Design and Synthesis of Aviram–Ratner‐Type Dyads and Rectification Studies in Langmuir–Blodgett (LB) Films

The design and synthesis of Aviram–Ratner‐type molecular rectifiers, featuring an anilino‐substituted extended tetracyanoquinodimethane (exTCNQ) acceptor, covalently linked by the σ‐spacer bicyclo[2.2.2]octane (BCO) to a tetrathiafulvalene (TTF) donor moiety, are described. The rigid BCO spacer keeps the TTF donor and exTCNQ acceptor moieties apart, as demonstrated by X‐ray analysis. The photophysical properties of the TTF‐BCO‐exTCNQ dyads were investigated by UV/Vis and EPR spectroscopy, electrochemical studies, and theoretical calculations. Langmuir–Blodgett films were prepared and used in the fabrication and electrical studies of junction devices. One dyad showed the asymmetric current–voltage (I–V) curve characteristic for rectification, unlike control compounds containing the TTF unit but not the exTCNQ moiety or comprising the exTCNQ acceptor moiety but lacking the donor TTF part, which both gave symmetric I–V curves. The direction of the observed rectification indicated that the preferred electron current flows from the exTCNQ acceptor to the TTF donor.     

Four bromo‐substituted pyrazoline and isoxazolinone spiro derivatives

Conformational analyses and a structural comparison of the four spiro compounds 3‐bromo‐1,9‐di­phenyl‐4‐p‐tolyl‐7‐oxa‐1,2,8‐tri­aza­spiro­[4.4]­nona‐2,8‐dien‐6‐one, (I), C₂₄H₁₈BrN₃O₂, 3‐bromo‐4‐(4‐methoxy­phenyl)‐1,9‐di­phenyl‐7‐oxa‐1,2,8‐tri­aza­spiro­[4.4]­nona‐2,8‐dien‐6‐one, (II), C₂₄H₁₈BrN₃O₃, 3‐bromo‐4‐(4‐chloro­phenyl)‐1,7,9‐tri­phenyl‐1,2,7,8‐tetra­aza­spiro­[4.4]­nona‐2,8‐dien‐6‐one, (III), C₂₉H₂₀BrClN₄O, and 3‐bromo‐1,7,9‐tri­phenyl‐4‐p‐tolyl‐1,2,7,8‐tetra­aza­spiro­[4.4]­nona‐2,8‐di­en‐6‐one, (IV), C₃₀H_22.89Br_1.11N₄O, are presented. The mol­ecular structures are rather similar, which is as expected since the compounds are all products of concerted 1,3‐dipolar attack on (Z)‐4‐aryl­idene oxazolone and pyrazolone derivatives. The observed conformations tend to favour extended π conjugation of the benzene rings and other π systems, as shown by a comparison of selected geometric parameters of the four structures.     

Attitude dynamic singularities in 3D free-flying manipulators for improved path planning

This paper extends the solution, already presented to the trajectory planning problem of 2D free-flying manipulators, to 3D manipulators. It demonstrates it is possible to design a robotic arm with a special dynamic singularity (attitude singular configuration), thus permitting to determine and execute its trajectory without affecting the attitude of the spacecraft carrying it. This methodology provides an exact solution to trajectory planning problems that are usually dealt with by approximate algorithms based on the concept of Disturbance Map. After a theoretical introduction, some educational design examples are presented.     

Gold nanoparticles stabilized by modified halloysite nanotubes for catalytic applications

A highly sustainable prototype of a flow system based on gold nanoparticles (4.2 nm) supported on thiol‐functionalized halloysite nanotubes (HNTs) was developed for catalytic applications. The catalytic performances were evaluated using the reduction of 4‐nitrophenol to 4‐aminophenol as a model system. Under the best experimental conditions (0.0001 mol%, 1.97 × 10^?8 mg of Au nanoparticles), an impressive apparent turnover frequency value up to 2 204 530 h^?1 was achieved and the halloysite‐based catalyst showed full recyclability even after ten cycles. The high catalytic activity confirms the importance of the use of HNTs as support for Au nanoparticles that can exert a synergistic effect both as medium for transfer of electrons from borohydride ions to 4‐nitrophenol and by modulating interfacial electron transfer dynamics. With the application of flow technology, the obtained heterogeneous HNT@Au catalyst was fully recovered and reused for at least one month.     

Synthesis and X-ray crystal structures of some isothiosemicarbazone complexes

Transition Metal Chemistry - Four complexes of a new isothiosemicarbazone ligand have been prepared and characterized as μ2-pip-(NiL)2 (1), MnL2 (2), UO2L(BrSal)BuOH (3) and (μ2-MoO2L)2...     

Diradical Organic One-Dimensional Polymers Synthesized on a Metallic Surface

We report on the synthesis and characterization of atomically precise one-dimensional diradical peripentacene polymers on a Au(111) surface. By means of high-resolution scanning probe microscopy complemented by theoretical simulations, we provide evidence of their magnetic properties, which arise from the presence of two unpaired spins at their termini. Additionally, we probe a transition of their magnetic properties related to the length of the polymer. Peripentacene dimers exhibit an antiferromagnetic (S=0) singlet ground state. They are characterized by singlet–triplet spin-flip inelastic excitations with an effective exchange coupling (J_eff) of 2.5 meV, whereas trimers and longer peripentacene polymers reveal a paramagnetic nature and feature Kondo fingerprints at each terminus due to the unpaired spin. Our work provides access to the precise fabrication of polymers featuring diradical character which are potentially useful in carbon-based optoelectronics and spintronics.