Synthesis of poly(oxypropylene)-lithium bis(trifluoromethyl-sulfonylimide) polymer electrolytes. Diffusion study by NMR techniques

High molecular weight polymers have been prepared by ring-opening polymerization of propylene oxide PO using a Vandenberg initiator. Polymer electrolytes based on this polymer and an imide salt LiTFSI have been investigated. We present the results concerning the synthesis of the polymer and the glass transition temperatures evolution of the complexes with respect to salt composition. Diffusion constants of ¹⁹F and ⁷Li nuclei are determined by NMR techniques and a value of the cationic transport number t⁺ = 0.1 is obtained.     

The 15N chemical shifts in mixed NB2Si and NBSi2 environments of Si3B3N7--a theoretical investigation

Nuclear magnetic resonance (NMR) chemical shifts in solids may be calculated by ab initio methods approximating the solid state by molecular clusters. We employed this technique to obtain estimates of (15)N chemical shifts in NB(2)Si and NBSi(2) environments in the solid state. Such nitrogen environments are found in amorphous (Si/B/N-)ceramics which exhibit very interesting features such as high thermal and mechanical stability. We based our calculations on cutouts of hypothetical Si(3)B(3)N(7) crystals suggested by Kroll and Hoffmann [Silicon boron nitrides: hypothetical polymorphs of Si(3)B(3)N(7), Angew. Chem. Int. Ed. 37 (1998) 2527]. Taking the systematic errors of our calculations into account we expect the chemical shifts in NBSi(2) environments around -293+/-5ppm. Chemical shifts in NB(2)Si environments are expected at -272+/-6ppm. The range of the calculated chemical shifts in NBSi(2) environments coincides with experimental chemical shifts in molecular compounds. Experimental chemical shifts of NB(2)Si nitrogen in molecules appear at lower field than our calculated chemical shifts in the solid state.     

Vibronic effects accelerate the intersystem crossing processes of the through-space charge transfer states in the triptycene bridged acridine–triazine donor–acceptor molecule TpAT-tFFO

Quantum chemical studies employing combined density functional and multireference configuration interaction methods suggest five excited electronic states to be involved in the prompt and delayed fluorescence emission of TpAT-tFFO. Three of them, a pair of singlet and triplet charge transfer (CT) states (S₁ and T₁) and a locally excited (LE) triplet state (T₃), can be associated with the (Me → N) conformer, the other two CT-type states (S₂ and T₂) form the lowest excited singlet and triplet states of the (Me → Ph) conformer. The two conformers, which differ in essence by the shearing angle of the face-to-face aligned donor and acceptor moieties, are easily interconverted in the electronic ground state whereas the reorganization energy is substantial in the excited singlet state, thus explaining the two experimentally observed time constants of prompt fluorescence emission. Forward and reverse intersystem crossing between the singlet and triplet CT states is mediated by vibronic spin–orbit interactions involving the LE T₃ state. Low-frequency vibrational modes altering the distance and alignment of the donor and acceptor π-systems tune the S₁ and T₃ states (likewise S₂ and T₃) into and out of resonance. The enhancement of intersystem crossing due to the interplay of vibronic and spin–orbit coupling is considered a general feature of organic through-space charge-transfer thermally activated delayed fluorescence emitters.

DFT/MRCI quantum chemical studies suggest five excited electronic states to be involved in the prompt and delayed fluorescence emission of TpAT-tFFO.     

Synthesis and characterizations of hemiditactic homopolymers derived of poly(3‐allyl‐3‐methylmalic acid): An example of a new class of polymer's ditacticity

A number of works have been focused on the study of polymers microtacticity and the probability of iso‐, syndio‐, and atactic arrangement of monomers such as polypropylene and poly(methacrylic esters) before the 1980s. This type of study was fewer in the last four decades despite the importance of stereochemical knowledge of macromolecules in the biomedical field. NMR analysis was the invaluable tool for the study of stereochemistry. This work detailed the synthesis and the physicochemical and microtacticity characterizations of new semicrystalline and amorphous polyesters, poly(3‐allyl‐3‐methylmalic acid) (PAlMMLA) derivatives which are part of the poly(malic acid) family. This polymer is biodegradable and biocompatible. It can also be chemically modified for a possible combination with bioactive molecules. It can be synthesized from chiral product leading a stereoregular and semicrystalline structure. In the case of a racemic starting product, the obtained macromolecular structure is amorphous. Semi‐crystalline polyester presented a highly diisotactic structure. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2408–2418     

Ultra-Long Lived Luminescent Triplet Excited States in Cyclic (Alkyl)(amino)carbene Complexes of Zn(II) Halides

The high element abundance and d¹⁰ electron configuration make Zn^II-based compounds attractive candidates for the development of novel photoactive molecules. Although a large library of purely fluorescent compounds exists, emission involving triplet excited states is a rare phenomenon for zinc complexes. We have investigated the photophysical and -chemical properties of a series of dimeric and monomeric Zn^II halide complexes bearing a cyclic (alkyl)(amino)carbene (cAAC) as chromophore unit. Specifically, [(cAAC)XZn(μ-X)₂ZnX(cAAC)] (X=Cl ( 1 ), Br ( 2 ), I ( 3 )) and [ZnX₂(cAAC)(NCMe)] (X=Br ( 4 ), I ( 5 )) were isolated and fully characterized, showing intense visible light photoluminescence under UV irradiation at 297 K and fast photo-induced transformation. At 77 K, the compounds exhibit improved stability allowing to record ultra-long lifetimes in the millisecond regime. DFT/MRCI calculations confirm that the emission stems from ³XCT/LE_cAAC states and indicate the phototransformation to be related to asymmetric distortion of the complexes by cAAC ligand rotation. This study enhances our understanding of the excited state properties for future development and application of new classes of Zn^II phosphorescent complexes.     

Asp-Gly based peptides confined at the surface of cationic gemini surfactant aggregates

Cationic gemini surfactants complexed with anionic oligoglycine-aspartate (called gemini peptides hereafter) were synthesized, and their aggregation behaviors were studied. The effects of the hydrophobic chain length (C10-C22) and the length of the oligoglycine (0-4) were investigated, and it was clearly shown by critical micellar concentration, Krafft temperature, and isothermal surface pressure measurements that the hydrophobic effect and interpeptidic interaction influence the aggregation behavior in a cooperative manner. Below their Krafft temperatures, some of them formed both hydro- and organogels with three-dimensional networks and the Fourier transform infrared measurements show the presence of interpeptidic hydrogen bonds.