- LIESST
In chemistry and physics, LIESST (Light Induced Electronic 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) [http://ak-guetlich.chemie.uni-mainz.de/toss/liesst_med.shtml] ] .
Many
transition metal complexes withelectronic configuration d4-d7 are capable of spin crossover (and d8 when molecular symmetry is lower than Oh) [ Phillip Gūtlich, Andreas Hauser, and Harmut Spiering, Thermal and Optical Switching of Iron(II) Complexes,Angew. Chem. Int. Ed. Engl. 1994.33, 2024-2054 ] . 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 result in the high spin complex. Movement from the high spin complex to the low spin complex requires excitation with red light [ Phillip Gūtlich, Light Induced Electronic Spin State Trapping (LIESST) [http://ak-guetlich.chemie.uni-mainz.de/toss/liesst_med.shtml] ] .References
Wikimedia Foundation. 2010.
