Evolution of cooperativity in the spin transition of an iron(II) complex on a graphite surface

Abstract

Cooperative effects determine the spin-state bistability of spin-crossover molecules (SCMs). Herein, the ultimate scale limit at which cooperative spin switching becomes effective is investigated in a complex [Fe(H2B(pz)2)2(bipy)] deposited on a highly oriented pyrolytic graphite surface, using x-ray absorption spectroscopy. This system exhibits a complete thermal- and light-induced spin transition at thicknesses ranging from submonolayers to multilayers. On increasing the coverage from 0.35(4) to 10(1) monolayers, the width of the temperature-induced spin transition curve narrows significantly, evidencing the buildup of cooperative effects. While the molecules at the submonolayers exhibit an apparent anticooperative behavior, the multilayers starting from a double-layer exhibit a distinctly cooperative spin switching, with a free-molecule-like behavior indicated at around a monolayer. These observations will serve as useful guidelines in designing SCM-based devices.

Soft X-ray Absorption Spectroscopy Study of Spin Crossover Fe-Compounds: Persistent High Spin Configurations under Soft X-ray Irradiation

“…Earlier studies have suggested that the mechanism of the SOXIESST effect is analogous to that of the LIESST effect [19,21,22,35]; their similarities and differences were discussed by V. Davesne et al [21,27,36]. Namely, the light or X-ray introduction leads to an excitation of the system from the LS ground state configuration to the excited state configurations and it follows that the excited state configurations decay into a metastable spin triplet HS configuration (intersystem crossing).…”

“…For instance, XAS at Fe L 2,3 -edge utilizes the electronic excitation from the 2p core level to the 3d unoccupied state following the X-ray perturbation. Previous Fe L 2,3 -edge XAS studies on a representative SCO molecule, Fe(phen) 2 (NCS) 2 at low and high temperatures, have established a set of spectroscopic fingerprints for the HS and LS states [32][33][34][35].…”

“…Namely, the light or X-ray introduction leads to an excitation of the system from the LS ground state configuration to the excited state configurations and it follows that the excited state configurations decay into a metastable spin triplet HS configuration (intersystem crossing). Then the spin states can remain trapped in this excited HS state, unless the temperature is high enough to overcome the energy barrier between the HS and LS configurations via the thermal fluctuations [19,21,22,35]. However, when X-rays are turned off, the system again favors the LS ground state configuration.…”

Fragmentation and Distortion of Terpyridine-Based Spin-Crossover Complexes on Au(111)

“…[1][2][3][4][5][6][7][8][9][10][11] Considerable effort has been made to prepare such complexes on surfaces, e. g. for electrical contacting. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] To enable physical vapor deposition, which is the most common technique for obtaining high-quality films, compounds with increased thermal stability have been synthesized. However, even for such robust compounds, fragmen-tation issues have been reported.…”

Direct Visualization of Local Spin Transition Behaviors in Thin Molecular Films by Bimodal AFM

“…The surface/interface energy can be therefore viewed as a key parameter, which governs the SCO properties at the nanoscale . Understanding surface/interface phenomena is not only important to elucidate nanoscale SCO behaviors but also opens up possibilities for engineering these nanomaterials . However, thin films and nanostructures usually have nonuniform properties due to defects, grain boundaries, strain distributions, and so forth.…”