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., α-alkylation of aldehydes catalyzed by colloidal CsPbBr₃ nanocrystals (NCs). We find that both electrons and holes undergo ultrafast charge transfer (∼50 ps) from photoexcited perovskite NCs to reactant molecules. A charge separated state lives for more than 0.8 μs, enabling a radical mechanism to form the C–C bonds. We discuss the differences between the NCs photoredox catalysts and the molecular catalyst.