The role of segregation in the polarized emission from polyfluorene embedded in a liquid crystal

Polyfluorene (PFO) embedded in a nematic liquid crystal (LC) matrix is investigated. For low PFO weight contents, a homogeneous dispersion is obtained which displays a strong fluorescence anisotropy along the LC director, indicating a significant alignment of the polymeric chains along this direction. Besides, for relatively high PFO weight contents, phase separation takes place. Under these conditions, the sample is composed of micrometer‐sized domains, where the two species are in solution, enclosed by segregated polymeric boundaries. By polarized‐photoluminescence imaging and spectroscopy, it is found that most of the light emission originates from these boundaries and gets strongly pinned along their orientation. Since boundaries are mainly oriented orthogonal to the LC chains, this morphological alignment results in a system in which the orientation of the polarization emission can be predicted and possibly controlled. Conversely, in the homogeneous sample one can obtain a homogeneous emission polarization by controlling the alignment of the LC. These features are potentially relevant for the development of flexible polarization‐sensitive optoelectronic devices. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1558–1563     

Seamless Rim‐Functionalization of h‐BN with Silica—Experiment and Theoretical Modeling

Boron nitride contains six‐ring layers, which are isostructural to graphene, and it exhibits similar extraordinary mechanical strength. Unlike graphene, hexagonal boron nitride (h‐BN) is an insulator and has some polar features that make it a perfect material for those applications graphene is not suitable for, for example, purely ionic conductors, insulating membranes, transparent coatings, composite ceramics, high oxidation resistance materials. We report here a selective rim‐functionalization of h‐BN with SiO₂ by using the Stöber process. A closed, protruding ring of SiO₂ is formed covering all edges perpendicular to the [001] zones of the h‐BN stacks and thus shield the most reactive centers of BN layers. SEM and HAADF‐STEM images, X‐ray spectroscopy, and atomic force microscopy confirm the rim‐functionalization by SiO₂. XRD demonstrates the absence of any intercalation phenomenon of BN and reveals the glassy nature of the SiO₂ rims. Selected variations of synthesis and theoretical modeling both confirm that rim activation by water prior to the Stöber condensation is crucial. First‐principles calculations also confirm that dangling bonds of clean BN edges merge to give interlayer bonds that make further functionalization much more difficult. The reported reaction pathway should allow for other new functionalizations of pure BN and of the rimmed SiO₂/h‐BN composites.     

Solid-State NMR-Driven Crystal Structure Prediction of Molecular Crystals: The Case of Mebendazole

Among all possible NMR crystallography approaches for crystal-structure determination, crystal structure prediction – NMR crystallography (CSP-NMRX) has recently turned out to be a powerful method. In the latter, the original procedure exploited solid-state NMR (SSNMR) information during the final steps of the prediction. In particular, it used the comparison of computed and experimental chemical shifts for the selection of the correct crystal packing. Still, the prediction procedure, generally carried out with DFT methods, may require important computational resources and be quite time-consuming, especially if there are no available constraints to use at the initial stage. Herein, the successful application of this combined prediction method, which exploits NMR information also in the input step to reduce the search space of the predictive algorithm, is presented. Herein, this method was applied on mebendazole, which is characterized by desmotropism. The use of SSNMR data as constraints for the selection of the right tautomer and the determination of the number of independent molecules in the unit cell led to a considerably faster process, reducing the number of calculations to be performed. In this way, the crystal packing was successfully predicted for the three known phases of mebendazole. To evaluate the quality of the predicted structures, these were compared to the experimental ones. The crystal structure of phase B of mebendazole, in particular, was determined de novo by powder diffraction and is presented for the first time in this paper.     

Non-classical Velocity Statistics in Counterflow Quantum Turbulence

In this work we analyse the statistical distribution of turbulent superfluid velocity components in a He II counterflow channel, via two-dimensional numerical simulations presented in past studies. The Probability Density Functions (PDFs) of the superfluid velocity components are investigated at lengthscales smaller than the average intervortex spacing, for varying vortex densities and different wall-normal distances. The results obtained confirm the non-classical signature of quantum turbulence already observed in past numerical studies.     

A multi-objective supplier selection framework based on user-preferences

Annals of Operations Research - This paper introduces an interactive framework to guide decision-makers in a multi-criteria supplier selection process. State-of-the-art multi-criteria methods for...     

Asymmetric Alkylation of Cyclic Ketones with Dehydroalanine via H-Bond-Directing Enamine Catalysis: Straightforward Access to Enantiopure Unnatural α-Amino Acids

The growing importance of structurally diverse and functionalized enantiomerically pure unnatural amino acids in the design of drugs, including peptides, has stimulated the development of new synthetic methods. This study reports the challenging direct asymmetric alkylation of cyclic ketones with dehydroalanine derivatives via a conjugate addition reaction for the synthesis of enantiopure ketone-based α-unnatural amino acids. The key to success was the design of a bifunctional primary amine-thiourea catalyst that combines H-bond-directing activation and enamine catalysis. The simultaneous dual activation of the two relatively unreactive partners, confirmed by mass spectrometry studies, results in high reactivity while securing high levels of stereocontrol. A broad substrate scope is accompanied by versatile downstream chemical modifications. The mild reaction conditions and consistently excellent enantioselectivities (>95 % ee in most cases) render this protocol highly practical for the rapid construction of valuable noncanonical enantiopure α-amino-acid building blocks.     

Holomorphic curves in Shimura varieties

We prove a hyperbolic analogue of the Bloch–Ochiai theorem about the Zariski closure of holomorphic curves in abelian varieties. We consider the case of non compact Shimura varieties completing the proof of the result for all Shimura varieties. The statement which we consider here was first formulated and proven by Ullmo and Yafaev for compact Shimura varieties.     

Calcium Phosphate Particles Coated with Humic Substances: A Potential Plant Biostimulant from Circular Economy

Nowadays, the use of biostimulants to reduce agrochemical input is a major trend in agriculture. In this work, we report on calcium phosphate particles (CaP) recovered from the circular economy, combined with natural humic substances (HSs), to produce a plant biostimulant. CaPs were obtained by the thermal treatment of Salmo salar bones and were subsequently functionalized with HSs by soaking in a HS water solution. The obtained materials were characterized, showing that the functionalization with HS did not sort any effect on the bulk physicochemical properties of CaP, with the exception of the surface charge that was found to get more negative. Finally, the effect of the materials on nutrient uptake and translocation in the early stages of development (up to 20 days) of two model species of interest for horticulture, Valerianella locusta and Diplotaxis tenuifolia, was assessed. Both species exhibited a similar tendency to accumulate Ca and P in hypogeal tissues, but showed different reactions to the treatments in terms of translocation to the leaves. CaP and CaP–HS treatments lead to an increase of P accumulation in the leaves of D. tenuifolia, while the treatment with HS was found to increase only the concentration of Ca in V. locusta leaves. A low biostimulating effect on both plants’ growth was observed, and was mainly scribed to the low concentration of HS in the tested materials. In the end, the obtained material showed promising results in virtue of its potential to elicit phosphorous uptake and foliar translocation by plants.     

Press‐Printed Conductive Carbon Black Nanoparticle Films for Molecular Detection at the Microscale

Carbon black nanoparticle (CBNP) press‐transferred film‐based transducers for the molecular detection at the microscale level were proposed for the first time. Current‐sensing atomic force microscopy (CS‐AFM) revealed that the CBNP films were effectively press‐transferred, retaining their good conductivity. A significant correlation between the morphology and the resistance was observed. The highest resistance was localized at the top of the press‐transferred film protrusions, whereas low values are usually obtained at the deep crevices or grooves. The amount of press‐transferred CBNPs is the key parameter to obtain films with improved conductivity, which is in good agreement with the electrochemical response. In addition, the conductivity of such optimum films was not only Ohmic; in fact, tunneling/hopping contributions were observed, as assessed by CS‐AFM. The CBNP films acted as exclusive electrochemical transducers as evidenced by using two classes of molecules, that is, neurotransmitters and environmental organic contaminants. These results revealed the potential of these CBNP press‐transferred films for providing new options in microfluidics and other related micro‐ and nanochemistry applications.     

Probing Metal Ion Complexation of Ligands with Multiple Metal Binding Sites: The Case of Spiropyrans

Among known molecular switches, spiropyrans attract considerable interest because of their reversible responsiveness to external stimuli and the deep conformational and electronic changes that characterize the switching process between the two isomeric forms [spiropyran (SP) and merocyanine (MC)]. Metal coordination is one of the most interesting aspects of spiropyrans for its potential in sensing, catalysis, and medicinal chemistry, but little is known about the details surrounding spiropyran–metal ion binding. We investigated the interplay between an N‐modified 8‐methoxy‐6‐nitrospiropyran (SP‐E), designed to provide appropriate molecular flexibility and a range of competing/collaborative metal binding sites, with Mg²⁺, Cu²⁺ and Zn²⁺, which were chosen for their similar coordination geometry preferences while differing in their hard/soft character. The formed molecular complexes were studied by means of UV/Vis, fluorescence, and NMR spectroscopies and mass spectrometry, and the crystal structure of the SP‐E–Cu complex was also obtained. The results indicate that the Mg²⁺, Zn²⁺ and Cu²⁺ complexes have identical coordination stoichiometry. Furthermore, the Mg²⁺ and Zn²⁺ complexes display fluorescence properties in solution and visible‐light responsiveness. These results provide important spectroscopic and structural information that can serve as a foundation for rational design of spiropyran‐based smart materials for metal sensing and scavenging applications.