Theory of the photoinduced spin-state transitions in spin-crossover complexes

Nonlinear properties observed during the photoinjection of high-spin (HS) domains into a low-spin (LS) phase in spin-crossover complexes are explained theoretically. As the spin-transition processes, we take into account the LS --> NS photoexcitation process and the WS --> LS nonradiative decay process. The latter one is sensitive to the LS fraction in the crystal; the lifetime of the metastable HS state becomes longer as the LS fraction decreases. Such sensitivity results in the nonlinear temporal evolution for the LS fraction, which qualitatively explains experimental results. (C) 2000 Elsevier Science B.V. All rights reserved.