Chemical Science:

Comparison of structural dynamics and coherence of d-d and MLCT light-induced spin state trapping

S. Zerdane, L. Wilbraham, M. Cammarata,* O. Iasco, E. Rivière, M.-L. Boillot, I. Ciofini, and E. Collet*

Light Induced Excited Spin State Trapping (LIESST) in FeII spin-crossover systems is a process switching molecules from low (LS, S=0) to high spin (HS, S=2) states. The direct LS-to-HS conversion being forbidden by selection rules, LIESST involves intermediate states such as 1,3MLCT or 1,3T. The intersystem crossing sequence results in a HS state, structurally trapped by metal-ligand bond elongation through the coherent activation and damping of molecular breathing. The ultrafast dynamics of this process was so far investigated in FeN6 ligand field systems, under MLCT excitation. Here we study LIESST in an FeIIN4O2 spin-crossover material of lower symmetry, which allows quite intense and low-energy shifted d-d bands. By combining ab-initio DFT and TD-DFT calculations and fs optical absorption measurements we demonstrate that, compared to MLCT, d-d excitation induces faster LS-to-HS switching and that the shorter intermediates enhance coherent structural dynamics.


Coming soon in Nature Communication:

     Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

H. T. Lemke*, K. S. Kjær, R. Hartsock, T. B. van Driel, M. Chollet, J. M. Glownia, S. Song, D.  Zhu, E. Pace, S. F. Matar, M. M Nielsen, M. Benfatto, K. J. Gaffney, E. Collet, Marco Cammarata*

The description of ultrafast nonadiabaticchemical dynamics during molecular photo-transformations remains challenging because electronic and nuclear structures impact each other and cannot be treated independently. Here we gain new experimental insights, beyond the Born-Oppenheimer approximation, into the light-induced spin-state trapping (LIESST) dynamics of the prototypical [Fe(bpy)3]2+ compound by time-resolved XANES spectroscopy at sub-30-femtosecond resolution and high signal to noise ratio. The electronic decay from the initial optically excited electronic state towards the high spin state is distinguished from the structural trapping dynamics, which launches a coherent oscillating wave packet (265 fs period) clearly identified as molecular breathing. Throughout the structural trapping, the dispersion of the wave packet along the reaction coordinate reveals details of intramolecular vibronic coupling before a slower vibrational energy dissipation to the solution environment. These findings revisiting the LIESST process illustrate how modern time-resolved XANES provides key information to unravel dynamic details of photo-functional molecules.


International Laboratory between France and Japan:

News :

CNRS: http://www.cnrs.fr/inp/spip.php?article4925

Univ. Rennes 1 : https://www.univ-rennes1.fr/actualites/12122016/controle-de-la-matiere-condensee-nouveau-laboratoire-commun-franco-japonais

Univ. Nantes : https://www.univ-nantes.fr/1481641659656/0/fiche___actualite/&RH=INSTITUTIONNEL_FR

Univ. Versailles St Quentin : http://www.uvsq.fr/signature-au-japon-d-un-laboratoire-international-associe-dedie-a-la-matiere-condensee-388123.kjsp

MaMaSELF : https://www.facebook.com/permalink.php?story_fbid=1747524535565112&id=1502405876743647

Tokyo Tech english : http://www.titech.ac.jp/english/news/2017/037227.html

Tokyo Tech Japanese : http://www.titech.ac.jp/news/2017/037150.html


Elastically driven cooperative response of a molecular material impacted by a laser pulse




Order, better, spincross-over

Work it harder, make it better, describe order, our work on spin-crossover (Daft Punk’s summary version!).

Hiroshi Watanabe, Koichiro Tanaka, Nicolas Bréfuel, Hervé Cailleau, Jean-Franǫis Letard, Sylvain Ravy, Pierre Fertey, Masamichi Nishino, Seiji Miyashita, and Eric Collet
Ordering phenomena of high-spin/low-spin states in stepwise spin-crossover materials described by the ANNNI model
Physical Review B 93 014419 (2016)



Single Laser Shot Spin State Switching of {FeII(pz)[Pt(CN)4]}

Inside Thermal Hysteresis Studied by X-ray Diffraction

Watch the video here:


Author(s): E. Collet, L. Henry, L. Pineiro-Lopez, L. Toupet and J A Real.

Current Inorganic Chemistry, Volume 6 (2016)

We study by x-ray diffraction and optical microscopy the photoswitching, initiated by a single ns laser pulse, of the spin-crossover {FeII(pz)[Pt(CN)4]} material inside its thermal hysteresis. The single-crystal study shows that a complete conversion from low spin to high spin states can be reached with a single laser shot. Partial conversions obtained with weaker laser energy gives rise to HS domains. Our results indicate that the non-linear response to light excitation is mainly driven by the temperature jump of the crystal following laser excitation.



Open access paper in Strucutral Dynamics:

A. Marino, M. Cammarata, S.F. Matar, J.-F. Létard, G. Chastanet, H. T. Lemke, E. Collet*

Activation of coherent lattice phonon following ultrafast molecular spin-state photo-switching: a molecule-to-lattice energy transfer     

Structural Dynamics 3, 023605 (2016) http://dx.doi.org/10.1063/1.4936290


Constructing a France-Japan international lab:

First France-Japan workshop on Impacting materials with light and electric fields and watching real time dynamics (IM-LED 2015) in Tokyo, Japan (November 26th–27th, 2015)

 The last news...

Hot paper:

Graphical abstract: Femtosecond spin-state photo-switching dynamics in an FeIII spin crossover solid accompanied by coherent structural vibrations

Ultrafast LIESST dynamics in a FeIII SCO solid accompanied by coherent structural vibrations

R. Bertoni, M. Lorenc, J. Laisney, A. Tissot, M. L. Boillot, S. Matar, E. Collet*
J. Mat. Chem. C, 3 7792 (2015)  DOI: 10.1039/C5TC00854A
Selected as
2015 Journal of Materials Chemistry C Hot Papers

Photo-switching pathway is not a straight line

Sequential activation of molecular breathing and bending during spin-crossover photoswitching revealed with femtosecond optical and x-ray absorption spectroscopy

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.

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*.
Physical Review Letters 113, 227402 (2014).

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

Photoswitching in spin triads nitroxide-copper(II)-nitroxide

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.


VIP: LIESST and reverse LIESST in a spin-crossover solid

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)

2014 International Year of Crystallography

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.

Lundi 20 Janvier : émission radio "Autour de la question: qu’est-ce que la cristallographie" de Caroline Lachowsky sur RFI

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.

Molecular motion watched

Bradley Siwick, Eric Collet Nature, 496, 306 (2013)

Switching with light from 4D to 3D periodicity: aperiodic spin-state ordering revealed and erased by light (Physical Review Letters)

Aperiodic spin state ordering of bi-stable molecules and its photoinduced erasing

We describe a novel type of ordering phenomenon associated with the incommensurate occupational modulation of bistable molecular magnetic states. This unusual type of aperiodicity resulting from the ordering of multi-stable electronic states opens new possibilities for addressing such materials by light. Here we show that light can switch the crystal from 4D to 3D periodic structure. Mixing aperiodicity, multi-stability and photoinduced phenomena opens new perspectives for directing complex order and function in material science.
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)

Hot paper in Angewandte Chemie: Ultrafast magnetic switching in ultrasmall crystals

Our paper is selected as Hot paper in Angewandte Chemie.

Femtosecond spin-state photo-switching of molecular nanocrystals evidenced by optical spectroscopy

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. Collet

Angew. Chem. Int. Ed., 51, 7485-7489 (2012)

Our first experiment at the X-FEL LCLS !!!

Our proposal for experiment at the X-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

More information here.

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.

Phys. Chem. Chem. Phys., 14, 6192-6199 (2012).

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.

Cascading photoinduced, elastic, and thermal switching of spin states

triggered by a femtosecond laser pulse in an Fe(III) molecular crystal

M. Lorenc, Ch. Balde, W. Kaszub, A. Tissot, N. Moisan, M. Servol, M. Buron-Le Cointe, H. Cailleau, P. Chasle, P. Czarnecki, M. L. Boillot, and E. Collet

Phys. Rev. B, 85, 054302 (2012)

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.


Probing Charge-Transfer Excited States in a Quasi Non-Luminescent

Electron-Rich Fe(II)-Acetylide Complex by Femtosecond Optical Spectroscopy

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 Cointe

Chemistry: A European Journal, 18, 2051 – 2055 (2012) DOI: 10.1002/chem.201103048

CLick here for the VIdeo

X-ray diffraction probes in real time changes of the molecular structure induced by a femtosecond laser flash.

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

J. Mater. Chem., 2011, Advance Article  DOI: 10.1039/C1JM14163E

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

Physical Review B, 84, 121102 (2011) DOI: 10.1103/PhysRevB.84.121102

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

Europhysics Letters, 96 17004 (2011)   doi: 10.1209/0295-5075/96/17004

 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.

Capturing One-Dimensional Precursors of a Photoinduced Transformation in a Material

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.

Des molécules magnétisées par un flash laser  Physical Review Letters 103,028301(2010)

Commuter par un flash laser l’état physique d’un matériau, de non magnétique à magnétique, d’isolant à conducteur..., ouvre un nouveau défi dans l’adressage optique de l’information. Cependant, pour aller vers de possibles applications et optimiser les dispositifs, il est nécessaire de comprendre les mécanismes qui se cachent derrière ces phénomènes qui sont encore mal compris. Des chercheurs de l’université de Rennes 1 et du CNRS, en collaboration avec l’ESRF(1) et le Tokyo Institute of Technology, viennent d’observer les processus élémentaires de la commutation de l’état magnétique et optique d’un cristal moléculaire. Les molécules se stabilisent à partir d’une échelle de temps du millionième de millionième de seconde (1 ps). Ces travaux font l’objet d’une publication dans la revue Physical Review Letters(2).

En combinant des mesures ultra-rapides optiques et de diffraction des rayons X permettant de connaître la structure de la matière à l’échelle atomique, ces chercheurs  ont pu observer que l’état électronique excité par la lumière engendre des réorganisations de la structure, de l’échelle de la molécule à celle du matériau. Ces mécanismes sont essentiels pour  stabiliser les nouvelles propriétés physiques générées par la lumière. C’est une nouvelle étape dans le développement de la science structurale ultra-rapide, ou moment où la nouvelle source européenne de rayonnement X-FEL est en construction à Hamburg.


Le changement d’état électronique induit par le flash laser est stabilisé par la réorganisation moléculaire, entrainant les modifications spectaculaires des propriétés optiques (couleur) et magnétiques.

(1) Centre européen de rayonnement synchrotron.

 (2)Lorenc M., Hebert J., Moisan N., Trzop E., Servol M., Buron-Le Cointe M., Cailleau H., Boillot M., Pontecorvo E., Wulff M., Koshihara S., Collet E."Successive Dynamical Steps of Photoinduced Switching of a Molecular Fe(III) Spin-Crossover Material by Time-Resolved X-Ray Diffraction." Physical Review Letters, 103, 028301 (2009)