Covalent Chemistry on a Van Der Waals Heterostructure

The building of van der Waals heterostructures and the decoration of 2D materials with organic molecules share a common goal: to obtain ultrathin materials with tailored properties. Performing controlled chemistry on van der Waals heterostructures would add an extra level of complexity, providing a pathway towards 2D-2D-0D mixed-dimensional heterostructures. Here we show that thiol-ene-like “click” chemistry can be used to decorate franckeite, a naturally occurring van der Waals heterostructure, with maleimide reagents. ATR-IR and NMR analyses corroborate the Michael addition mechanism via the formation of a S-C covalent bond, while Raman and HR-TEM show that the SnS₂-PbS alternating structure of franckeite is preserved, and suggest that SnS₂reacts preferentially, which is confirmed through XPS. We illustrate how this methodology can be used to add functional molecular moieties by decorating franckeite with porphyrins. UV-vis-NIR spectroscopy confirms that the chromophore remains operative and shows negligible electronic interactions with franckeite in the ground state, while its fluorescence is strongly quenched upon photoexcitation.