Post-synthetic phase transfer ligand exchange has been established as a simple, reliable, and versatile method for the synthesis of chiral, optically active colloidal nanocrystals displaying circular dichroism (CD) and circularly polarized luminescence (CPL). Herein we present a water-free and purification-free cyclohexane → methanol ligand exchange system that led to the synthesis of stable, non-aggregating chiral and fluorescent cadmium sulfide quantum dots (CdS QDs). Absorption and emission studies revealed that the carboxylate capping ligands can tune the band gap by up to 65 meV as well as control the band gap and deep trap emission pathways. The CD data revealed that the addition of a 2nd stereogenic center did not automatically lead to an increase of the CD anisotropy of QDs, but rather match/mismatch cooperativity effects must be considered in the transfer of the chirality from the capping ligands to the achiral nanocrystals. Variation in position of the functional groups as well as the chemical identity of the functional groups impacted both the shape and anisotropy of the induced CD spectra and revealed the importance of the functional groups’ coordination and polarity on the binding geometry and induced chiroptical properties. Finally, we describe the first example where CD spectra of QDs capped with the same ligand and dissolved in the same solvent displayed very different spectral profiles. This work provides deeper insight into induced CD of QDs and paves the path to rational design of chiral nanomaterials.
Bibliographical noteFunding Information:
This work was supported in part by the National Science Foundation (award CBET 1403947; KV), Yonsei University (MB) and the University of New Hampshire (KV, YHK, YAJ). The 700 MHz NMR was purchased by NSF MRI funds (award DBI 1828319; KV) with additional support from the UNH Center for Integrated Biomedical and Bioengineering Research (CIBBR), established through a grant from the National Institute of General Medical Sciences (NIGMS) of the National Institutes of Health (award P20GM113131). We thank Dr C. A. Caputo and C. Wilson (UNH) for their assistance with time resolved fluorescence. YHK thanks the Summer Teaching Assistant Fellowship from the University of New Hampshire.
© The Royal Society of Chemistry 2021.
All Science Journal Classification (ASJC) codes
- Materials Chemistry