Quasi-reversible photoinduced displacement of aromatic ligands from semiconductor nanocrystals

Organic-inorganic nanohybrids using semiconductor nanocrystals (NCs) coordinated with aromatic organic molecules have been widely studied in the fields of optoelectronic materials, such as solar cells, photocatalysis, and photon upconversion. In these materials, coordination bonds of ligand molecules are usually assumed to be stable during optical processes. However, this assumption is not always valid. In this study, we demonstrate that the coordination bonds between ligand molecules and NCs by carboxyl groups are displaced quasi-reversibly by light irradiation using zinc sulfide (ZnS) NCs coordinated with perylenebisimide (PBI) as a model system. Ultrafast spectroscopy and density functional theory calculations show that the photoinduced ligand displacement is driven by ultrafast hole transfer from PBI to ZnS NCs, and that the dissociated radical anion of PBI survives over the second timescale. This study opens up a new avenue for advanced photofunctional materials utilizing colloidal NCs, such as photocatalysts that can expose their active facets of NCs on demand, and sub-micropatterning of photoconductive circuits on solid-state NC films.