Cryptophanols,new versatile compounds for the synthesis of functionalized cryptophanes and polycryptophanes

After deprotection with a palladium catalyst, mono-allylated cryptophane-A (1, 2) and cryptophane-E (3) gave the new cryptophanols 4, 5 and 6, respectively, which are important key compounds for the preparation of monofunctionalized cryptophanes as well as for the design of large supramolecular hosts such as the bis-cryptophanes 7 and 8.     

Reassigning hydrogen-bond centering in dense ice

Hydrogen bonds in H2O ice change dramatically upon compression. Thereby a hydrogen-bonded molecular crystal, ice VII, is transformed to an atomic crystal, ice X. Car-Parrinello simulations reproduce the features of the x-ray diffraction spectra up to about 170 GPa but allow for analysis in real space. Starting from molecular ice VII with static orientational disorder, dynamical translational disordering occurs first via creation of ionic defects, which results in a systematic violation of the ice rules. As a second step, the transformation to an atomic solid and thus hydrogen-bond centering occurs around 110 GPa at 300 K and no novel phase is found up to at least 170 GPa.     

Photomechanical control of the electronic properties of linear pi-conjugated systems

Photodynamic molecular architectures have been synthesized by covalent fixation of a photoisomerizable dimethylazobenzene group at two fixed points of conformationally flexible pi-conjugated quater- and sexithiophene chains. Theoretical geometry optimization shows, in excellent agreement with crystallographic structures, that the mode of fixation of the azo group plays a determining role in the geometry of the final molecular architecture and on its ability to perform the expected photoinduced molecular motion. Thus, covalent fixation of meta-dimethylazobenzene on a quaterthiophene chain results in a conformationally locked system in which photoisomerization of the azo group is hindered. However, the experimental results of optical, (1)H NMR spectroscopic, and electrochemical investigations show that when an azobenzene group is connected at the para positions of the phenyl rings, trans-to-cis photoisomerization of the azo group induces a conformational transition and dimensional changes in the underlying pi-conjugated oligothiophene chain. These experimental results unequivocally show that the photochemically induced geometrical changes produce in turn an increase in the HOMO level and a narrowing of the HOMO-LUMO gap. This therefore provides the first evidence of photomechanical control of the electronic properties of linear pi-conjugated systems.     

Performance of radar absorbing materials by waveguide measurements for X- and Ku-band frequencies

In this work, samples consisting of an elastomeric matrix containing different kinds of active materials in particulate form were prepared for reflectivity measurements. The materials individually used in weight contents of 80% in polychloroprene matrix were: carbonyl-iron (CI) and doped ferrite powders. The microwave reflectivity levels were determined from the magnetic and dielectric properties of the elastomeric composites obtained from scattering data, by fitting the samples in a waveguide, for measurements in the frequency range from 8 to 16 GHz. Better microwave absorption for X-band was obtained for CI while doped ferrite absorbed at higher frequencies (Ku-band).     

Reversible Guest Uptake/Release by Redox‐Controlled Assembly/Disassembly of a Coordination Cage

Controlling the guest expulsion process from a receptor is of critical importance in various fields. Several coordination cages have been recently designed for this purpose, based on various types of stimuli to induce the guest release. Herein, we report the first example of a redox‐triggered process from a coordination cage. The latter integrates a cavity, the panels of which are based on the extended tetrathiafulvalene unit (exTTF). The unique combination of electronic and conformational features of this framework (i.e. high π‐donating properties and drastic conformational changes upon oxidation) allows the reversible disassembly/reassembly of the redox‐active cavity upon chemical oxidation/reduction, respectively. This cage is able to bind the three‐dimensional B₁₂F₁₂^2? anion in a 1:2 host/guest stoichiometry. The reversible redox‐triggered disassembly of the cage could also be demonstrated in the case of the host–guest complex, offering a new option for guest‐delivering control.     

Synthesis of a thermally stable hybrid acene-thiophene organic semiconductor via a soluble precursor

An acene fused-thiophene hybrid p-semiconductor exhibiting high thermal stability has been synthesized via a soluble precursor bearing sterically interacting trimethylsilyl groups. [structure: see text]     

Air-stable,electron-deficient Fe(II) catalytic porphyrins. Characterization and molecular structures of rare high spin Fe(II) hexacoordinated porphyrins

The synthesis, characterization, and molecular structures of the first air-stable, hexacoordinated high spin Fe(II) porphyrins (1) with axial alcohols are reported (1 = Fe(II) meso-tetrakis(o-dichlorophenyl)-beta-octanitroporphyrin). The structure of 1 with two axial waters is also presented. The very different conformations and metrics observed with the two types of ligands illustrate the acute interplay between ligands, conformations, and spin states in Fe porphyrins.     

A Bioinspired Synthesis of Polyfunctional Indoles

Polyfunctional indoles bearing substituents at C5 and C6 are prevalent in natural products, pharmaceuticals, agrochemicals, and materials. Owing to the remoteness of the C5 and C6 positions, indoles of this family can be difficult to prepare, and often require multistep syntheses. Herein, we describe a concise process that converts simple derivatives of tyrosine into 5,6‐difunctionalized indoles by direct oxidation of C?H, N?H, and O?H bonds. Our work draws inspiration from the biosynthetic polymerization of tyrosine to make melanin pigments, but makes an important departure to provide well‐defined indole heterocycles.     

Molecular engineering of hybrid π-conjugated oligomers combining 3,4-ethylenedioxythiophene (EDOT) and thiophene-S,S-dioxide units

A series of π-conjugated oligomers based on various combinations of thiophene, 3,4-ethylenedioxythiophene (EDOT) and thiophene-S,S-dioxide units have been synthesized. Theoretical calculations, optical and electrochemical data show that the relative positions of EDOT and S,S-dioxide units in the conjugated system exert strong influence on its electronic properties. The insertion of EDOT units inside the conjugated chain with the S,S-dioxide units located at the lateral positions leads to a planar conjugated system presenting moderate band gap. In contrast, substituted S,S-dioxide units located within the backbone produce a torsion of the conjugated chain. However, the twist angle is significantly reduced when the EDOT and S,S-dioxide moieties are separated by unsubstituted thiophene cycles. Introduction of S,S-dioxide unit in the median position of the chain has a stronger effect on the lowering of the LUMO level while insertion of EDOT units at the lateral positions limits the decrease of the HOMO level. Consequently, the corresponding oligomers present the smallest electrochemical gap while electrooxidation leads directly to the dication state through a bi-electronic process.