Trap states induced by chalcogenide vacancies in defective transition metal dichalcogenide (TMDs) monolayers are detrimental to both the charge carrier lifetime and device efficiency. To address this, chemically functionalizing the surface of defective TMD monolayers is crucial. Experimental methods such as thiol grafting on chalcogenide vacancies, oxygen passivation, and the physisorption of electroactive molecules have been explored for defect healing. Our study, using ab initio time-domain density functional theory and nonadiabatic molecular dynamics, shows that C