Transformations Among Colloidal Semiconductor Magic-Size Clusters

Abstract

Conspectus A knowledge of colloidal semiconductor magic-size clusters (MSCs) is essential for understanding how fundamental properties evolve during transformations from individual molecules to semiconductor quantum dots (QDs). Compared to QDs, MSCs display much narrower optical absorption bands; the higher cluster stability gives rise to a narrower size distribution. During the production of binary QDs such as II–VI metal (M) chalcogenide (E) ones, binary ME MSCs observed were interpreted as side products and/or the nuclei of QDs. Prior to the current development of our two-step approach followed by our two-pathway model, it had been extremely challenging to synthesize MSCs as a unique product without the nucleation and growth of QDs. With the two-step approach, we have demonstrated that MSCs can be readily engineered as a sole product at room temperature from a prenucleation stage sample, also called an induction period (IP) sample. It is important that we were able to discover that the evolution of the MSCs follows first-order reaction kinetics behavior. Accordingly, we proposed that a new type of compound, termed as “precursor compounds” (PCs) of MSCs, was produced in an IP sample. Such PCs are optically transparent at the absorption peak positions of their MSC counterparts as well as to longer wavelengths. It is thought that quasi isomerization of a single PC results in the development of one MSC. In this Account, we provide an overview of our latest advances regarding the transformations among binary CdE MSCs as well as from binary CdTe to ternary CdTeSe MSCs. Optical absorption spectroscopy has been employed to study these transformations, all of which display well-defined isosbestic points. We have proposed that these MSC to MSC transformations occur via their corresponding PCs, also called immediate PCs. It is reasonable that the as-synthesized PC (in an IP sample) and the immediate PC (in an incubated and/or diluted sample) probably have different configurations. A transformation between two PCs may involve an intermolecular reaction, with either first-order reaction kinetics or a more complicated time profile. A transformation between one immediate PC and its counterpart MSC may contain an intramolecular reaction. The present Account, which addresses the PC-enabled MSC transformations with isosbestic points probed by optical absorption spectroscopy, calls for more experimental and theoretical attention to understand these magic species and their transformation processes more precisely.

Transformation Pathways in Colloidal CdTeSe Magic‐Size Clusters

“…It is established that colloidal semiconductor compound magic-size clusters (MSCs) have particular precursor compounds (PCs). [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Thef ormer (MSC-A) exhibits distinct optical absorption peaking at ac onstant wavelength A expressed in nanometers (nm), while the latter (PC-A) is usually transparent at this wavelength Aa nd to longer wavelengths.T he MSCs and their counterpart PCs are quasi isomers and transform mutually via reversible intramolecular reorganization. Furthermore,t he transformation between types of MSCs has been observed, [1][2][3][4][5][6][7][8][9][10] following ap athway that appears to be PC-enabled comprising three key steps (Scheme S1).…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Thef ormer (MSC-A) exhibits distinct optical absorption peaking at ac onstant wavelength A expressed in nanometers (nm), while the latter (PC-A) is usually transparent at this wavelength Aa nd to longer wavelengths.T he MSCs and their counterpart PCs are quasi isomers and transform mutually via reversible intramolecular reorganization. Furthermore,t he transformation between types of MSCs has been observed, [1][2][3][4][5][6][7][8][9][10] following ap athway that appears to be PC-enabled comprising three key steps (Scheme S1). ForaMSC-A to MSC-B transformation, the three steps are MSC-A to PC-A, PC-A to PC-B,and PC-B to MSC-B.However,the reported transformations are limited to those between two binary MSCs, [3][4][5][6][7][8][9][10] or between ab inary MSC and at ernary MSC.…”

Transformation Pathway from CdSe Magic‐Size Clusters with Absorption Doublets at 373/393 nm to Clusters at 434/460 nm

“…[52][53][54][55] We anticipate that the PC-enabled pathway (Scheme 1) has general applicability for transformations such as from PL CdSe dMSC-460 to dMSC-513, [36] as well as from PL CdTedMSC-427 to dMSC-495, to dMSC-550, and to dMSC-600. [31] Thepresent findings bring sophisticated insight into the pathway of the MSC evolution and transformation, the latter of which experiences reactions of monomer substitution [1] or addition that transform two MSC counterpart PCs.…”

“…At sufficiently high concentrations (a and b), the fragmentation of PC-393 enabled the dMSC-393 to dMSC-460 transformation (Scheme 1). At low concentrations (c), the fragmentation of PC-393 facilitated the nucleation and growth of conventional QDs (Scheme S1) [1,2].…”

Transformation Pathways in Colloidal CdTeSe Magic‐Size Clusters

“…Furthermore,t he transformation between types of MSCs has been observed, [1][2][3][4][5][6][7][8][9][10] following ap athway that appears to be PC-enabled comprising three key steps (Scheme S1). ForaMSC-A to MSC-B transformation, the three steps are MSC-A to PC-A, PC-A to PC-B,and PC-B to MSC-B.However,the reported transformations are limited to those between two binary MSCs, [3][4][5][6][7][8][9][10] or between ab inary MSC and at ernary MSC. [1,2,5] Before the present study, transformations in ternary MSCs have not been reported.…”