Irradiation with visible light converts Fe(II) polypyridines from their low-spin (singlet) to high-spin (quintet) state. This paper simulates the full singlet-triplet-quintet dynamics of the [Fe(terpy)₂]²⁺ complex to clarify the photodynamics. A branching mechanism is reported, involving two sequential processes: a dominant ³MLCT→³MC(³T₂g)→³MC(³T₁g)→⁵MC, and a minor ³MLCT→³MC(³T₂g)→⁵MC component. The quintet state is populated on the sub-picosecond timescale with non-exponential dynamics and coherent Fe-N breathing oscillations. Results agree with experimental data on Fe(II) polypyridines.

Tamás Rozgonyi, György Vankó, Mátyás Pápai