Twisting of Porphyrin by Assembly in a Metal-Organic Framework yielding Chiral Photoconducting Films for Circularly-Polarized-Light Detection

While materials based on organic molecules usually have either superior optoelectronic or superior chiral properties, the combination of both is scarce. Here, a crystalline chiroptical film based on porphyrin with homochiral side groups is presented. While the dissolved molecule has a planar, thus, achiral porphyrin core, upon assembly in a metal–organic framework (MOF) film, the porphyrin core is twisted and chiral. The close packing and the crystalline order of the porphyrin cores in the MOF film also results in excellent optoelectronic properties. By exciting the Soret band of porphyrin, efficient photoconduction with a high On-Off-ratio is realized. More important, handedness-dependent circularly-polarized-light photoconduction with a dissymmetry factor g of 4.3×10⁻⁴ is obtained. We foresee the combination of such assembly-induced chirality with the rich porphyrin chemistry will enable a plethora of organic materials with exceptional chiral and optoelectronic properties.     

Modular Synthesis of trans-A2B2-Porphyrins with Terminal Esters: Systematically Extending the Scope of Linear Linkers for Porphyrin-Based MOFs

Differently functionalized porphyrin linkers represent the key compounds for the syntheses of new porphyrin-based metal–organic frameworks (MOFs), which have gathered great interest within the last two decades. Herein we report the synthesis of a large range of 5,15-bis(4-ethoxycarbonylphenyl)porphyrin derivatives, through Suzuki and Sonogashira cross-coupling reactions of an easily accessible corresponding meso-dibrominated trans-A₂B₂-porphyrin with commercially available boronic acids or terminal alkynes. The resulting porphyrins were fully characterized through NMR, MS, and IR spectroscopy and systematically investigated through UV/Vis absorption. Finally, selected structures were saponified to the corresponding carboxylic acids and subsequently proven to be suitable for the synthesis of surface-anchored MOF thin films.     

Wavelength‐Gated Dynamic Covalent Chemistry

Chemical reactions are classically controlled by the judicious choice of functional groups as well as external factors such as temperature and catalysts. However, the use of light‐induced reactions not only offers precise temporal and spatial control, but critically allows highly specific reaction channels to be selectively addressed through wavelength and intensity, thereby enabling targeted covalent bonds to be made and broken. Photoreversible cycloadditions are the most promising candidates to seize the outlined potential upon selective cyclization and cycloreversion, but are today still far from fulfilling these expectations. The current Minireview critically explores the current challenges in the application of photoreversible cycloadditions and discusses the steps necessary to realize their potential in molecular biology, biomimetic systems, 3D laser lithographic processes, and advanced soft matter materials with reprogrammable and self‐healing properties.     

Synthesis,crystal structures and fluorescence properties of two new di- and polynuclear Cd(II) complexes with N2O donor set of a tridentate Schiff base ligand

Two new Cd(II) complexes, having one binuclear structure [Cd₂(L)₂(Cl)₂] (1) and another azido bridged one-dimensional zig-zag polynuclear network [Cd₃(μ_1,1-N₃)₄(L)₂{H₂N(CH₂)₂N(C₂H₅)₂} · H₂O]_n (2) have been synthesized from a tridentate N₂O donor Schiff base ligand LH, [LH = (OCH₃)(OH)C₆H₃CHN(CH₂)₂N(C₂H₅)₂], which is the condensation product of 2-hydroxy-4-methoxybenzaldehyde and 2-diethylaminoethylamine. Both the complexes 1 and 2 have been characterized by elemental analyses, IR & ¹H NMR spectroscopy, TGA and fluorescence studies. Finally their structures have been established by single crystal X-ray diffraction method. Structural study reveals that in the complex 1, two Cd(II) centers are held together by two μ₂-phenolato oxygen atoms and the terminal chlorine atom occupies the apical site of the square pyramidal environment of each metal center. In case of complex 2, the trinuclear asymmetric unit contains octahedral Cd(II) centers which are further held together by doubly end-on azido bridging to form a zig-zag polynuclear structure. It also displays intraligand ¹(π–π^∗) fluorescence and can potentially serve as photoactive material.     

Structurally and conformationally defined small methyl polysilanes

Possessing the property of sigma-bond electron delocalisation, polysilanes are a class of compounds with unique properties. In recent years major progress has been achieved in the theoretical understanding and the synthesis of polysilanes. Much insight into the connection between conformation and electronic properties has been gained from studies of defined small polysilane molecules. The transition from Wurtz type coupling reactions to the stepwise construction of polysilane molecules employing silyl anions as key intermediates has permitted access to defined compounds with a higher degree of structural complexity. Besides this, several methods have been developed to control the conformational properties and thus gain control over the electronic properties of polysilanes.     

Disentangling the physical contributions to the electrical resistance in magnetic domain walls: a multiscale study

We analyze the origin of the electrical resistance arising in domain walls of perpendicularly magnetized materials by considering a superposition of anisotropic magnetoresistance and the resistance implied by the magnetization chirality. The domain wall profiles of L1(0)-FePd and L1(0)-FePt are determined by micromagnetic simulations based on which we perform first-principles calculations to quantify electron transport through the core and closure region of the walls. The wall resistance, being twice as high in L1(0)-FePd than in L1(0)-FePt, is found to be clearly dominated in both cases by a high gradient of magnetization rotation, which agrees well with experimental observations.     

Concerning the Conformation of Isolated Benzylideneaniline

From PE.-spectroscopical studies the torsional angle φ of the N-phenyl ring in isolated benzylideneaniline 1 has been found to be definitely smaller than φ= 90°. An approximate valueφ= 36°has been estimated which is even smaller than the one observed in the crystal (φ= 55°) and suggested to prevail also in solutions of 1 . A reevaluation of the gas phase optical spectrum of isolated 1 supports a torsional angle similar to that found in the other phases. Calculations of the most stable conformation of 1 as well as of stilbene and azobenzene by the MINDO/3-technique lead to torsional angles φ= 90° for both phenyl rings in all cases. These results are at variance with the experimental results and suggest that MINDO/3-like its less advanced precursor MINDO/2 or like CNDO/2–is unreliable for low energy processes involving rotation of π-systems connected by essential single bonds. It is concluded that the π-energy of benzylideneaniline, like that of stilbene or azobenzene, would favor a planar conformation. The increased torsional angle in 1 as compared to the other two iso-conjugate systems arises from a larger steric interaction between phenyl- and bridgeprotons.