Unilaterally Fluorinated Acenes: Synthesis and Solid‐State Properties

The rapid development of organic electronics is closely related to the availability of molecular materials with specific electronic properties. Here, we introduce a novel synthetic route enabling a unilateral functionalization of acenes along their long side, which is demonstrated by the synthesis of 1,2,10,11,12,14‐hexafluoropentacene ( 1 ) and the related 1,2,9,10,11‐pentafluorotetracene ( 2 ). Quantum chemical DFT calculations in combination with optical and X‐ray absorption spectroscopy data indicate that the single‐molecule properties of 1 are a connecting link between the organic semiconductor model systems pentacene (PEN) and perfluoropentacene (PFP). In contrast, the crystal structure analysis reveals a different packing motif than for the parent molecules. This can be related to distinct F???H interactions identified in the corresponding Hirshfeld surface analysis and also affects solid‐state properties such as the exciton binding energy and the sublimation enthalpy.     

Bubbles and collapses: Fire phenomena of flame‐retarded flexible polyurethane foams

Flexible polyurethane foams (FPUF) are easy to ignite and exhibit rapid flame spread. In this paper, the fire phenomena of two standard foam formulations containing tris(1,3‐dichloro‐2‐propyl) phosphate (FR‐2) and a halogen‐freepoly (ethyl ethylene phosphate) (PNX), respectively, as flame retardants are compared. A multi‐methodological approach is proposed which combines standard fire tests as well as new investigatory approaches. The thermophysical properties of the foams were determined by thermogravimetric analysis (TG), reaction to small flames was studied by means of the limiting oxygen index (LOI) and UL 94 HBF test, and the burning behavior was investigated with the cone calorimeter. Further, temperature development in burning cone calorimeter samples was monitored using thermocouples, and rheological measurements were performed on pyrolyzed material, delivering insight into the dripping behavior of the foams. This paper gives comprehensive insight into the fire phenomena of flame‐retarded FPUFs that are driven by the two‐step decomposition behavior of the foams. LOI and UL 94 HBF tests showed a reduced flammability and reduced tendency to drip for the flame‐retarded foams. TG and cone calorimeter measurements revealed that the two‐step decomposition behavior causes two stages during combustion, namely structural collapse and pool fire. The flame‐retardant mode of action was identified to take place primarily during the foam collapse and be based mainly on flame inhibition. However, some condensed‐phase action was been measured, leading to significantly increased melt viscosity and improved dripping behavior for foams containing PNX.     

Intramolecular C(sp3)–H Bond Oxygenation by Transition-Metal Acylnitrenoids

This study demonstrates for the first time that easily accessible transition-metal acylnitrenoids can be used for controlled direct C(sp³)-H oxygenations. Specifically, a ruthenium catalyst activates N-benzoyloxycarbamates as nitrene precursors towards regioselective intramolecular C−H oxygenations to provide cyclic carbonates, hydroxylated carbamates, or 1,2-diols. The method can be applied to the chemoselective C−H oxygenation of benzylic, allylic, and propargylic C(sp³)−H bonds. The reaction can be performed in an enantioselective fashion and switched in a catalyst-controlled fashion between C−H oxygenation and C−H amination. This work provides a new reaction mode for the regiocontrolled and stereocontrolled conversion of C(sp³)-H into C(sp³)−O bonds.     

Photoelectron spectroscopy of electronic surface structure of the Cs/GaN and Cs/InN interfaces

The electronic structure of the epitaxial GaN, InN nanolayers, and the ultrathin Cs/GaN and Cs/InN interfaces was investigated under ultrahigh vacuum at various Cs coverages. The experiment was carried out using synchrotron-based photoelectron spectroscopy. The photoemission spectra of the valence band and the In 4d, N 2s, Ga 3d, and Cs 4d semicore levels were studied as a function of Cs coverages. It was found that the Cs adsorption in the submonolayer coverage region causes substantial changes in the spectra due to charge transfer between the Cs adlayer and surface Ga or In atoms. The strong interaction of the dangling bonds of Ga or In with Cs adatoms effectively increases the Ga or In valency.     

Influence of the size and the attached organic tail of modified detonation nanodiamond on the physical properties of liquid crystals

For the functionalisation of the detonation nanodiamond (DND), we attached via grafting carboxylate groups, leading to only one of such groups per 5000–6000 carbon units. Activation of the COOH-surface functionalised groups allowed the attachment of various organic tails. Dielectric and electro-optical properties of nematic liquid crystalline mixtures (LCMs) doped with modified DND (MDND) have been investigated. It is established that the effect of MDND on the dielectric properties of the LCMs depends on the size of the nanoparticles and the type of rod-like elongated organic molecules attached to the MDND. It was found that nanoparticles of small size (4–5 nm) do not significantly affect the parameters of LCMs. At the same time, the conglomerates based on MDND of about 50 nm or about 100 nm in diameter can increase or decrease the dielectric anisotropy and the response time of LCMs to about 1.5–2.5 times, depending on the polarity of the tails.     

Silica-coated Au/Ag nanorods with tunable surface plasmon bands for nanoplasmonics with single particles

We present the synthesis and analysis of silica-coated Au/Ag bimetallic nanorods with controlled surface plasmon bands. Depending on the thickness of Ag shell deposited on the Au nanorod surface, there is a blue-shift on the longitudinal surface plasmon band of Au nanorods, which can be expressed by an approximate formula derived from the absorption profile of light in Ag films using finite difference time domain simulations. The subsequent coating of silica shell not only enhances the stability of the Au/Ag bimetallic nanorods but also provides a mesoporous host for optically active species. Minute red-shifts of the longitudinal resonance mode, induced by stepwise increased silica shell volumes, are shown. Application as carrier for fluorescent rhodamine B molecules is demonstrated by photoluminescence analysis. On the single-particle level, dark field microscopy of Au/Ag-silica nanorods was finally employed. This introduces a route towards revealing the relation between structure, shape, and optical (plasmonic) properties of complex composite metal particles as well as fabrication strategies for nanoassemblies of tailored structures in the field of nanoplasmonics.     

Antiferroelectric alignment and mechanical director rotation in a hydrogen-bonded chiral SmC* A elastomer

A new type of chiral smectic elastomer based on poly[4-(6-acryloyloxyhexyloxy)benzoic acid] is discussed. The layer structure and the molecular tilt stabilized by hydrogen bonding between side groups are identified by X-ray measurements. Well aligned and optically clear monodomain samples with smectic layers in the film plane are obtained by uniaxial stretching and then frozen-in by additional gamma-radiation crosslinking. In this monodomain state, two opposite orientations of director tilt are distributed through the sample thickness and alternate between neighbouring layers in a zigzag fashion. This structure of the stress-aligned chiral smectic C elastomer is similar to that of antiferroelectric liquid crystals of the smectic C^* _A type. Further mechanical stretching in the layer plane induces a gradual c-director reorientation along the new stress axis, when a threshold deformation ~ 20% is exceeded. The (reversible) transition proceeds as a director azimuthal rotation around the smectic C cone, with the layers essentially undistorted and the tilt angle of the side mesogenic groups preserved.     

Development of an Enzyme-Linked Immunosorbent Assay (ELISA) for the Herbicide Propanil

Although the extensively used postemergence herbicide propanil itself is of low acute toxicity in mammals, it raises environmental concerns due to its effect on aquatic organisms and other adverse impacts. Therefore, in order to obtain a rapid analytical method for this pesticide, an indirect enzyme-linked immunosorbent assay (ELISA) has been developed. Antibodies obtained against a conjugate of 3,4-dichloroaniline coupled to succinylated proteins were tested in hapten-homologous and heterologous indirect ELISA formats using various N -(dichlorophenyl)-succinamic acid derivatives conjugated to carrier proteins as coating antigens. Titers in ELISA were found to be significantly affected by the type and quantity of coating antigen. One of the optimized systems using N -(2,4-dichlorophenyl)-succinamic acid and N -(3,5-dichlorophenyl)-succinamic acid conjugated to ovalbumin allowed serum dilution of 1 : 10,000 and IC 50 values of 2.2 and 2.7 ng/mL for propanil, respectively. The limit of detection (LOD) of the immunoassays is 0.2 ng/mL. Other optimized ELISA systems based on different dichloroaniline-based coating antigens also offered similar sensitivities. The ELISA systems appeared to tolerate methanol and ethanol upto 5% concentration. For confirmatory purposes, the ELISA protocol was compared with a highly sensitive gas chromatographic method coupled with mass spectrometric detection (GC-MS). Spiked propanil content was detected both by ELISA and GC-MS in methanolic rice extract. Detection sensitivities of the two analytical systems appeared to closely correlate with each other in the range of 10-90 ng/mL (0.02-0.18 µg/g), indicating the utility of the immunoanalytical method in detecting propanil content in rice, the main commodity propanil is being applied on.     

The Effect of Substituents on the Reactivity of the Double Bond of D-Glycals

Abstract

A study was made concerning the effect of substituants at 0-3, 0-4 and 0-6 of d-galactal and d-glucal (1, 5-anhydro-2-deoxy-d-lyxo- and -d-arabino-hex-1-enitol, respectively) on the double bond reactivity in the chloroazide addition reaction. Results from the quantum chemical calculations of the model structures (ab initio) and also of the whole cyclic molecules in the half-chair conformation (MINDO-3) together with the reaction indices of olefin carbon atoms are presented. These studies snow that (1) the double bond reactivity and the chloroazide addition mechanism are only affected by the substituent at 0-3; (2) the influence of the acyl group is only due to its inductive effect; (3) no interaction between the acyl and the olefin fragments through space was detected. Three 0-acetyl-di-0-benzyl-d-galactals were synthesized.