Publication date: 15th May 2025
Charge transfer from semiconductor nanocrystals (NCs) is the requisite first step in NC-driven photocatalysis. Subsequent charge recombination limits the accumulation of charges needed to drive catalysis. Here, we demonstrate the substantial impact of covalent binding of a hole acceptor to the NC surface on the charge recombination lifetime within the NC. NMR spectroscopy reveals that, unlike underivatized phenothiazine, the addition of a short carboxylate binding group to phenothiazine enables the molecule to bind strongly to the CdS NC surface. Transient absorption spectroscopy of these functionalized CdS NCs reveals unity efficiency of hole transfer to the derivatized phenothiazine and the longest charge separation lifetimes reported for Cd-chalcogenide NCs, 1.7 ms charge-separation lifetime in CdS quantum dots and 24.3 ms in CdS nanorods. We calculate that such long charge-separation lifetimes could enhance the quantum efficiencies of subsequent electron transfer up to 43-fold. Unfunctionalized phenothiazine has a significantly smaller impact on the charge dynamics, with only 13% hole-transfer efficiency and a 52 ns charge-separation lifetime. We attribute the increase in hole transfer efficiency and charge separation lifetime to the strong covalent binding of the carboxylated phenothiazine. This surface functionalization provides a highly generalizable approach to improving NC photocatalysis that could be implemented in tandem with electron-acceptors, more complex nanocrystal heterostructures, and catalysts.
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