Ultrafast Reaction Mechanisms in Perovskite Based Photocatalytic C-C Coupling

Solar driven carbon-carbon (C-C) bond formation is a new direction in solar energy utilization. Earth abundant nanocrystal based photocatalysts are highly sought after as they can potentially eliminate expensive noble metal catalysts. A detailed understanding of the underlying reaction mechanisms could provide guidance in designing new systems that can activate a larger class of small molecules. Here, we employ transient absorption spectroscopy to study a model C-C bond formation reaction, i.e., alpha-alkylation of aldehydes catalyzed by colloidal CsPbBr3 nanocrystals (NCs). We find that both electrons and holes undergo ultrafast charge transfer (similar to 50 ps) from photoexcited perovskite NCs to reactant molecules. A charge separated state lives for more than 0.8 mu s, enabling a radical mechanism to form the C-C bonds. We discuss the differences between the NCs photoredox catalysts and the molecular catalyst.