Significance Far-red photosystem II (FR-PSII) contains a small number of FR-chlorophylls (- f or - d ) with the rest (∼85%) being chlorophyll- a molecules. Here ultrafast studies on FR-PSII support a model in which the primary electron donor is a FR-chlorophyll (P ₇₂₀ , likely in the Chl _D1 position), while the second electron donor is chlorophyll- a at the P _D1 position, forming P _D1 ^+• . Excitation energy transfer from chlorophyll- a to the FR-chlorophylls is ultrafast. The excited state of FR-chlorophyll remains highly localized, i.e., P ₇₂₀ * does not share the excitation with the chlorophyll- a pigments. This is markedly different from both the conventional, chlorophyll- a PSII, and the chlorophyll- d PSII of Acaryochloris marina . The entropic and site-energy differences result in efficient but apparently slower stabilization of the charge-separated state.