Spin-Crossover Molecular Switches

Spin-crossover (SCO) metal complexes are among the best known classes of molecular bistable systems. Their optical, magnetic, and other physicochemical properties can be reversibly switched by changing the temperature, pressure, or irradiation with light. Although photoswitching in SCO complexes is well documented in the light-induced excited spin state trapping (LIESST) effect discovered in middle eighties, this effect is usually operative at low temperatures T < 50 K. This imposes serious limitations for its application in genuine photodevices.

We develop molecular photoswitches based on SCO metal complexes that overcome the low-temperature limitations of the LIESST effect. To achieve this, we introduce photoactive ligands into SCO complexes in such a way that the photoisomerization of the ligand modifies the ligand field. This light-driven ligand-based modulation induces a spin transition at the coordinated metal ion that can be thus accomplished at room temperature. The reversibility of the photoswitching process can be utilized to design rewritable memories, whereas the addressing of the spin state at the single molecule level may lead to the development of ultrahigh-density memory units.

So far we achieved unprecedented room-temperature photoswitching of SCO iron complexes in solutions, solids, and thin films.



Phenanthroline-Based Molecular Switches for Prospective Chemical Grafting: A Synthetic Strategy and Its Application to Spin-Crossover Complexes.
M. Mörtel, T. Lindner, A. Scheurer, F. W. Heinemann, M. M. Khusniyarov,
Inorg. Chem. 2019, DOI: 10.1021/acs.inorgchem.9b01424. link

Room Temperature Control of Spin States in a Thin Film of a Photochromic Iron(II) Complex.
L. Poggini, M. Milek, G. Londi, A. Naim, G. Poneti, L. Squillantini, A. Magnani, F. Totti, P. Rosa, M. M. Khusniyarov, M. Mannini,
Materials Horizons 2018, 5, 506–513. link

Synthesis, Characterization, and Properties of Iron(II) Spin-Crossover Molecular Photoswitches Functioning at Room Temperature.
M. Mörtel, A. Witt, F. W. Heinemann, S. Bochmann, J. Bachmann, M. M. Khusniyarov,
Inorg. Chem. 2017, 56, 13174–13186. link

How to Switch Spin-Crossover Metal Complexes at Constant Room Temperature. (concept article)
M. M. Khusniyarov,
Chem. Eur. J. 2016, 22, 15178–15191. link

Light-Induced Spin-Crossover. (review)
M. M. Khusniyarov,
Elsevier Reference Module in Chemistry, Molecular Sciences and Chemical Engineering, (Ed.: J. Reedijk). Waltham, MA: Elsevier, 2015. link

Reversible Photoswitching of a Spin-Crossover Molecular Complex in the Solid State at Room Temperature.
B. Rösner, M. Milek, A. Witt, B. Gobaut, P. Torelli, R. H. Fink, M. M. Khusniyarov,
Angew. Chem. Int. Ed. 2015, 54, 12976–12980. link

Spin Crossover Meets Diarylethenes: Efficient Photoswitching of Magnetic Properties in Solution at Room Temperature.
M. Milek, F. W. Heinemann, M. M. Khusniyarov,
Inorg. Chem. 2013, 52, 11585–11592. link