Surface Doping Quantum Dots with Chemically Active Native Ligands: Controlling Valence without Ligand Exchange

Thumbnail Image
Supplemental Files
Tavasoli, Elham
Guo, Yijun
Kunal, Pranaw
Grajeda, Javier
Gerber, Allison
Major Professor
Committee Member
Journal Title
Journal ISSN
Volume Title
Vela, Javier
University Professor
Research Projects
Organizational Units
Organizational Unit
Ames National Laboratory

Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.

For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.

Organizational Unit

The Department of Chemistry seeks to provide students with a foundation in the fundamentals and application of chemical theories and processes of the lab. Thus prepared they me pursue careers as teachers, industry supervisors, or research chemists in a variety of domains (governmental, academic, etc).

The Department of Chemistry was founded in 1880.

Dates of Existence

Related Units

Journal Issue
Is Version Of

One remaining challenge in the field of colloidal semiconductor nanocrystal quantum dots is learning to control the degree of functionalization or "valence" per nanocrystal. Current quantum dot surface modification strategies rely heavily on ligand exchange, which consists of replacing the nanocrystal's native ligands with carboxylate- or amine-terminated thiols, usually added in excess. Removing the nanocrystal's native ligands can cause etching and introduce surface defects, thus affecting the nanocrystal's optical properties. More importantly, ligand exchange methods fail to control the extent of surface modification or number of functional groups introduced per nanocrystal. Here, we report a fundamentally new surface ligand modification or "doping" approach aimed at controlling the degree of functionalization or valence per nanocrystal while retaining the nanocrystal's original colloidal and photostability. We show that surface-doped quantum dots capped with chemically active native ligands can be prepared directly from a mixture of ligands with similar chain lengths. Specifically, vinyl and azide-terminated carboxylic acid ligands survive the high temperatures needed for nanocrystal synthesis. The ratio between chemically active and inactive-terminated ligands is maintained on the nanocrystal surface, allowing to control the extent of surface modification by straightforward organic reactions. Using a combination of optical and structural characterization tools, including IR and 2D NMR, we show that carboxylates bind in a bidentate chelate fashion, forming a single monolayer of ligands that are perpendicular to the nanocrystal surface. Moreover, we show that mixtures of ligands with similar chain lengths homogeneously distribute themselves on the nanocrystal surface. We expect this new surface doping approach will be widely applicable to other nanocrystal compositions and morphologies, as well as to many specific applications in biology and materials science.


Reprinted (adapted) with permission from Chemistry of Materials 24 (2012): 4231, doi: 10.1021/cm3026957. Copyright 2012 American Chemical Society.

Subject Categories
Sun Jan 01 00:00:00 UTC 2012