The precursor compound of two types of ZnSe magic-sized clusters

Precursor compounds(PCs)link quantum dots(QDs)and magic-sized clusters(MSCs),which is pivotal in the conversion between QDs and MSCs.Here,for the first time,we report the transformation,synthesis,and composition of a type of ZnSe PCs.ZnSe PCs can be directly transformed to two different MSCs with the assistance of octylamine and acetic acid at room temperature.The two types of MSCs exhibit sharp absorption peaks at 299 and 328 nm which are denoted as MSC-299 and MSC-328.In the preparation of ZnSe PCs,diphenylphosphine(DPP)as an additive plays a key role which not only inhibits the thermal decomposition of Zn precursor,but also acts as a reducing agent to reduce the by-products produced in the reaction.The composition was explored by X-ray photoelectron spectroscopy,energy dispersive spectrometer,matrix-assisted laser desorption/ionization time-of-flight mass spectra with ZnSe PC powder appeared as white powder after purifying by toluene(Tol)and methanol(MeOH).The results indicate that the molar ratio of Zn/Se is 2:1 with a molecular of〜3,350 Da.Therefore,we propose that the molecular formula of ZnSe PCs is Zn_(32)Se_(16).In addition,at the molecular level,the covalent bond of Zn-Se is formed in ZnSe PCs.This study offers a deeper understanding of the transformation from PCs to MSCs and for the first time proposes the composition of PCs.Meanwhile,this research provides us with a new understanding of the role of DPP in the synthesis of colloidal semiconductor nanoparticles.

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℃).With RCOOH,the reaction produced MSCs or QDs when R was small(such as CH3−)or large(such as C6H5−),respectively.According to the twopathway 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.