Formation of ZnSe magic-size clusters displaying optical absorption doublets from prenucleation clusters

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).