Tailoring the Fluorescent and Electronic Properties of 2H-MoS₂ by Step-by-Step Functionalization

Two-dimensional layered MoS₂ has attracted tremendous attention because of its unique physical and chemical properties and promising application prospects. To further expand its applications to areas such as gas sensing, biosensing, drug delivery, and photothermal therapy, surface functionalization has been employed to engineer its properties according to multiple perspectives. Herein, we demonstrate a scalable surface modification method to generate functionalized MoS₂ flakes by the step-by-step covalent assembly of lipoic acid (LA) and fluorescein isothiocyanate (FITC) molecules. In our approach, reactive disulfide-containing LA molecules were first chemically bonded to the sulfur vacancies (SVs) of MoS₂ surfaces. FITC was then linked to MoS₂ through LA by a condensation reaction between the amino group of FITC and the carboxyl group of LA. It was demonstrated that the initial LA functionalization enhanced the electronic mobility via the filling of SVs, and the second-step functionalization with FITC induced electron doping of MoS₂. Moreover, the covalent attachment of FITC decorated the PL spectrum of MoS₂ with an additional green fluorescence at ∼530 nm. This strategy is a universal route to construct a versatile platform for chemical modification of functional groups and provides new opportunities of controlling the electronic and optical properties of transition-metal dichalcogenides.