The last news...
Sequential activation of molecular breathing and bending during spin-crossover photoswitching revealed with femtosecond optical and x-ray absorption spectroscopy
M. Cammarata, R. Bertoni, M. Lorenc, H. Cailleau, S. Di Matteo, C. Mauriac, J.F. Létard, S. Matar, H. Lemke, M. Chollet, S. Ravy, C. Laulhé, E. Collet.
We study the basic mechanisms allowing light to photoswitch at molecular scale a spin-crossover material from low- to high-spin state. Combined femtosecond x-ray absorption performed at LCLS X-FEL and optical spectroscopy reveal that the structural stabilization of the photoinduced HS state results from a two step structural trapping. Molecular breathing vibrations are first activated and rapidly damped as part of the energy is sequentially transferred to molecular bending vibrations. During the photoswitching, the system follows a curved trajectory on the potential energy surface.
Accepted in Physical Review Letters.
Almost instant: It takes less than 50 fs to switch the spin state of a copper-nitroxide-based molecular magnet using light. The timescale of the phenomenon and its mechanism
W. Kaszub, A. Marino, M. Lorenc, E. Collet*, E.G. Bagryanskaya, E.V. Tretyakov, V.I. Ovcharenko, M.V. Fedin
"Ultrafast photoswitching in copper-nitroxide based molecular magnet"Ang. Chem. Int. Ed, (2014)DOI: 10.1002/anie.201403672R1 and 10.1002/ange.201403672R1.
Almost instant: It takes less than 50 fs to switch the spin state of a copper-nitroxide-based molecular magnet using light. The timescale of the phenomenon and its mechanism are investigated by using femtosecond optical spectroscopy. This type of photoswitching is promising for developing ultrafast photo-magneticmaterials.
In collaboration with Andreas Hauser's group we have investigated
« The role of ligand-field states in the ultrafast photophysical cycle of the prototypical iron(II) spin-crossover compound [Fe(ptz)6](BF4)2 »
A. Marino, P. Chakraborty, M. Servol, M. Lorenc, E. Collet & A. Hauser
Selected as Very Important Paper in Angewandte Chemie International Edition (2014)
We discussed about it on the radioand on the web!
L’Année Internationale de la Cristallographie « International Year of Cristallography – IYCr2014 » sera inaugurée lors d’une cérémonie officielle organisée par l’UNESCO et l’IUCr, qui aura lieu au siège de l’UNESCO, les lundi 20 et mardi 21 janvier 2014.
Avec Eric Collet, Yves Botrytis, Guillaume Fiquet
Mercredi 22 Janvier 2014 : conférence satellite, intitulée « Cristallographie, une clé de la connaissance – Crystallography, a key to knowledge » qui se déroulera au siège de l’UNESCO.
Switching with light from 4D to 3D periodicity: aperiodic spin-state ordering revealed and erased by light (Physical Review Letters)
E. Collet, H. Watanabe, N. Bréfuel, L. Palatinus, L. Roudaut, L. Toupet, K. Tanaka, J.-P. Tuchagues, P. Fertey, S. Ravy, B. Toudic, H. Cailleau
Physical Review Letters, 109 (25), 257206 (2012)
Our paper is selected as Hot paper in Angewandte Chemie.
Femtosecond optical pump–probe spectroscopy is used to study the photoswitching dynamics of FeIII spin-crossover nanocrystals. Results indicate that up to 10 % of the molecules can be photoswitched from low-spin to high-spin states within less than one picosecond
R. Bertoni, Maciej Lorenc, Antoine Tissot, Marina Servol, Marie-Laure Boillot and E. ColletX-ray Free Electron Laser LCLS is Stanford was ranked in the top group and we received 3shifts. This first experiment was successful.
A New Kind of Laser
SLAC's two-mile-long linear accelerator (or linac) has begun a new phase of its career, with the creation of the Linac Coherent Light Source (LCLS).
LCLS produces pulses of X-rays more than a billion times brighter than the most powerful existing sources. The ultrafast X-ray pulses are used much like flashes from a high-speed strobe light, enabling scientists to take stop-motion pictures of atoms and molecules in motion, shedding light on the fundamental processes of chemistry, technology, and life itself:
Probing the Ultrasmall, Capturing the Ultrafast
Ultrafast spin-state photoswitching in a crystal and slower consecutive processes investigated by femtosecond optical spectroscopy and picosecond X-ray diffraction
Eric Collet, Nicolas Moisan, Chérif Baldé, Roman Bertoni, Elzbieta Trzop, Claire Laulhé, Maciej Lorenc, Marina Servol, Hervé Cailleau, Antoine Tissot, Marie-Laure Boillot, Timothy Graber, Robert Henning, Philip Coppens and Marylise Buron-Le Cointe.
We report the spin state photo-switching dynamics in two polymorphs of a spin-crossover molecular complex triggered by a femtosecond laser flash, as determined by combining femtosecond optical pump-probe spectroscopy and picosecond X-ray diffraction techniques. Combining both techniques and tracking how the X-ray data correlate with optical signals allows understanding of how electronic and structural degrees of freedom couple and play their role when the switchable molecules interact in the active crystalline medium. The study sheds light on crossing the border between femtochemistry at the molecular scale and femtoswitching at the material scale. This work we performed in our lab, at the APS synchrotron in Argonne (USA) and in collaboration with M.L. Boillot in Orsay and P. Coppens in Buffalo.
Intermolecular control of thermoswitching and photoswitching phenomena
in two spin-crossover polymorphs
M. Buron-Le Cointe, J. Hébert, C. Baldé, N. Moisan, L. Toupet, P. Guionneau, J. F. Létard, E. Freysz, H. Cailleau, and E. Collet
Phys. Rev. B 85 064114 (2012)
We discuss here the important role of inter-molecular coupling for the thermal and lightinduced molecular state switching in the solid state. Investigations were performed on the two crystalline polymorphs of the spin crossover [Fe(PM BiA)2(NCS)2] material. In addition to structural studies at thermal equilibrium, light-induced phenomena were investigated through photo-crystallography, photo-magnetic and dynamical optical measurements. Strong similarities between the thermal-equilibrium and the out-ofequilibrium light-induced transformations are observed in each polymorph: strong cooperative phenomena in one polymorph versus weak cooperative ones in the second polymorph. These different responses of the two crystalline forms of the compound to external perturbations are discussed at the microscopic level in terms of Ising-like model and two-mode description of on-site molecular potentials.
In this paper we put on solid ground the optical time-resolved study of spin-state photoswitching in an Fe(III) compound whose structural dynamics have been recently unveiled. We provide the experimental evidence of complex dynamics, occurring in succession, and spanning ten decades in time. We show that in addition to the ultra-fast photo-induced molecular switching occurring on the sub-picosecond timescale, there exist two additional switching processes significantly affecting the fate of the macroscopic material: one driven by elastic interactions as volume expansion occurs on 10s nanoseconds, and another one associated with heat diffusion and thermal switching taking place on 10s microseconds.
Ciro D'Amico, Maciej Lorenc, Eric Collet, Katy A. Green, Karine Costuas, Olivier Mongin, Mireille Blanchard-Desce, and Frederic Paul
We present here the study of an electron-rich Fe(II) 4-nitrophenylalkynyl complex which possesses a high hyperpolarizability in its singlet ground state and a negative (and presumably much decreased) NLO-activity in its first excited MLCT state(s). Based on an ensemble of spectroscopic and time-resolved measurements we investigate the ultrafast dynamics for deactivation of the initially populated MLCT singlet state(s) of this particular organometallic complex, which are shown to decay into a metastable triplet state. The purported mechanism is rationalized with DFT calculations. We show that this triplet state, which should also exhibit a strongly diminished hyperpolarizability, is fully formed with a very high quantum yield within 15 ps.
100 Picosecond Diffraction Catches Structural Transients of Laser-Pulse Triggered Switching in a Spin-Crossover Crystal
Eric Collet, Maciej Lorenc, Marco Cammarata, Laurent Guérin, Marina Servol, Antoine Tissot, Marie-Laure Boillot, Hervé Cailleau, Marylise Buron-Le CointeChemistry: A European Journal, 18, 2051 – 2055 (2012) DOI: 10.1002/chem.201103048
This is also our first paper with the new team member Marco Cammarata. This paper, just accepted, will appear soon in Chemistry: A European Journal.
The cooperative spin-state transition of an iron(III) compound [FeIII(3-MeO-SalEen)2]PF6:
thermal- vs. ultra-fast photo-switching
Antoine Tissot, Roman Bertoni, Eric Collet, Loic Toupet and Marie-Laure Boillot
The switching properties of the spin-transition solid [FeIII(3-MeO-SalEen)2]PF6, exhibiting a first-order transition, were investigated by using temperature and light as stimulation. The LMCT (ligand-to-metal charge transfer) transitions, detected by single-crystal transmission measurements, were selected for analyzing the photoswitching process of this cooperative solid. Only optical pump-probe experiments could detect photoinduced low-spin to high-spin conversion because of the too short lived excited state. The spin-state transformation induced by the femtosecond laser flash is very fast: electronic excitation corresponding to the low-spin LMCT transition relaxes toward the transient photoexcited high-spin state within 170 ± 50 fs.
Ultrafast spectral weight transfer in RBaCo2O6−δ (R=Sm, Gd, and Tb): A role of electronic correlation in photoinduced phase transition
Y. Okimoto, T. Miyata, M.S. Endo, M. Kurashima, K. Onda, T. Ishikawa, S. Koshihara, M. Lorenc , E. Collet, H. Cailleau, and T. Arima
In the frame of a close collaboration with our Japanese colleagues from Tokyo Institute of Technology, we studied by femtosecond reflection spectroscopy on a series of A-site ordered perovskite-type cobalt oxide RBaCo2O6−δ (R=Sm, Gd, and Tb) crystals, in which the electronic transfer was controlled by R. The transient reflectivity showed an ultrafast change within a time resolution (≈150 fs) at room temperature and the appearance of signals of a hidden state that were different from the high-temperature metallic state. The transferred spectral weight indicates an important role of electronic correlation in the photoexcited state.
Dynamical separation of the coupled order parameters in the relaxation
process from the photo-induced state
H. Watanabe, H. Hirori, S. Mouri, N. Bréfuel, J.P. Tuchagues, E. Collet, K. Tanaka
We have studied the relaxation dynamics from the photo-induced state in the spin crossover complex [FeH2L2-Me](ClO4)2 by magnetic susceptibility and X-ray diffraction measurements. Just after turning off the laser irradiation, the photo-induced high-spin state immediately starts relaxing back to the low-spin state, while the crystal lattice shows a nucleation process. This result shows that the spin state and lattice deformation should be treated as individual parameters in the non-equilibrium phase transition from the photo-induced state.
Laurent Guérin, Johan Hébert, Marylise Buron-Le Cointe, Shin-ichi Adachi, Shin-ya Koshihara, Hervé Cailleau and Eric Collet
Phys. Rev. Lett. 105, 246101 (2010)
We have captured the formation of a train of photo-transformed molecules in a crystal by using synchrotron light, in the frame of a French-Japanese collaboration.
Recently, a new field has emerged within material science, whereby an ultra-short laser pulse is used for directing the macroscopic physical functionality: from insulating to conducting, from non-magnetic to magnetic, from paraelectric to ferroelectric.... The light pulse transforms the material towards another phase of different electronic and/or structural order. However, the elementary processes are not well understood yet, which limits the development of technologies aspiring to light-control. Therefore, observing how material works during the light-induced transformation is a must. In this paper, we could track such a precursor phenomenon. Unlike the photochemical processes in solution, the photoactive molecules embedded in a crystal are no more independent but respond cooperatively, with spectacular efficiency at times, as one photon can transform hundreds of molecules. In the investigated compound we could detect by using ultra-fast x-ray diffuse scattering that absorption of one photon results in transformation of a train of molecules. It is the primary step leading to 3D transformation previously observed, and one which has remained for long a missing piece of the puzzle.
These experiments were performed on
an equipement developed in Japan,
in the frame of an international collaboration.
A femtosecond Laser flash (red) switches a train of molecules (pink), detected by ultra-fast diffuse scattering.