Chiral 3D CdSe Nanotetrapods

Three-dimensional (3D) nanomaterials have been intensively investigated because of their unique properties and wide range of potential applications; however, the ligand-induced chirality in 3D semiconductor nanocrystals has been scarcely studied. In this paper, we report the synthesis of hydrophobic 3D CdSe nanotetrapods (Tps) with a high degree of uniformity in their morphology by using the hot-injection method. The core and arms of Tps are distinct in their crystal structure, thus creating an intracrystal heterojunction. The size of Tps, primarily the length of four arms, is controlled by changing the amount of didecyldimethylammonium bromide and reaction time. Next, enantiopure cysteine ligands were introduced to replace the hydrophobic native stabilizers to prepare chiral l- and d-cysteine-capped CdSe Tps. Importantly, the circular dichroism (CD) line shapes of l/d-cysteine-capped CdSe Tps are assigned to the different excitonic transitions of the core and arms, respectively. In addition, the observed CD activities are found to be sensitive to the size of the CdSe Tps, where the anisotropic g factors have increased and reached the maximum value at a moderate aspect ratio (AR) and a further increase of the AR leads to a decrease of the g factor. Because of charge transfer between the core and arms, we propose a plausible mechanism potentially responsible for the induced CD line shapes in terms of the excitonic states of Tps with two different crystal structures. We believe that chiral 3D nanomaterials with anisotropic morphologies could offer new opportunities for relevant applications.