Excited States Electronic Coupling, and Charge Transfer Properties of Chalcogenide-Capped Semiconductor Nanocrystals
Abstract
The objective of this project was to investigate the excited-state and charge transfer properties of semiconductor nanocrystals functionalized with ultrashort chalcogenide surface-capping ligands (S2, Se2, and Te2). Colloidal nanocrystals are typically synthesized with long-chain aliphatic molecules, which bind relatively strongly to the nanocrystal surface, thereby passivating and solubilizing the nanocrystal. However, these long, aliphatic surface ligands also weaken the electronic coupling between the nanocrystal and its environment. This is undesirable for applications involving charge transfer. Ultrashort ligands are therefore of great interest, as they allow strong electronic coupling while maintaining the nanocrystal's stability and solubility. However, the effect of ultrashort ligands on the excited states and particularly on charge transfer in nanocrystal systems had not been explored. In this project, we combined theory with experimental work employing steady state and ultrafast optical spectroscopy to examine how these ligands affect the excited states, electronic coupling, and charge transfer in nanocrystals. We found that binding and unbinding of ultrashort ligands on the nanocrystal surface can introduce electron traps and that these electron traps can enable co-catalyst-free photochemistry by the nanocrystal. We developed a simple analysis to extract the biexciton spectra and lifetime from transient absorption (TA) dynamics and demonstrated that decreased electron-hole wavefunction overlap in S2 capped CdSe quantum dots (QDs) slows down Auger recombination. Using S2 capped CdS nanorods (NRs), we demonstrated enhanced electron transfer to hydrogenase enzyme by three orders of magnitude over MPA capped NRs, which we attribute to stronger electronic coupling enabled by the shorter S2 ligand.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 27, 2019
- Accession Number
- AD1086090
Entities
People
- Gordana Dukovic
Organizations
- Regents of the University of Colorado