Photoinduced phenomena and structural analysis associated with the spin-state switching in the [FeII(DPEA)(NCS)2] complex

International audienceOut-of-equilibrium photoinduced switching from the low-spin to the high-spin state has been investigated on the iron(II) complex [Fe(II)(DPEA)(NCS)2] by both optical reflectivity and magnetic measurements under continuous light irradiation at low temperature. The photoinduced HS state can be observed up to 47 K and the relaxation process has been followed. Structural changes of both the temperature- and the photoinduced spin-state switching have been analyzed in detail by x-ray diffraction indicating no change of symmetry. Short intermolecular contacts and intramolecular deformations associated with the change of molecular spin state have been quantified. Actually a crossover behavior is observed at thermal equilibrium with however a quasiabrupt shape indicating significant cooperative effects. These aspects are compared between the temperature- and photoinduced spin crossovers

Wavelength selective light-induced magnetic effects in the binuclear spin crossover compound {[Fe(bt)(NCS)2]2(bpym)}

International audienceUsing Fourier transform infrared spectroscopy, x-ray diffraction, and magnetic susceptibility measurements under light irradiation, the selective light-induced excited spin state trapping (LIESST) and the reversible-LIESST effect have been evidenced and studied in depth in the binuclear spin crossover compound {[Fe(bt)(NCS)2]2bpym}. In this system, each magnetic site can switch from low spin (LS) to high spin (HS), so that three states exist, namely, the LS-LS, HS-LS, and HS-HS. All these techniques shine a new light on the high phototunability of this system. In addition to the direct photoswitching from the LS-LS to the HS-LS or to the HS-HS state, here we show that photoinduced switching between the excited photoinduced states can be triggered in a reversible way: from HS-LS to HS-HS (irradiation around 800 nm), or reverse from HS-HS to HS-LS (irradiation around 1300 nm). The nature of the intermediate HS-LS state during the thermal and light-induced spin state changes is also discussed by comparing the spectroscopic measurements and the structural analysis. The loss of inversion symmetry in the HS-LS molecular state, where the two magnetic Fe sites are no more equivalent, is not accompanied by any long-range ordering of the noncentrosymmetric molecules in the crystal. Therefore the continuous double-step spin conversion corresponds to a double crossover

Stress‐induced Domain Wall Motion in a Ferroelastic Mn3+ Spin Crossover Complex

Domain wall motion is detected for the first time during the transition to a ferroelastic and spin‐state ordered phase of a spin crossover complex. Single crystal X‐ray diffraction and resonant ultrasonic spectroscopy (RUS) revealed two distinct symmetry‐breaking phase transitions in the mononuclear Mn 3+ compound [Mn(3,5‐diBr‐sal 2 (323))]BPh 4 , 1. The first at 250 K, involves the space group change Cc → Pc and is thermodynamically continuous, while the second, Pc → P1 at 85 K, is discontinuous and related to spin crossover and spin‐state ordering. Stress‐induced domain wall mobility was detected as softening of the phonon modes at the Pc → P1 transition

Multi-step transitions in Metal Organic Frameworks with Confined Guest

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A brief progress report from the chemistry-physics interface: new tools for old problems

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Étude par diffraction des rayons X de changements structuraux au cours de processus chimiques et physiques photoinduits

The main purpose of this Ph. D. thesis is the structural study of photochemical and photophysical transformations in crystals by X-ray diffraction. We studied selected organic compounds undergoing intramolecular photochemical reactions in a solid state. Previously to these studies, there was alack of reports on structuralmonitoring such processes. Moreover, we focused on molecular phototransformations in selected iron complexes, which allowed the observation of wavelength selectivity of the photosteady states. We also monitored out-of-equilibrium dynamics of the ultra-fast photoinduced transformation by time-resolved X-ray diffraction, evidencing three stages: (i) the picosecond change of the molecular state; (ii) the unit-cell volume expansion in several tens of nanoseconds; (iii) the macroscopic thermal effect on the microsecond time scale.L objet principal de cette thèse est l étude par diffraction des rayons X de cristaux présentant deschangements structuraux au cours de transformations photochimiques et photophysiques. D une part, nous avons étudié des composés organiques présentant des réactions photochimiques intramoléculaires àl état solide. Jusqu'à cette étude, peu de résultats avaient été publiés sur le suivi des changements structuraux lors de tels processus. D autre part, nous nous sommes intéressés à la photo-commutation moléculaire dans des complexes du fer, mettant ainsi en évidence la sélectivité, par la longueur d onde, entre états photo-stationnaires. Nous avons aussi pu suivre la dynamique hors équilibre d unetransformation photoinduite ultrarapide par diffraction résolue en temps révélant ainsi 3 étapes: (i)un changement d état moléculaire dès la picoseconde; (ii)unedilatation de la maille vers quelques 10nanosecondes; (iii)unecommutation thermique macroscopique àl échelle de la microseconde.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Magnetoelectric and MIESST Effects in Spin Crossover Materials Exhibiting Symmetry-breaking

International audienceGiant magnetoelectric coupling and magnetic-field-induced spin state trapping (MIESST) were recently reported in spin crossover materials with polar phases. We discuss these phenomena considering the distinct contributions of the change of the molecular spin state, driven by the magnetic field, and the coupled structural symmetry-breaking during the stepwise change of electric polarisation or MIESST

Multiscale dynamics of photoactive systems

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Multiscale dynamics studied with X-rays : from molecular switching to material transformation

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