In chemistry and physics, LIESST (Light-Induced Excited Spin-State Trapping) is a method of changing the electronic spin state of a compound by means of irradiation with light.Phillip Gūtlich, Light Induced Electronic Spin State Trapping (LIESST)
Many

transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...

complexes with

electronic configuration In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon atom ...

d⁴-d⁷ are capable of

spin crossover Spin crossover (SCO) is a phenomenon that occurs in some metal complexes wherein the spin state of the complex changes due to an external stimulus. The stimuli can include temperature or pressure. Spin crossover is sometimes referred to as spin ...

(and d⁸ when molecular symmetry is lower than O_h). Spin crossover refers to where a transition from the high spin (HS) state to the low spin (LS) state or vice versa occurs. Alternatives to LIESST include using thermal changes and pressure to induce spin crossover. The metal most commonly exhibiting spin crossover is iron, with the first known example, an iron(III) tris(dithiocarbamato) complex, reported by Cambi Cambi, L.; Cagnasso, A. Atti. Accad. Naz. Lincei, CI. Sci. Fis., Mat. Nut., Rend. 1931, 13, 809. Cambi, L.: Szego, L. Ber. Drsch. Chem. Ges. B 1931, 64, 259. et al. in 1931. For iron complexes, LIESST involves excitation of the low spin complex with green light to a triplet state. Two successive steps of

intersystem crossing Intersystem crossing (ISC) is an isoenergetic radiationless process involving a transition between the two electronic states with different spin multiplicity. Excited Singlet and Triplet States When an electron in a molecule with a singlet ground ...

result in the high spin complex. Movement from the high spin complex to the low spin complex requires excitation with red light.

References

Laboratory techniques Coordination chemistry {{chem-stub