N-Heterocyclic Carbenes as Reversible Exciton-Delocalizing Ligands for Photoluminescent Quantum Dots

Delocalization of excitons within semiconductor quantum dots (QDs) into states at the interface of the inorganic core and organic ligand shell by so-called “exciton-delocalizing ligands (EDLs)” is a promising strategy to enhance coupling of QD excitons with proximate molecules, ions or other QDs. EDLs thereby enable enhanced rates of charge carrier extraction from, and transport among, QDs and dynamic colorimetric sensing. The application of reported EDLs – which bind to the QD through thiolates or dithiocarbamates – is however limited by the irreversibility of their binding and their low oxidation potentials, which lead to a high yield of photoluminescence-quenching hole trapping on the EDL. This article describes a new class of EDLs for QDs, 1,3-dimethyl-4,5-disubstituted imidazolylidene N-heterocyclic carbenes (NHCs), where the 4,5 substituents are either Me, H, or Cl. Post-synthetic ligand exchange of native oleate capping ligands for NHCs results in a bathochromic shift of the optical band gap of CdS...