Electron Transfer into Electron-Accumulated Nanocrystals: Mimicking Intermediate Events in Multielectron Photocatalysis II

The overall efficiency of multielectron photocatalytic reactions is often much lower than the charge-separation yield reported for the first charge-transfer (CT) event. Our recent study has partially linked this gap to CT from charge-accumulated light harvesters. Another possible intermediate event lowering the efficiency is CT into charge-accumulated nanocatalysts. To study this event, we built a "toy" system using nanocrystal quantum dots (QDs) doped with extra electrons to mimick charge-accumulated nanocatalysts. We measured electron transfer (ET) from photoexcited molecular light harvesters into doped QDs using transient absorption spectroscopy. The measurements reveal that the pre-existing electron slows down ET from 37.8 ± 2.2 ps in the neutral sample to 93.4 ± 8.6 ps in the singly doped sample, accelerates charge recombination (CR) from 7.02 ± 0.84 to 3.69 ± 0.25 ns, and lowers the electron-injection yield by ∼14%. This study uncovers yet another possible intermediate event lowering the efficiency of multielectron photocatalysis.