Tetrahedraphene: A Csp3-centered 3D Molecular Nanographene Showing Aggregation-Induced Emission

The bottom-up synthesis of 3D tetrakis(hexa-peri-hexabenzocoronenyl)methane, “tetrahedraphene”, is reported. This molecular nanographene constituted by four hexa-peri-hexabenzocoronene (HBC) units attached to a central sp³ carbon atom, shows a highly symmetric arrangement of the HBC units disposed in the apex of a tetrahedron. The X-ray crystal structure reveals a tetrahedral symmetry of the molecule and the packing in the crystal is achieved mostly by CH⋅⋅⋅π interactions since the interstitial solvent molecules prevent the π⋅⋅⋅π interactions. In solution, tetrahedraphene shows the same electrochemical and photophysical properties as the hexa-^tBu-substituted HBC (^tBu-HBC) molecule. However, upon water addition, it undergoes a fluorescence change in solution and in the precipitated solid, showing an aggregation induced emission (AIE) process, probably derived from the restriction in the rotation and/or vibration of the HBCs. Time-Dependent Density Functional Theory (TDDFT) calculations reveal that upon aggregation, the high energy region of the emission band decreases in intensity, whereas the intensity of the red edge emission signal increases and presents a smoother decay, compared to the non-aggregated molecule. All in all, the excellent correlation between our simulations and the experimental findings allows explaining the colour change observed in the different solutions upon increasing the water fraction.     

Large coupled magnetoresponses in EuNbO2N

We have explored a new strategy to discover materials with large resistive or capacitive responses to magnetic fields by synthesizing EuMO2N (M = Nb, Ta) perovskites that combine ferromagnetic order of S = 7/2 Eu2+ spins with possible off-center distortions of the d0 M5+ cations enhanced by covalent bonding to N. EuNbO2N shows colossal magnetoresistances at low temperatures and a giant magnetocapacitance. However, the latter response originates from a microstructural effect rather than an intrinsic multiferroism.     

Replacing the carbonyl's oxygen with the difluoromethyl group

Aldehydes or ketones were reacted with 2-(trimethylsilyl)-1,3-dithiane (1) and the products reduced to the corresponding dithianes using tetrafluoroboric acid and sodium borohydride. These sulfur containing compounds were reacted with bromine trifluoride under mild conditions (1-2 min, 0 °C) with a net result of replacing the carbonyls' oxygen with the desired difluoromethyl moiety.     

Interfacial interactions and colloid retention under steady flows in a capillary channel

Colloidal interfacial interactions in a capillary channel under different chemical and flow conditions were studied using confocal microscopy. Fluorescent latex microspheres (1.1 microm) were employed as model colloids and the effects of ionic strength and flow conditions on colloidal retention at air-water interface (AWI) and contact line were examined in static and dynamic (flow) experiments. Colloids were preferentially attached to and accumulated at AWI, but their transport with bulk solution was non-negligible. Changing solution ionic strength in the range 1-100 mM had a marginal effect on colloidal accumulation, indicating forces other than electrostatic are involved. Flow through the open channel resembled Poiseuille flow with AWI acting as a non-stress-free boundary, which resulted in near stagnation of AWI and consequently promoted colloid accumulation. Retention on contact line was likely dominated by film-straining and was more significant in flow relative to static experiments due to hydrodynamic driving force. Modeling and dimensionless analysis of the flow behavior in the capillary channel clearly indicate the important role of apparent surface viscosity and surface tension in colloidal interfacial retention at the pore scale, providing insight that could improve understanding of colloid fate and transport in natural unsaturated porous media.     

Test and evaluation of reference-based nonuniformity correction methods for microbolometer infrared detectors

In the paper, reference-based nonuniformity correction methods for microbolometer infrared detectors are discussed and tested. In order to evaluate their effectiveness, a complete readout circuit for amorphous silicon microbolometer focal plane array has been designed. The tests were carried out on a developed stand including several extended blackbodies. Some modification of standard two-point correction algorithm incorporating detectors response at external shutter to compensate offset drift is also proposed. The obtained results are presented.     

From silver nanoparticles to nanostructures through matrix chemistry

Direct in situ reduction of silver ions by a biopolymer such as agar, without any other reducing nor capping agent is shown in this article to lead either to nanoparticles (typically 12(2) nm in an optimized case) or to more complex nanostructures depending on the reaction conditions used. This approach takes advantage of the porous polymer lattice acting as a template and leads to hybrid Ag–Agar materials with long-term synergic stability. Silver acts as an antibacterial agent for agar whereas the biopolymer prevents agglomeration of the inorganic nanoparticles leading to a stable nanocomposite formed by a thermoreversible biopolymer from which silver nanoparticles can eventually be recovered.     

Diophantine geometry over groups IV: An iterative procedure for validation of a sentence

This paper is the fourth in a series on the structure of sets of solutions to systems of equations in a free group, projections of such sets, and the structure of elementary sets defined over a free group. In the fourth paper we present an iterative procedure that validates the correctness of anAE sentence defined over a free group. The terminating procedure presented in this paper is the basis for our analysis of elementary sets defined over a free group presented in the next papers in the series. Partially supported by an Israel Academy of Sciences Fellowship.     

Diverging rabi oscillations in subwavelength photonic lattices

We show that Rabi oscillations between Bloch modes of an optical waveguide array with subwavelength periodicity diverge, both in frequency and in field amplitude, when the optical wavelength approaches a mathematical exceptional point at which the Bloch mode becomes self-orthogonal.