Post-synthetic ligand exchange with CdSe quantum dots (QDs) enables tuning of the optical band gap of the QDs by modulating interfacial interactions at the QD surface. We discuss two mechanisms by which post-synthetic ligand exchange affects the absorbance and emission energies of QDs, surface charge density in water and exciton delocalization in nonpolar organic solvents. Post-synthetic optical bandgap modification is advantageous for both photocatalytic and sensing applications with QDs, and we focus here on the potential for dynamic sensing in solution. Colorimetric mechanisms for sensing are desirable relative to mechanisms that rely upon photoluminescence intensity due to the non-specific nature of quenching or emission enhancement in QDs. Additionally, provided that the colorimetric sensing mechanism relies on the QD exciton confinement, the rate of dynamic sensing should be effectively instantaneous. We describe the use of N-heterocylic carbene-based ligands in toluene, which delocalize the QD exciton while maintaining the QD photoluminescence. This mechanism is ideal for dynamic colorimetric sensing. We compare this exciton delocalizing mechanism in toluene with a charge density-based mechanism for expanding the excitonic wavefunction in water. We use a combination of ground state optical spectroscopies and nuclear magnetic resonance spectroscopy to characterize the interfacial interactions in both toluene and water. We find that the mechanism by which exciton delocalization occurs affects the usefulness of the QD-ligand systems for either photocatalytic or sensing applications.

Post-synthetic ligand exchange modulates the absorbance and emission energies of colloidal CdSe quantum dots

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.