Ultrafast intersystem crossings in Fe-Co Prussian blue analogues

Abstract 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 $$S{\boldsymbol{=}}\frac{{\bf{3}}}{{\bf{2}}}$$ S = 3 2 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.