Jean-François Létard

Bio: Jean-François Létard is an academic researcher from University of Bordeaux. The author has contributed to research in topics: Spin crossover & LIESST. The author has an hindex of 47, co-authored 174 publications receiving 7809 citations. Previous affiliations of Jean-François Létard include University of Valencia & Ludwig Maximilian University of Munich.

Towards spin crossover applications

Abstract: In this chapter we attempt to review the potential for the application of the spin crossover (SCO) phenomenon in various domains, such as molecular electronics, data storage, display devices. It is evident that SCO properties, such as room-temperature working range, chemical stability, low addressing power, short addressing time, full reversibility, are of promising value in the context of the stringent limits necessary in the future development of information technology, due to the unceasing miniaturization of the components. Of course, many requirements must be fulfilled before any use in a genuine device becomes feasible. Some of these are emphasized and discussed here. Additionally, this review reports recent progress in non-linear optics and photomagnetism of SCO materials.

Structural, Magnetic, and Photomagnetic Studies of a Mononuclear Iron(II) Derivative Exhibiting an Exceptionally Abrupt Spin Transition. Light-Induced Thermal Hysteresis Phenomenon.

Abstract: The new spin-crossover compound Fe(PM-BiA)2(NCS)2 with PM-BiA = N-(2-pyridylmethylene)aminobiphenyl has been synthesized. The temperature dependence of χMT (χM = molar magnetic susceptibility and T...

Structural aspects of spin crossover. Example of the [FeIILn(NCS)2] complexes

Abstract: The interplay between the spin crossover and the structural properties of the complexes in the solid state is still under investigation. In particular the following questions may be asked. What are the structural modifications of the metal coordination sphere at the spin crossover? How are the dimensions and the symmetry of the crystallographic unit cell affected by the spin crossover? Conversely, how may structural properties influence the spin crossover behavior? Do intramolecular parameters account for the features of the spin crossover? What are the relevant characteristics of the crystal packing for the cooperativity? Do the above questions have general answers that can be used for all the spin crossover compounds? This contribution tries to give answers to these questions. The discussion is based on a large structural data set provided in the literature for the six-coordinated iron(II) mononuclear complexes of general formula [FeL n (NCS) 2 ]. The effects of temperature, light and pressure on the X-ray diffraction crystal structures are reviewed. The structural modifications due to the spin crossover are first estimated, these include the expansion and the distortion of the FeN 6 octahedron, the isotropic and the anisotropic changes of the unit cell. The influence of the structural properties on the features of the spin crossover is then discussed. For example, intramolecular properties such as Fe-N bond lengths are in general not relevant to account for the spin crossover features. In contrast, hydrogen bonds play a paramount role in the propagation of the spin conversion throughout the crystal lattice.

Photomagnetism of iron(II) spin crossover complexes—the T(LIESST) approach

Abstract: The Light-Induced Excited Spin State Trapping (LIESST) effect, encountered in some Spin-Crossover (SCO) complexes, is of major interest for the design of optical switches. Nevertheless, until now any applications have been prohibited, because the lifetimes of the photomagnetic states are long enough only at low temperatures. Hereby we review the recent progress made by using the T(LIESST) procedure, which consists of systematically measuring the limit temperature above which a photomagnetic effect in a material is erased by warming the material from 10 K at a rate of 0.3 K min−1. This method has been today applied to more than sixty SCO compounds and by comparing the various materials a relation between T(LIESST) and thermal spin transition (T1/2) temperatures has been obtained, i.e.T(LIESST) = T0 − 0.3T1/2. The second section reports part of works done to identify the parameters affecting the T0 factor; that is to find a guideline for the rational design of materials with long-lived photomagnetic lifetimes at working room temperature. Finally, we present the procedure used to simulate a T(LIESST) curve and illustrate it using the examples of a mononuclear SCO complex and of a binuclear SCO system displaying antiferromagnetic interactions.

A guideline to the design of molecular-based materials with long-lived photomagnetic lifetimes.

Abstract: Materials presenting a stable and reversible switch of physical properties in the solid state are of major interest either for fundamental interests or potential industrial applications. In this context, the design of metal complexes showing a light-induced crossover from one spin state to another, leading to a major change of magnetic and optical properties, is probably one of the most appealing challenges. The so-denoted spin-crossover materials undergo, in some cases, a reversible photoswitch between two magnetic states, but, unfortunately, lifetimes of the photomagnetic states for compounds known so far are long enough only at low temperatures; this prohibits any applications. We have measured and collected the temperatures above which the photomagnetic effect disappears for more than sixty spin-crossover compounds. On the basis of this large data base, a correlation between the nature of the coordination sphere of the metal and the photomagnetic lifetime can be drawn. Such correlation allows us to propose here a general guideline for the rational design of materials with long-lived photomagnetic lifetimes. This result clearly opens the way towards room-temperature photonic materials, based on the spin-crossover phenomenon, which will be of great interest for future communication devices.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Structural Changes Accompanying Intramolecular Electron Transfer: Focus on Twisted Intramolecular Charge-Transfer States and Structures

Abstract: 6. Rehybridization of the Acceptor (RICT) 3908 7. Planarization of the Molecule (PICT) 3909 III. Fluorescence Spectroscopy 3909 A. Solvent Effects and the Model Compounds 3909 1. Solvent Effects on the Spectra 3909 2. Steric Effects and Model Compounds 3911 3. Bandwidths 3913 4. Isoemissive Points 3914 B. Dipole Moments 3915 C. Radiative Rates and Transition Moments 3916 1. Quantum Yields and Radiationless Deactivation Processes 3916