School of Chemistry, CRANN and AMBER Research Centres , Trinity College Dublin , College Green, Dublin 2 , Ireland.
ITMO University , St. Petersburg 197101 , Russia.
ACS Nano. 2019 Nov 26;13(11):13560-13572. doi: 10.1021/acsnano.9b07513. Epub 2019 Nov 13.
Chiroptically active fluorescent semiconductor nanocrystals, quantum dots (QDs), are of high interest from a theoretical and technological point of view, because they are promising candidates for a range of potential applications. Optical activity can be induced in QDs by capping them with chiral molecules, resulting in circular dichroism (CD) signals in the range of the QD ultraviolet-visible (UV-vis) absorption. However, the effects of the chiral ligand concentration and binding modes on the chiroptical properties of QDs are still poorly understood. In the present study, we report the strong influence of the concentration of a chiral amino acid (cysteine) on its binding modes upon the surface of CdSe/CdS QDs, resulting in varying QD chiroptical activity and corresponding CD signals. Importantly, we demonstrate that the increase of cysteine concentration is accompanied by the growth of the QD CD intensity, reaching a certain critical point, after which it starts to decrease. The intensity of the CD signal varies by almost an order of magnitude across this range. Nuclear magnetic resonance and Fourier transform infrared data, supported by density functional theory calculations, reveal a change in the binding mode of cysteine molecules from tridentate to bidentate when going from low to high concentrations, which results in a change in the CD intensity. Hence, we conclude that the chiroptical properties of QDs are dependent on the concentration and binding modes of the capping chiral ligands. These findings are very important for understanding chiroptical phenomena at the nanoscale and for the design of advanced optically active nanomaterials.
手性荧光半导体纳米晶，即量子点（QDs），从理论和技术角度来看都非常有趣，因为它们是一系列潜在应用的有前途的候选材料。通过用手性分子对 QD 进行封端，可以在手性荧光半导体纳米晶中诱导出光学活性，从而在 QD 的紫外-可见（UV-vis）吸收范围内产生圆二色性（CD）信号。然而，手性配体浓度和结合模式对 QD 手征光学性质的影响仍未得到很好的理解。在本研究中，我们报告了手性氨基酸（半胱氨酸）浓度对手性氨基酸在 CdSe/CdS QD 表面的结合模式的强烈影响，导致 QD 手征光学活性和相应的 CD 信号发生变化。重要的是，我们证明了半胱氨酸浓度的增加伴随着 QD CD 强度的增加，达到一定的临界点后，它开始下降。在这个范围内，CD 信号的强度变化了近一个数量级。核磁共振和傅里叶变换红外数据，以及密度泛函理论计算的支持，揭示了当半胱氨酸分子从低浓度到高浓度时，其结合模式从三配位变为二配位，从而导致 CD 强度发生变化。因此，我们得出结论，QD 的手征光学性质取决于封端手性配体的浓度和结合模式。这些发现对于理解纳米尺度的手征光学现象以及设计先进的手征光学纳米材料非常重要。
