaction mechanism.     

Stable, reproducible nanorecording on rotaxane thin films

Stable, reversible conductance transitions and memory effects were observed in solid-state rotaxane-based Langmuir-Blodgett (LB) thin films. Taking advantage of the switching property, we have achieved reproducible nanometer-scale recording dots on rotaxane LB films via voltage application using a scanning tunneling microscope probe. The stable and easily controlled conductance switching makes the rotaxanes a hopeful candidate for nanorecording.     

SYNTHESES OF STYRENE-METHYL METHACRYLATE BLOCK COPOLYMER BY POLYAZOAMIDE AS INITIATOR

Polyazoamide(PAA) was used as initiator to prepare block copolymer P(MMA-b-St) byfree radical polymerization. The fraction of block copolymer was about 50%. The structureof the block-copolymer was characterized by IR and the results of ~1H-NMR and GPCshowed that the content of the block and the molecular weight (M_w) of the prepolymerand block copolymer could be controlled by varying the mol ratio of styrene/PAA andMMA/prepolymer. DSC and TEM results revealed that the block copolymer has twoseparated glass transition temperatures and phase separation within the domain structure.     

Fluoro-substituted DPP-bisthiophene conjugated polymer with azides in the side chains as ambipolar semiconductor and photoresist

Photoresists are essential for the fabrication of flexible electronics through all-photolithographic processes. Single component semiconducting photoresist exhibits both semiconducting and photo-patterning properties, and as a result, the device fabrication process can be simplified. However, the design of semiconducting polymeric photoresist with ambipolar semiconducting property remains challenging. In this paper, we report a single component semiconducting photoresist (PFDPPF4T-N₃) by incorporating azide groups and noncovalent conformation locks into the side alkyl chains and conjugated backbones of a diketopyrrolopyrrole-based conjugated polymer, respectively. The results reveal that PFDPP4FT-N₃ exhibits ambipolar semiconducting property with hole and electron mobilities up to 1.12 and 1.17 cm² V^?1 s^?1, respectively. Moreover, field effect transistors with the individual photo-patterned thin films of PFDPPF4T-N₃ also show ambipolar semiconducting behavior with hole and electron mobilities up to 0.66 and 0.80 cm² V^?1 s^?1, respectively. These results offer a simple yet effective design strategy for high-performance single component semiconducting photoresists, which hold great potential for flexible electronics processed by all photolithography.

     

Concatenation of two molecular switches via a Fe(II)/Fe(III) couple

[reaction: see text] Modulation of the fluorescein fluorescence in the presence of spiropyran and ferric ion by light was observed. Such fluorescence modulation was due to the low oxidation potential of complex MC.Fe(2+), which made the electron transfer from MC.Fe(2+) to Flu(+)()(*)() thermodynamically favorable. As a result, the communication between two molecular switches based on fluorescein and spiropyan, respectively, was realized via the reversible Fe(III)/Fe(II) redox couple. The communicating behavior corresponds well to the function of an INHIBIT logic gate.     

Transition metal coordination polymers with polycarboxylic acid as bridging ligands: Synthesis and structure characterization of [Fe(μ4-bta)0.5(phen)(OH)]<Subscript>n</Subscript>

A new 2D (two-dimensional) coordination polymer, [Fe(μ4-bta)o.5(phen)(OH)]_n (1), has been hydrothermally synthesized with FeCl₃ 6H₂, Na₄bta (h₄bta = 1,2,4,5-benzentetracarboxylic acid), 1,10-phen (1,10-phenanthroline) and H₂O as raw materials. The crystals of the compound belong to monoclinic P2₁/n space group, a = 1.0129(2) nm, b = 0.9265(2) nm, c = 1.5696(3) nm, β=91.37(3)°V=1.4721(5) nm³,Z=3, final R₁=0.0292, wR ₂=0.0798 for 2572 [/>2σ(/)] observed reflections. The result of structure determination shows that in the compound each bta ligand is connected with four Fe³, forming a new μ4-coordination mode. Four deprotonated carboxylic groups of bta link to Fe³ ions alternatively through monodentate and bidentate coordination fashion, constructing 2D layer network. The measurement of variable temperature magnetic susceptibility indicates that there exist antiferromagnetic interactions between Fe³ ions in the compound. The TGA spectrum displays relatively fine thermal stability of the compound. In addition, IR and UV-Vis spectra of compound 1 have also been measured.     

Synthesis and thermal modulation of the fluorescence of a pyrene-arylmaleimide dyad and its Diels-Alder adduct

The fluorescence of a pyrene-arylmaleimide dyad and its Diels-Alder adduct can be thermally modulated through reversible Diels-Alder reaction of arylmaleimide unit with furan. Moreover, the fluorescence intensities of the Diels-Alder adduct of dyad 1 with furan vary linearly with the temperatures of the corresponding solutions, demonstrating that these molecules are interesting compounds for studies of fluorescent molecular thermometers.     

Thermal degradation kinetics and heat properties of cellulosic cigarette paper: influence of potassium carboxylate as combustion improver

Accurate determination of the thermal properties of cellulose is of particular significance in studying the mechanism of cellulosic cigarette paper combustion. This paper probes into the influence of four kinds of potassium carboxylates on the thermal degradation kinetics and the heat properties of cigarette paper through simultaneous thermogravimetric analysis (TGA) coupled with differential scanning calorimetry (DSC) measurement under air atmosphere. Reduced mass loss and mass loss rate, and increased solid residue for samples containing four potassium salts implied that potassium carboxylates may retard the formation of levoglucosan and volatiles by inhibiting the depolymerization reaction and simultaneously accelerate char formation by catalyzing the dehydration reaction. Kinetic parameters were analyzed based on three non-isothermal models available in literature. The results indicated that three modeling methods exhibit good consistency. A global activation energy range of 106–155 kJ mol^?1 was proposed for cigarette paper with potassium carboxylates. The four potassium salts studied considerably reduced the activation energy in the following descending order: potassium 1,2,3,4-butane tetracarboxylate (PBTCA) > citrate > gluconate > ascorbate. The heat properties of cigarette paper were also determined by integrating the DSC curves. The results demonstrated that both cellulose degradation and char oxidation have strong exothermic peaks. Cigarette paper samples with potassium salts have lower exothermic cellulose degradation process and higher exothermic char oxidation process, which were further confirmed by greater differences as the amounts of salt citrate or PBTCA increased.     

One-step synthesis of novel flower-like Sn-doped ZnO architectures with enhanced photocatalytic activity

A facile hydrothermal method to synthesize flower-like Sn-doped ZnO (FLSn-ZnO) nanostructures is described. The obtained hierarchical architectures of FLSn-ZnO are found to be assembled with abundant regular-shaped nanosheets and nanoparticles. A possible formation mechanism is proposed on the base of a series of control experiments. The tests show that FLSn-ZnO architectures exhibit higher photocatalytic activity in the degrading Rhodamine B and tetracycline aqueous solution than pure ZnO under UV-light irradiation. And photocurrent response and photoluminescence of ZnO and FLSn-ZnO demonstrates that in photocatalytic performance, the latter is higher.