1 E ff ect of Chiral Ligand Concentration and 2 Binding Mode on Chiroptical Activity of CdSe/ 3 CdS Quantum Dots

: Chiroptically active fl uorescent semiconductor nano-12 crystals, quantum dots (QDs), are of high interest, from a 13 theoretical and technological point of view, because they are 14 promising candidates for a range of potential applications. Optical 15 activity can be induced in QDs by capping them with chiral 16 molecules, resulting in circular dichroism (CD) signals in the range 17 of the QD ultraviolet − visible (UV-vis) absorption. However, the 18 e ff ects of the chiral ligand concentration and binding modes on the 19 chiroptical properties of QDs are still poorly understood. In the 20 present study, we report the strong in fl uence of the concentration of 21 a chiral amino acid (cysteine) on its binding modes upon the 22 surface of CdSe/CdS QDs, resulting in varying QD chiroptical 23 activity and corresponding CD signals. Importantly, we demon-24 strate that the increase of cysteine concentration is accompanied by 25 the growth of the QD CD intensity, reaching a certain critical point, after which it starts to decrease. The intensity of the 26 CD signal varies by almost an order of magnitude across this range. Nuclear magnetic resonance and Fourier transform 27 infrared data, supported by density functional theory calculations, reveal a change in the binding mode of cysteine 28 molecules from tridentate to bidentate when going from low to high concentrations, which results in a change in the CD 29 intensity. Hence, we conclude that the chiroptical properties of QDs are dependent on the concentration and binding 30 modes of the capping chiral ligands. These fi ndings are very important for understanding chiroptical phenomena at the 31 nanoscale and for the design of advanced optically active nanomaterials. 32