(Invited) Ultrafast Spectroscopy Measurements of Lead-Halide Hybrid Semiconductor Nanocrystals for Photocatalysis

Abstract

We are exploring the use of metal-halide perovskite semiconductor nanocrystals (PNCs) as efficient photocatalysis. Heterogeneous photocatalysis are less common than homogeneous but can provide unique avenues for inducing novel chemical transformations and can also be utilized for energy transductions, i.e., the energy in the photons can be captured in chemical bonds. Additional, earth abundant nanocrystal based photocatalyst are highly sought after as they can potentially eliminate expensive noble metal catalyst. A detailed understand of the underlying reaction mechanism could provide guidance in designing new systems that can activate a larger class of small molecules. Here, we discuss transient absorption spectroscopy to study a model C-C bond formation reaction, i.e., alkylation of aldehydes catalyzed by colloidal CsPbBr3 NCs. We find that both electrons and holes undergo ultrafast charge transfer from photoexcited PNCs. After charge transfer the charge separated state lives ~ 1 ns enabling radical mechanism to form C-C bonds. I will also discuss the use of PNCs to host a transition metal Cu-site incorporated at the surface of the PNCs to induce a to induce a N-N heterocyclization reaction. The reaction starts from surface coordinated diamine substrates and requires to subsequent photo-oxidation events. We established a photocatalytic cycle where photo-excited holes are funneled to the coordinated substrates.