Circular Dichroism of CdSe Nanocrystals Bound by Chiral Carboxylic Acids

Abstract

Chiral semiconductor nanocrystals, or quantum dots (QDs), are promising materials for applications in biological sensing, photonics, and spin-polarized devices. Many of these applications rely on large dissymmetry, or g-factors, the difference in absorbance between left- and right-handed circularly polarized light compared to the unpolarized absorbance. The majority of chiral QDs, specifically CdSe, reported to date have used thiolated amino acid ligands to introduce chirality onto the nanoparticles, but these systems have ultimately reported small g-factors of ∼2 × 10. In an effort to realize chiral CdSe QDs with higher g-factors and to expand the set of designer chiral semiconductor nanocrystals, we have employed chiral carboxylic acids as a distinct class of ligands for chiral CdSe nanoparticles. Through this family of chiral carboxylic acid ligands, we performed a direct comparison between carboxylate-bound and thiolate-bound chiral CdSe QDs. Spectral analysis revealed that the resulting circular dichroism shifts originate from the splitting of the exciton by the ligand-nanocrystal interaction. Subsequent examination of a series of chiral carboxylic acid ligands revealed a 30-fold range in g-factor through relatively small changes in the structure of the ligand. Finally, we showed that increasing the number of stereocenters on the ligand can further enhance the dissymmetry factors. This versatile and tunable combination of nanocrystals and ligands will inform future designs of chiral nanomaterials and their applications.

Chiral 2D Colloidal Semiconductor Quantum Wells

“…The more recently developed method for fabrication of chiral QDs through postsynthesis ligand exchange, dramatically increased the ability to study induced chirality in shaped QDs and heterostructured QDs and extend the range of chiral ligands used in the process . These recent studies shed more light on the mechanisms underlying the induction of chirality …”

“…By surveying the magnitude of induced chirality for a family of designed chiral carboxylic acids, it was shown that the nature of the binding site and the ensuing chiral distortion of the nanoparticle are of importance . Studies of induced chirality on CdSe/CdS heterostructure core/shell QDs with increasing shell thickness showed a decrease in the induced chirality as the shell thickness was increased .…”

Chirality‐Based Biosensors

“…The fabrication of optically active NPs has attracted significant attention over the past decade. Optically active QDs, semiconductor nanorods (SNRs), chiromagnetic NPs, optically active metal NPs, and chiral Ag nanowires, as well as other optically active nanostructures (e.g., twisted α‐HgS and MoS 2 , graphene) . have been created by synthetic technology.…”

Spectroscopy for model heterogeneous asymmetric catalysis

“…Different aspects of this phenomenon have been elucidated frequently in multiple excellent contributions for metallic [84][85][86][87][88][89][90][91][92][93][94][95][96][97][98] and semiconducting nanoparticles. [99][100][101][102][103][104][105][106][107][108][109] Ma and coworkers summarized most of the works related to chirality transfer in 2017 where they considered four types of chirality in nanoparticles and gave examples of each. 110 The four types are the following: (1) geometrical chirality of the inorganic core, (2) geometrical chirality of the inorganic surface (also called chiral footprint), (3) geometrical chirality of the protecting shell, and (4) chiral field effect.…”