A theoretical approach for elastically driven cooperative switching of spin crossover compounds impacted by an ultrashot laser pulse

International audienceIn this paper we use an elastic model in order to study the elastically driven cooperative switching of spin crossover materials after femtosecond laser excitation. In this model, the molecules occupy a triangular lattice in open boundaries systems and are connected by springs. The volume change of a molecule between its two possible spin states, low-spin and high-spin, determines a variation of the spring length and therefore induces elastic interactions between molecules, which propagates throughout the whole sample as elastic distortions. This model is able to reproduce the multi-step out-of-equilibrium response to ultrashort laser excitation and especially the elastically-driven cooperative response. Then this model is developed in order to predict the behaviour of the system as a function of its different physical parameters, such as the magnitude of the elastic constant or the homogeneity of the photoexcitation. The contribution of the reorganisation of the molecular states during elastic steps, leading to clusters of high-spin molecules towards edge or corners is also revealed

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

See and Act : Overview of Light-control of Transformations in the Solid State

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Spin-state photoswitching dynamics investigated by combining ultrafast optical spectroscopy X-ray diffraction

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Directing the Functionality of a Material by Light : Physical Perspectives

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Tracking Photoinduced Switching in the Solid State by X-ray Diffraction

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Directing Functional Molecular Materials by Light Pulse

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Key Concepts for Light Control of the Functionality of a Material

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