Fluorescence and Optical Activity of Chiral CdTe Quantum Dots in Their Interaction with Amino Acids

Guangmin Li, Xuening Fei, Hongfei Liu, Jing Gao, Jiayang Nie, Yuanbo Wang, Zhaodong Tian, Caicai He, Jiang Long Wang, Chao Ji, Dan Oron, Gaoling Yang

Research output: Contribution to journalArticle

Abstract

Ligand-induced chirality in semiconducting nanocrystals has been the subject of extensive study in the past few years and shows potential applications in optics and biology. Yet, the origin of the chiroptical effect in semiconductor nanoparticles is still not fully understood. Here, we examine the effect of the interaction with amino acids on both the fluorescence and the optical activity of chiral semiconductor quantum dots (QDs). A significant fluorescence enhancement is observed for l/d-Cys-CdTe QDs upon interaction with all the tested amino acids, indicating suppression of nonradiative pathways as well as the passivation of surface trap sites brought via the interaction of the amino group with the CdTe QDs' surface. Heterochiral amino acids are shown to weaken the circular dichroism (CD) signal, which may be attributed to a different binding configuration of cysteine molecules on the QDs' surface. Furthermore, a red shift of both CD and fluorescence signals in l/d-Cys-CdTe QDs is only observed upon adding cysteine, while other tested amino acids do not exhibit such an effect. We speculate that the thiol group induces orbital hybridization of the highest occupied molecular orbital (HOMOs) of cysteine and the valence band of CdTe QDs, leading to the decrease of the energy band gap and a concomitant red shift of CD and fluorescence spectra. This is further verified by density functional theory calculations. Both the experimental and theoretical findings indicate that the addition of ligands that do not "directly" interact with the valence band (VB) of the QD (noncysteine moieties) changes the QD photophysical properties, as it probably modifies the way cysteine is bound to the surface. Hence, we conclude that it is not only the chemistry of the amino acid ligand that affects both CD and PL but also the exact geometry of binding that modifies these properties. Understanding the relationship between the QD's surface and chiral amino acid thus provides an additional perspective on the fundamental origin of induced chiroptical effects in semiconductor nanoparticles, potentially enabling us to optimize the design of chiral semiconductor QDs for chiroptic applications.

Original languageEnglish
Pages (from-to)4196-4205
Number of pages10
JournalACS nano
Volume14
Issue number4
DOIs
Publication statusPublished - Apr 28 2020

Keywords

  • chiral
  • circular dichroism
  • fluorescence
  • orbital hybridization
  • quantum dots
  • thiol group

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

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  • Cite this

    Li, G., Fei, X., Liu, H., Gao, J., Nie, J., Wang, Y., Tian, Z., He, C., Wang, J. L., Ji, C., Oron, D., & Yang, G. (2020). Fluorescence and Optical Activity of Chiral CdTe Quantum Dots in Their Interaction with Amino Acids. ACS nano, 14(4), 4196-4205. https://doi.org/10.1021/acsnano.9b09101