The critical role played by the catalytic moiety in the early-time photodynamics of hydrogen generating bimetallic photocatalysts

The effect of the catalytic moiety on the early-time photodynamics of Ru/M (M=Pt or Pd) bimetallic photocatalysts is studied by ultrafast transient absorption spectroscopy. In comparison to the Ru/Pd photocatalyst described earlier, the Ru/Pt analogue shows complex excited-state dynamics with three distinct kinetic components ranging from sub-ps to 102 ps, requiring a more sophisticated photophysical model than that developed earlier for the Ru/Pd complex. In the Pu/Pt photocatalyst, an additional lower-lying excited state is proposed to quench the hot higher-lying triplet metal-to-ligand chargetransfer states. Furthermore, a strong excitation wavelength dependence on the population of excited states is observed for both the Ru/Pt and Ru/Pd complexes, indicating a nonequilibrated distribution even on the 102 ps timescale. These insights shed light on the significant impact of the catalytic moiety on the fundamental early-time photophysics of Rubased photocatalysts.