Robust Basal-Plane Functionalization with Masked <i>N</i> -Heterocyclic Carbenes Gives Semiconducting MoS ₂ and WS ₂ Nanoflakes

Tailoring the surface characteristics of layered transition metal dichalcogenides (LTMDs) is critical for optimizing performance for integration into advanced technological devices. Group VI LTMDs offer exceptional potential in fields such as optoelectronics, energy storage, and sensing. However, their fully occupied valence band poses challenges in establishing strong interfacial interactions and facilitating composite formation. Herein, we report a strategy for basal-plane functionalization of Group VI LTMDs using masked N-heterocyclic carbenes (NHCs). As mild nucleophiles, NHCs facilitate electron transfer into the unoccupied conduction band while preserving structural integrity and the semiconducting properties of the LTMDs such as MoS2 and WS2. The elevated electron density enables the functionalization and the formation of a bilayer self-assembled monolayers of NHC precursors on the surface of the few-to-monolayer LTMDs through ionic interactions, leading to restacked superlattice structures. Notably, the masked NHC layers effectively suppress interlayer coupling, thereby maintaining the monolayer-like semiconducting behavior in the restacked materials. The robust interactions between masked NHCs and LTMDs, along with retention of semiconducting properties, is demonstrated in detail. These findings introduce a versatile method for surface modifications of LTMDs and establish a synthetic pathway to an emerging class of materials. This approach expands the functional applicability of LTMDs across diverse technological platforms.