Semiconductor nanocrystals – which can behave electronically as quantum dots – are a versatile way to turn incident light into fluorescence, electricity, and storable fuels because of their size-tunable properties. Appropriate surface termination and linking chemistry can be used to control the flow of energy and charge within and among nanocrystals and molecules, as has been demonstrated in the case of ratiometric chemical sensors and optoelectronic devices formed of colloidal quantum dots. Despite this promise, the nanocrystal surface is complex and dynamic, subject to ligand exchange with surrounding medium. Purification methods and characterization techniques that permit assemblies of increasing complexity to be formed in a highly repeatable and verifiable fashion are key to revealing the full potential of colloidal nanocrystals in these and other areas.
The Greytak group has used gel permeation chromatography (GPC) as a means to separate nanocrystals from small molecules. We have shown that GPC is an effective way to isolate nanocrystals with low and consistent ligand populations without requiring a change in solvent, and to drive nanocrystal ligand exchange reactions in situ through continuous separation of soluble products. Our lab has demonstrated these concepts using cadmium selenide-based nanocrystals. A current challenge is to translate the progress that has been made in CdSe and other II-VI nanocrystal surface chemistry and photophysics to inorganic semiconductors that can meet 21st century challenges. This includes materials that can be sustainably scaled for efficient solar energy conversion, and materials with diminished use of toxic elements. In this talk I will describe ongoing work, enabled by GPC, to expand the material scope for detailed understanding of nanocrystal surface chemistry.