First glimpse of the soft x-ray induced excited spin-state trapping effect dynamics on spin cross-over molecules

Abstract

The dynamics of the soft x-ray induced excited spin state trapping (SOXIESST) effect of Fe(phen)2(NCS)2 (Fe-phen) powder have been investigated by x-ray absorption spectroscopy (XAS) using the total electron yield method, in a wide temperature range. The low-spin (LS) state is excited into the metastable high-spin (HS) state at a rate that depends on the intensity of the x-ray illumination it receives, and both the temperature and the intensity of the x-ray illumination will affect the maximum HS proportion that is reached. We find that the SOXIESST HS spin state transforms back to the LS state at a rate that is similar to that found for the light induced excited spin state trapping (LIESST) effect. We show that it is possible to use the SOXIESST effect in combination with the LIESST effect to investigate the influence of cooperative behavior on the dynamics of both effects. To investigate the impact of molecular cooperativity, we compare our results on Fe-phen with those obtained for Fe{[Me2Pyrz]3BH}2 (Fe-pyrz) powder, which exhibits a similar thermal transition temperature but with a hysteresis. We find that, while the time constant of the dynamic is identical for both molecules, the SOXIESST effect is less efficient at exciting the HS state in Fe-pyrz than in Fe-phen.

Highly Efficient Thermal and Light-Induced Spin-State Switching of an Fe(II) Complex in Direct Contact with a Solid Surface

“…Below 70 K the HS fraction increases with decreasing temperature, which can be attributed to SOXIESST. 24,25 The temperature at which half of the molecules are in the HS state is T 1/2 = 162(4) K, which is the same within error as for the bulk system. 27 The width of the transition defined as the difference between the temperatures at which 80% of the molecules are in the HS and LS states, respectively, is ΔT 80 = 83(6) K. This is lower than for a submonolayer of [Fe(NCS) 2 L] on HOPG, 17 suggesting a higher uniformity in the intermolecular and moleculeÀsubstrate interactions.…”

“…The measurements were carried out with reduced X-ray photon flux to minimize the effect of soft X-rayinduced excited spin-state trapping (SOXIESST) 24,25 below T = 70 K. Figure 2 shows the temperature-and light-induced spin-state switching of 0.4 ML of [Fe(bpz) 2 phen] on HOPG. Fe L 2,3 XA spectra recorded at room temperature (red line) and T = 6 K (blue line) are distinctly different.…”

Hysteresis and change of transition temperature in thin films of Fe{[Me2Pyrz]3BH}2, a new sublimable spin-crossover molecule

“…Spin-crossover (SCO) molecules have been the object of many studies 1-4 since their discovery by Cambi and Szegö. 5 This category of metal-organic complexes can undergo a spin transition under the influence of external stimuli (temperature, light, [6][7][8][9][10][11] ligand-driven, 12 X-rays, 13,14 pressure, 15 magnetic field, 16 and current and electric field 17 ). The interest in low-dimensional systems based on spin-crossover molecules has recently seen a significant development, 3,6,18,19 driven by potential technical applications as displays, sensors and memories such as memristors, 17 nano-sized cantilevers, and other emerging applications.…”

Engineering On‐Surface Spin Crossover: Spin‐State Switching in a Self‐Assembled Film of Vacuum‐Sublimable Functional Molecule

“…Apart from the thermal SCO, the light‐induced excited spin‐state trapping (LIESST) effect at the nanoscale is of great importance, especially from applications perspective . Since our detection method of SCO in the film sample is XAS, which results in soft X‐ray‐induced excited spin‐state trapping (SOXIESST) at low temperature, the XAS measurements were performed at an intermediate temperature of 100 K to avoid mixing of thermally activated SCO with SOXIESST. Attempts have not been made to observe the visible‐light‐induced LIESST effect in the thin film sample of [Fe(H 2 B(pz) 2 ) 2 (C 12 ‐bpy)].…”