Light‐Induced Excited Spin State Trapping

This chapter offers reader an opportunity to become familiar with the contemporary view on the principles of spin crossover (SCO) with emphasis on its specific branch, the light-induced excited spin state trapping (LIESST) effect. It surveys the very basic physical models, which can be considered as standard working tools for simple quantitative characterization of finite-temperature behaviour of SCO or LIESST systems. It highlights the importance of structural changes arising upon the light irradiation, as well as the comparison of structural diversity between the thermally and photoinduced high spin states. The author believes that understanding of mysterious equilateral triangle consisting of thermal spin crossover on the first edge, photoinduced spin crossover on the second and structural diversity upon LS-HS transformation on the third edge can help approach the photoinduced spin transition under ambient conditions and so to their future technological applications. Keywords: finite-temperature behaviour; light-induced excited spin state trapping; LS-HS transformation; photoinduced spin transition; spin crossover