Abstract
We explain theoreticallythe peculiarities of photoinduced low-spin (LS)→high-spin (HS) transitions in spin-crossover complexes, such as the threshold behavior in the excitation light intensity for phase conversionand the existence of the incubation period.Our investigation is based on a modelwhere a single complex is described by the two electronic states and the breathing oscillation mode with the long-range interaction among the complexes.As the spin transition processes, we take into accountthe LS→HS photoexcitation processand the HS→LS nonradiative decay process.The rate for the latter process is sensitive to the LS fraction in the crystalbecause the potential barrier for the HS→LS decayis dependent on the LS fraction through the long-range interaction amongthe complexes;the lifetime of the metastable HS state becomes longeras the LS fraction decreases.Such sensitivity leads to the nonlinear temporal evolution for the LSfraction, which coincides with the experimental results.
