This presentation will focus on the excited state behavior of semiconductor nanocrystals as light absorbers that, coupled with redox catalysts, drive light-driven multi-electron transfer reactions. Reactions of interest include hydrogen generation, carbon dioxide reduction, nitrogen fixation, and water oxidation. We have demonstrated that nanocrystal excited state behavior, charge transfer dynamics, and surface chemistry play a governing role in the overall photochemistry of nanocrystal-catalyst complexes. This presentation will describe our most recent findings about how the reactions of interest can be driven and controlled through manipulation of nanocrystal excited state dynamics. In particular, the presentation will focus on: (i) measurement (by transient absorption spectroscopy), kinetic modeling, and control of electron transfer kinetics for injection of photoexcited electrons into redox enzymes; and (ii) elucidation of the motion of photoexcited holes on nanocrystal surfaces, using a combination of transient absorption measurements, modeling, and theory, and the implications of this motion on oxidation photochemistry.