Department of Molecular, Cellular, and Biomedical Sciences, University of New Hampshire , 46 College Road, Durham, New Hampshire 03824, United States.
Department of Chemistry, University of Wyoming , 1000 East University Avenue, Laramie, Wyoming 82071, United States.
ACS Nano. 2017 Oct 24;11(10):9846-9853. doi: 10.1021/acsnano.7b03555. Epub 2017 Oct 2.
Functionalization of colloidal quantum dots (QDs) with chiral cysteine derivatives by phase-transfer ligand exchange proved to be a simple yet powerful method for the synthesis of chiral, optically active QDs regardless of their size and chemical composition. Here, we present induction of chirality in CdSe by thiol-free chiral carboxylic acid capping ligands (l- and d-malic and tartaric acids). Our circular dichroism (CD) and infrared experimental data showed how the presence of a chiral carboxylic acid capping ligand on the surface of CdSe QDs was necessary but not sufficient for the induction of optical activity in QDs. A chiral bis-carboxylic acid capping ligand needed to have three oxygen-donor groups during the phase-transfer ligand exchange to successfully induce chirality in CdSe. Intrinsic chirality of CdSe nanocrystals was not observed as evidenced by transmission electron microscopy and reverse phase-transfer ligand exchange with achiral 1-dodecanethiol. Density functional theory geometry optimizations and CD spectra simulations suggest an explanation for these observations. The tridentate binding via three oxygen-donor groups had an energetic preference for one of the two possible binding orientations on the QD (111) surface, leading to the CD signal. By contrast, bidentate binding was nearly equienergetic, leading to cancellation of approximately oppositely signed corresponding CD signals. The resulting induced CD of CdSe functionalized with chiral carboxylic acid capping ligands was the result of hybridization of the (achiral) QD and (chiral) ligand electronic states controlled by the ligand's absolute configuration and the ligand's geometrical arrangement on the QD surface.
通过相转移配体交换，将胶体量子点（QD）与手性半胱氨酸衍生物功能化，被证明是一种简单而强大的方法，可以合成手性、光学活性的 QD，而与 QD 的大小和化学成分无关。在这里，我们提出了通过硫醇免费手性羧酸封端配体（l-和 d-苹果酸和酒石酸）诱导 CdSe 的手性。我们的圆二色性（CD）和红外实验数据表明，手性羧酸封端配体在 CdSe QD 表面的存在是诱导 QD 光学活性的必要条件，但不是充分条件。手性双羧酸封端配体在手性羧酸封端配体在相转移配体交换中需要具有三个供氧基团，才能成功地诱导 CdSe 的手性。正如透射电子显微镜和与非手性 1-十二硫醇的反向相转移配体交换所证明的那样，CdSe 纳米晶体没有观察到固有手性。密度泛函理论几何优化和 CD 光谱模拟为这些观察结果提供了一个解释。通过三个供氧基团的三齿结合在手性羧酸封端配体与 CdSe 之间具有能量偏好，从而导致 CD 信号。相比之下，二齿结合几乎是等能量的，导致大致相反符号的相应 CD 信号相互抵消。用手性羧酸封端配体制备的 CdSe 的诱导 CD 是由配体的绝对构型和配体在 QD 表面上的几何排列控制的（非手性）QD 和（手性）配体电子态的杂化产生的。
