Controlled nanocrystallization of gold nanoclusters within surfactant envelopes: enhancing aggregation-induced emission in solution

• Published in: Chemical Science Vol. 15; no. 3; pp. 11775 - 11782
• Main Authors: Saito, Yuki, Suda, Ayano, Sakai, Maki, Nakajima, Shogo, Shichibu, Yukatsu, Kanai, Hayato, Ishida, Yasuhiro, Konishi, Katsuaki
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry (RSC) 31.07.2024; Royal Society of Chemistry; The Royal Society of Chemistry
• Subjects: Agglomeration; Aqueous solutions; Chemical synthesis; Chemistry; Crystal growth; Crystallization; Emission; Envelopes; Gold; Nanoclusters; Nanocrystals; Nanomaterials; Phosphines; Photoluminescence; Robust control; Shell stability; Sodium dodecyl sulfate; Surfactants
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d4sc02834a

The nanocrystallization of functional molecules has been a subject of recent interest in the current development of nanotechnology. Herein, we report the unprecedented synthesis of single nanocrystals of a molecular gold nanocluster in a homogeneous solution by using surfactant-based nano-envelopes. The co-assembling of a Au 8 nanocluster carrying lipophilic phosphine ligands with sodium dodecyl sulfate (SDS) in an aqueous solution results in the formation of sphere-shaped amorphous nano-aggregates coated with the surfactant. Upon sonication, the spherical amorphous aggregates are smoothly shape-shifted into discrete rhombic nanocrystals, which can be tracked by TEM and solution XRD. The transformation into single nanocrystals occurs exclusively without further growth or agglomeration, implying that the crystal growth is restricted within the surfactant nano-envelopes. The robust but flexible nature of the wrapped surfactant is likely responsible for the controlled crystallization. We also demonstrate that the amorphous-to-nanocrystalline transition in solution remarkably enhances the photoluminescence emission from the nanocluster, providing a clear example of crystallization-induced emission enhancement. Notably, the obtained nanocrystals showed high stability in solution and retained their shape, size, and PL intensity even after several months, owing to the densely packed surfactant shell. The present surfactant-directed nanocrystallization method may be applicable to other molecular species to contribute to the development of nanocluster science as well as the designed synthesis of nanomaterials. Sphere-shaped amorphous aggregates of Au 8 clusters entrapped within SDS nanoenvelopes are transformed into rhombic single nanocrystals upon simple sonication in solution, where the aggregation-induced emission (AIE) from Au 8 is notably enhanced.