Covalent modification of franckeite with maleimides: connecting molecules and van der Waals heterostructures

Abstract

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 SnS₂ reacts 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 ground state remains operative, showing negligible ground-state interactions with the franckeite. Excited-state interactions across the hybrid interface are revealed. Time-resolved photoluminescence confirms the presence of excited-state deactivation in the linked porphyrin ascribed to energy transfer to the franckeite.