Ultrafast intersystem crossings in Fe-Co Prussian blue analogues

Ultrafast spincrossover is studied in Fe-Co Prussian blue analogues using a dissipative quantum-mechanical model of a cobalt ion coupled to a breathing mode. All electronic interactions are treated on an equal footing. It is theoretically demonstrated that the divalent cobalt ion reaches 90% of the [Formula: see text] value within 20 fs after photoexciting a low-spin Co(3+) ion by an iron-to-cobalt charge transfer. The doublet-to-quartet spin crossover is significantly faster than the oscillation period of the breathing mode. The system relaxes to the lowest manifold of divalent cobalt ((4) T (1)) in 150–200 fs. Strong oscillations in spin-orbit coupling and the involvement of higher-lying quartets are found.