Fluorescence and Optical Activity of Chiral CdTe Quantum Dots in Their Interaction with Amino Acids
Open Access
- 28 April 2020
- journal article
- research article
- Published by American Chemical Society (ACS) in ACS Nano
- Vol. 14 (4), 4196-4205
- https://doi.org/10.1021/acsnano.9b09101
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.Keywords
Funding Information
- Tianjin Science and Technology Committee (15ZCZDSF00150)
- National Natural Science Foundation of China (51578360, 51778398)
- Tianjin High School Science and Technology Fund Planning Project (170401017)
This publication has 50 references indexed in Scilit:
- Effect of Chiral Ligand Concentration and Binding Mode on Chiroptical Activity of CdSe/CdS Quantum DotsACS Nano, 2019
- CdSe Quantum Dots Functionalized with Chiral, Thiol-Free Carboxylic Acids: Unraveling Structural Requirements for Ligand-Induced ChiralityACS Nano, 2017
- Impact of Shell Thickness on Photoluminescence and Optical Activity in Chiral CdSe/CdS Core/Shell Quantum DotsACS Nano, 2017
- Cooperative expression of atomic chirality in inorganic nanostructuresNature Communications, 2017
- Spin Selective Charge Transport through Cysteine Capped CdSe Quantum DotsNano Letters, 2016
- Chirality Inversion of CdSe and CdS Quantum Dots without Changing the Stereochemistry of the Capping LigandACS Nano, 2016
- Ligand Induced Circular Dichroism and Circularly Polarized Luminescence in CdSe Quantum DotsACS Nano, 2013
- Achiral CdSe quantum dots exhibit optical activity in the visible region upon post-synthetic ligand exchange with d- or l-cysteineChemical Communications, 2013
- Chiral recognition in dimerization of adsorbed cysteine observed by scanning tunnelling microscopyNature, 2002
- Chiral discrimination by chemical force microscopyNature, 1998