Femtosecond photoswitching dynamics and microsecond thermal conversion driven by laser heating in FeIII spin-crossover solids

Abstract

Contents 1 Introduction 2 The different thermal spin crossover of the investigated Fe(III) compounds 3Ultrafast photoswitching 3.1 Results 3.2 Discussion 4Spin-state switching driven by lattice expansion and heating 4.1 Results 4.2 Discussion 4.3 Comparison between strongly and weakly cooperative crystals 5 Conclusion 6 Experimental section Acknowledgements References

Single Laser Shot Spin State Switching of {FeII(pz)[Pt(CN)4]} Inside Thermal Hysteresis Studied by X-ray Diffraction

“…Some reports have demonstrated that the photoexcitation of the LS state inside the thermal hysteresis can generate the HS phase [7,8,9] 4 )]} (pz=pyrazine) compound studied here was evidenced by Bousseksou et al by Raman, optical spectroscopy and magnetic measurements [9][10][11][12]. In crystals, the photoinduced out-of-equilibrium dynamics initiated by a laser pulse involves several steps [13][14][15][16][17][18]. First the LS to HS photoswitching occurs [6,[19][20]: the photoexcited molecules are trapped within less than 200 femtoseconds in the HS potential by the ultrafast activation and damping of the molecular breathing phonon, through a coherent structural reorganization [21][22][23].…”

“…A 10 mJ laser excites the crystal in the pure LS phase at 293 K (point A on the ascending branch of the hysteresis). It warms up the crystal transiently up to ≈ 313 K, where the full HS state is reached (point B) within less than 1 ms [13][14][15][16][17][18]. This is too fast for our standard camera and we could only observe the crystal, with a colour characteristic of the HS state, 20 ms after laser excitation (point C).…”

“…The consecutive volume expansion drives additional conversion to the HS state during the socalled elastic step on nanosecond time scale [16,17]. The crystal heating due to the absorption of the laser pulse finally induces a transient temperature jump, resulting in a thermal population of the HS state on µs time scale [14,15]. SCO hysteresis at thermal equilibrium, or under light excitation at low temperature, is associated with a phase separation mechanism: the growing of HS domains inside a LS lattice.…”

“…The cooperative transformation of SCO materials may be mediated by elastic coupling during the volume expansion occurring on ns timescale [17]. In addition, the laser pulse warms up the crystal and induces a transient temperature jump on the µs-ms time-scale [13][14][15][16][17][18]. It takes few 10 ms to reach the initial temperature imposed by the cold nitrogen stream.…”

Photoinduced reversible spin-state switching of an FeIII complex assisted by a halogen-bonded supramolecular network

“…[4][5][6][7][8] This has been attributed to a smaller elongation of the Fe-ligand distance, relative to that of Fe II , which lead to a short lifetime of the photoinduced metastable state. 4,5,9 To prevent this fast relaxation from a metastable state to the ground state, a severe distortion of the metal coordination environment, in conjunction with the introduction of extensive intermolecular π-π interactions, has been proposed. 5 (6), and 3.731(7) Å, that are 15, 13, and 11 % shorter than the sum of the van der Waals and ionic radii, respectively.…”