Expanded Pyridiniums: Bis‐cyclization of Branched Pyridiniums into Their Fused Polycyclic and Positively Charged Derivatives—Assessing the Impact of Pericondensation on Structural,Electrochemical, Electronic,and Photophysical Features

This study evaluates the impact of the extension of the π‐conjugated system of pyridiniums on their various properties. The molecular scaffold of aryl‐substituted expanded pyridiniums (referred to as branched species) can be photochemically bis‐cyclized into the corresponding fused polycyclic derivatives (referred to as pericondensed species). The representative 1,2,4,6‐tetraphenylpyridinium ( 1^H ) and 1,2,3,5,6‐pentaphenyl‐4‐(p‐tolyl)pyridinium ( 2^Me ) tetra‐ and hexa‐branched pyridiniums are herein compared with their corresponding pericondensed derivatives, the fully fused 9‐phenylbenzo[1,2]quinolizino[3,4,5,6‐def]phenanthridinium ( 1^H f ) and the hitherto unknown hemifused 9‐methyl‐1,2,3‐triphenylbenzo[h]phenanthro[9,10,1‐def]isoquinolinium ( 2^Me f ). Combined solid‐state X‐ray crystallography and solution NMR experiments showed that stacking interactions are barely efficient when the pericondensed pyridiniums are not appropriately substituted. The electrochemical study revealed that the first reduction process of all the expanded pyridiniums occurs at around ?1 V vs. SCE, which indicates that the lowest unoccupied molecular orbital (LUMO) remains essentially localized on the pyridinium core regardless of pericondensation. In contrast, the electronic and photophysical properties are significantly affected on going from branched to pericondensed pyridiniums. Typically, the number of absorption bands increases with extended activity towards the visible region (down to ca. 450 nm in MeCN), whereas emission quantum yields are increased by three orders of magnitude (at ca. 0.25 on average). A relationship is established between the observed differential impact of the pericondensation and the importance of the localized LUMO on the properties considered: predominant for the first reduction process compared with secondary for the optical and photophysical properties.     

Vladimir Sergeevich Anashin

On the occasion of the 60th birthday of Professor Vladimir Sergeevich Anashin, we present a review of his significant scientific research and related activities.     

Numerical investigation of elastic modes of propagation in helical waveguides

Steel multi-wire cables are widely employed in civil engineering. They are usually made of a straight core and one layer of helical wires. In order to detect material degradation, nondestructive evaluation methods based on ultrasonics are one of the most promising techniques. However, their use is complicated by the lack of accurate cable models. As a first step, the goal of this paper is to propose a numerical method for the study of elastic guided waves inside a single helical wire. A finite element (FE) technique is used based on the theory of wave propagation inside periodic structures. This method avoids the tedious writing of equilibrium equations in a curvilinear coordinate system yielding translational invariance along the helix centerline. Besides, no specific programming is needed inside a conventional FE code because it can be implemented as a postprocessing step of stiffness, mass and damping matrices. The convergence and accuracy of the proposed method are assessed by comparing FE results with Pochhammer-Chree solutions for the infinite isotropic cylinder. Dispersion curves for a typical helical waveguide are then obtained. In the low-frequency range, results are validated with a helical Timoshenko beam model. Some significant differences with the cylinder are observed.     

Design and demonstration of a high-energy booster amplifier for a high-repetition rate petawatt class laser system

We have successfully developed a high-energy, high-repetition rate Ti:sapphire laser system that delivers 33 J before compression at 0.1 Hz. The final booster amplifier is based on a 100 mm diameter Ti:sapphire crystal pumped with 72 J of energy in six beams delivered by three frequency-doubled high-repetition rate Nd:glass lasers. This system is, to the best of our knowledge, the first demonstrated petawatt class laser system running at a high repetition rate.     

Nanometrization of Lanthanide‐Based Coordination Polymers

Heteronuclear lanthanide‐based coordination polymers are microcrystalline powders, the luminescence properties of which can be precisely tuned by judicious choice of the rare‐earth ions. In this study, we demonstrate that such materials can also be obtained as stable solutions of nanoparticles in non‐toxic polyols. Bulk powders of the formula [Ln_2?2xLn′_2x(bdc)₃ ? 4 H₂O]_∞ (where H₂bdc denotes 1,4‐benzene‐dicarboxylic acid, 0≤x≤1, and Ln and Ln′ denote lanthanide ions of the series La to Tm plus Y) afford nanoparticles that have been characterized by dynamic light‐scattering (DLS) and transmission electron microscopy (TEM) measurements. Their luminescence properties are similar to those of the bulk materials. Stabilities versus time and versus dilution with another solvent have been studied. This study has revealed that it is possible to tune the size of the nanoparticles. This process offers a reliable means of synthesizing suspensions of nanoparticles with tunable luminescence properties and tunable size distributions in a green solvent (glycerol). The process is also extendable to other coordination polymers and other solvents (ethylene glycol, for example). It constitutes a new route for the facile solubilization of lanthanide‐based coordination polymers.     

Size dependence of the folding of multiply charged sodium cationized polylactides revealed by ion mobility mass spectrometry and molecular modelling

Ion mobility spectrometry coupled with mass spectrometry was used to experimentally determine the three-dimensional structure of multiply charged sodium cationized polylactides (PLA). In particular, the experiments were conducted to evaluate the influence of the charge state and the size on the gas-phase conformation of cationized PLA. The measured collision cross sections were then compared to calculated values obtained by computational chemistry methods. The most striking feature was the experimental and theoretical observation of a breaking point in the quasilinear relationship between the average collision cross sections and the number of monomer units for the triply charged cations. This breaking point was theoretically demonstrated, for the doubly and triply charged cations, to be associated with a significant folding of the polymer chains around the cationizing agents. The occurrence of such breaking points could be exploited to correlate the charge state of the most intense ion series observed upon electrospray ionization with the number-average molecular mass of a polymer.