Little is known about the room-temperature formation of colloidal semiconductor magic-size clusters (MSCs) of II-VI ternary CdE₁E₂ from ZnE₁E₂. Here, we report the first synthesis of CdTeSe MSCs from ZnTeSe MSC-340 (displaying a sharp optical absorption peaking at 340 nm) at room temperature. When ZnTeSe MSC-340 and Cd(OAc)₂/OLA (made from cadmium acetate and oleylamine) were mixed, the former disappeared, while CdTeSe MSC-422 and/or MSC-399 developed. Based on our experimental data, we propose that the conversion proceeds via the interaction of Cd(OAc)₂/OLA and the precursor compound of ZnTeSe MSC-340, PC-340. As such, ZnTeSe MSC-340 first isomerized to PC-340; via cation exchange PC-340 transformed to CdTeSe PCs. In turn, the resultant CdTeSe PC isomerized to CdTeSe MSCs, the process of which was rate-determining. Furthermore, we show that the transformation between CdTeSe MSC-422 and MSC-399 was reversible, providing strong evidence that they are a pair of isomers. Our study introduces a room-temperature avenue towards Cd-based MSCs from Zn-based ones, which follows anionic framework conservation and anionic number conservation.

Cadmium selenide (CdSe) is a model system that has been widely used to study the synthesis of semiconductor magic-size clusters (MSCs) and quantum dots (QDs), together with their formation pathways, optical properties, and quantum confinement effects. Here, we show the occurrence of MSC-330, MSC-360, MSC-390, and MSC-415 from a prenucleation-stage sample of CdSe in dispersion at temperatures much lower than the sample preparation temperature. The number represents the lowest energy peak in nanometers of optical absorption. We develop a model based on prenucleation clusters (PNCs) to explain and rationalize our experimental data, and propose that the MSCs are a group of isomers emerging from their corresponding precursor compounds (PCs). The PNC−MSC-415 isomerization is driven thermodynamically, with the loss in enthalpy ( $\mathrm{\Delta }H$ < 0) and entropy ( $\mathrm{\Delta }S$ < 0). With that, we introduce a PNC-based approach to control the MSC development in dispersion, and provide compelling evidence for the existence of the PNC and of two categories of MSCs displaying either absorption singlets or doublets.

The formation pathway of colloidal semiconductor ZnSe magic-size clusters (MSCs) in a reaction that display an optical absorption doublet remains poorly understood. The reaction of Zn(OAc)₂/OLA (made from zinc acetate and oleylamine) and tri-n-octylphosphine selenide (SeTOP) in OLA in the presence of diphenylphosphine (HPPh₂) is studied, in which dMSC-345 displays a doublet peaking at 328/345 nm. We suggest that the development is from the clusters that form in the initial prenucleation stage of the reaction. The clusters are the precursor compound (PC-299) of MSC-299 (displaying an absorption singlet peaking at 299 nm). PC-299 transforms to PC-345 at a later stage. The presence of alcohol (such as methanol or ethylene glycol) promotes another pathway, which is the PC-299 to PC-320 transformation. PC-320 transforms to dMSC-320 (with a doublet at 305/320 nm), followed by dMSC-345 via PC-345. The present study provides additional evidence that clusters (PC-299) form and transform (such as to dMSC-345 via PC-345) in the prenucleation stage of ZnSe quantum dots (QDs).

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.