Anne Léaustic

Dithiazolylethene-based molecular switches for nonlinear optical properties and fluorescence: synthesis, crystal structure and ligating properties

Two photochromic dithiazolylethene-based derivatives (1a and 2a) incorporating a push–pull structural motif D–π–A are synthesized and structurally characterized. The photochemical reactions, which reversibly modify the connection between the electron donor and acceptor, result in simultaneous and effective photo-modulations of their NLO and fluorescent properties. The photo-switchable NLO behaviors are investigated theoretically by performing INDO calculations. The presence of chelating sites in 2a allows the synthesis of various metal complexes: Cu(hfac)2·2a, Mn(hfac)2·2a and Ag(2a)2CF3SO3. Their crystal structures are determined.

Intercalation of polyethers into the MPS3(M = Mn, Cd) host lattice

Polyethylene oxide and polyethylene glycols can be inserted into MPS3 layered materials preintercalated with hydrated metallic cations.

Photochromic and Reductive Electrochemical Switching of a Dithiazolylethene with Large Redox Modulation

A new dipyridylthiazolylethene (1a) and its dicationic analogue (2a), with two N-methylated pyridyl rings, have been synthesized and structurally characterized. Due to the N-methylation of the pyridyl rings, 2 a displays not only very different photochromic properties, but also undergoes a reductive ring-closing reaction to generate its closed-ring isomer 2b. Careful electrochemical studies coupled with EPR spectroscopy show that this reductive ring-closing reaction takes place when 2a is two-electron reduced. DFT calculations suggest that such a ground-state electrocyclization is driven by a very large stabilization of the reduced closed-ring isomer 2b relative to the reduced open-ring isomer 2a. In addition, 2b exhibits two successive and reversible one-electron reductions at half-wave potentials of 0.04 and -0.14 V versus SCE and a redox modulation as large as 1 V is achieved when passing from 2a to 2b.

Photo-controlled release and uptake of Cu(hfac)2 in solution for a binuclear copper complex with a photochromic dithiazolylethene bridging ligand

A photochromic dithiazolylethene was used as bridging ligand to synthesize a series of homometallic binuclear complexes. It was found that the photochromic activity of the bridging ligand was maintained in solution only in the case of the copper binuclear complex. EPR studies revealed not only a weak magnetic coupling between the two copper ions, but also an interesting photo-controlled release and uptake of the Cu(hfac)2 moiety in solution.

Vacancy ordering and host–guest interactions in CdPS3 intercalates: Results from multidimensional solid state NMR

Cadmium hexathiohypodiphosphate (CdPS3) intercalates with potassium and N,N′-dimethylviologen cations have been studied by complementary one- and two-dimensional solid state NMR experiments. The intercalation process results in vacancies in the Cd sublattice, whose detailed distribution is sensitively reflected in both the 31P and the 113Cd spectra of the host material. Advanced 2-D 31P double quantum and spin echo NMR techniques are used to further investigate the connectivity patterns of the 31P atoms represented by the peaks observed. Simple chemical shift considerations strongly indicate that the vacancy distribution is primarily controlled by electrostatic repulsion effects. Thus a model is developed for the local vacancy arrangement that links structural motifs with stoichiometry and the NMR results. In the case of the methylviologen intercalate NMR allows the study of the interaction between the organic guest molecule and the host material. Owing to strong Coulombic interactions, one positively charged end of the molecule is pinned at a minimum distance to the negatively charged Cd vacancy in the layer on the NMR time scale, while the other end is orientationally disordered relative to the layers. This arrangement provides an excellent fit to the experimental intensity distributions in the one- and two-dimensional 31P MAS NMR spectra.

Structural Investigation of the Hydrolysis-Condensation Process of a Modified Titanium Alkoxide.

Titanium isopropoxide was modified with acetylacetone in order to get stable photosensitive colloids via an hydrolysis-condensation process. The various steps of this process were followed by infrared, 1 H and 13 C NMR and X-Ray absorption (XANES and EXAFS). The latter techniques provided some interesting structural data (coordination of titanium, Ti-O and Ti-Ti distances) on the various species, from the precursor to the colloids. A structural model is proposed for each one, with a scheme of the different reactions occuring during the process.

Non — Redox Intercalation into the MPS3 Lamellar Materials: Chemistry and Physical Properties

The MPS3 compounds, where M stands for a metal in the +2 oxidation state,1 form a class of lamellar semiconductors (Figure 1) with the CdCl2 structural type. These materials have already received considerable attention in the past for their ability to insert lithium and act as cathodes in reversible lithium batteries. This redox chemistry will not be adressed here (for a review, see reference 2).

A Multifunctional Photoswitch: 6π Electrocyclization versus ESIPT and Metalation

A terthiazole-based molecular switch associating 6π electrocyclization, excited state intramolecular proton transfer (ESIPT), and strong metal binding capability was prepared. The photochemical and photophysical properties of this molecule and of the corresponding nickel and copper complexes were thoroughly investigated by steady-state and ultrafast absorption spectroscopy and rationalized by DFT/TDDFT calculations. The switch behaves as a biphotochrome with time-dependent photochemical outcome and displays efficient ESIPT-based fluorescence photoswitching. Both photochemical reactions are suppressed by nickel or copper metalation, and the main factors contributing to the quenching of the electrocyclization are discussed.

Light-Controlled Release and Uptake of Zinc Ions in Solution by a Photochromic Terthiazole-Based Ligand

We have synthesized and fully characterized a photochromic zinc complex with a terphenylthiazole-based ligand with a salen-like cavity. The solution stability of the complex was found to be greatly dependent on the state of the photochromic ligand and an interesting photo-triggered release and uptake of zinc ions was found as well as monitored by its fluorescence. The contrasting stability difference of the zinc complex between its two isomeric states was rationalized by DFT calculations.