Evolution of Photoluminescent CdS Magic-Size Clusters Assisted by Adding Small Molecules with Carboxylic Group

Reeling them in: Ph2PSiMe3 in the sequential formation of InP magic-sized clusters

Indium phosphide magic-sized clusters (MSCs) have been identified as a key step in the growth of InP quantum dots (QDs). However, the need for elevated temperatures to form QDs from MSCs has limited our understanding of this transformation. Herein, we utilize Ph₂PSiMe₃ to identify additional MSC intermediate species, which absorb from 365 nm to 490 nm. Excitingly, particle growth was carried out at 100 °C without the use of acidic surfactants. We show that despite being discrete, stable, and isolable sizes of MSCs, they form a reaction continuum, thus providing further insight into the growth mechanism of InP.

Size matters: Steric hindrance of precursor molecules controlling the evolution of CdSe magic-size clusters and quantum dots

Little is known about how to precisely promote the selective production of either colloidal semiconductor metal chalcogenide (ME), magic-size clusters (MSCs), or quantum dots (QDs). Recently, a two-pathway model has been proposed to comprehend their evolution; here, we reveal for the first time that the size of precursors plays a decisive role in the selected evolution pathway of MSCs and QDs. With the reaction of cadmium myristate (Cd(MA)₂) and tri-n-octylphosphine selenide (SeTOP) in 1-octadecene (ODE) as a model system, the size of Cd precursors was manipulated by the steric hindrance of carboxylic acid (RCOOH) additive. Without RCOOH, the reaction produced both CdSe MSCs and QDs (from 100 to 240 °C). With RCOOH, the reaction produced MSCs or QDs when R was small (such as CH₃-) or large (such as C₆H₅-), respectively. According to the two-pathway model, the selective evolution is attributed to the promotion and suppression of the self-assembly of Cd and Se precursors, respectively. We propose that the addition of carboxylic acid may occur ligand exchange with Cd(MA)₂, causing the different sizes of Cd precursor. The results suggest that the size of Cd precursors regulates the self-assemble behavior of the precursors, which dictates the directed evolution of either MSCs or QDs. The present findings bring insights into the two-pathway model, as the size of M and E precursors determine the evolution pathways of MSCs or QDs, the understanding of which is of great fundamental significance toward mechanism-enabled design and predictive synthesis of functional nanomaterials.

Electronic Supplementary Material

Supplementary material (additional optical absorption spectra, TEM, NMR, FT-IR, and XRD) is available in the online version of this article at 10.1007/s12274-022-4421-4.