Abstract
Structural isomerism of colloidal semiconductor nanocrystals has been largely unexplored. Here, we report one pair of structural isomers identified for colloidal nanocrystals which exhibit thermally-induced reversible transformations behaving like molecular isomerization. The two isomers are CdS magic-size clusters with sharp absorption peaks at 311 and 322 nm. They have identical cluster masses, but slightly different structures. Furthermore, their interconversions follow first-order unimolecular reaction kinetics. We anticipate that such isomeric kinetics are applicable to a variety of small-size functional nanomaterials, and that the methodology developed for our kinetic study will be helpful to investigate and exploit solid–solid transformations in other semiconductor nanocrystals. The findings on structural isomerism should stimulate attention toward advanced design and synthesis of functional nanomaterials enabled by structural transformations.
Highlights
Structural isomerism of colloidal semiconductor nanocrystals has been largely unexplored
We demonstrated that the evolution of CdS magic-size cluster (MSC)-311, referred to as the wavelength in nanometers of their absorption peak position, from their immediate precursors (IPs) followed first-order unimolecular reaction kinetics
We demonstrate that the MSCs are isomeric with the same cluster mass, but have slightly different structures based on matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS), X-ray total scattering with atomic pair distribution function (PDF) analysis, and small angle X-ray scattering (SAXS)
Summary
Structural isomerism of colloidal semiconductor nanocrystals has been largely unexplored. Their interconversions follow first-order unimolecular reaction kinetics We anticipate that such isomeric kinetics are applicable to a variety of small-size functional nanomaterials, and that the methodology developed for our kinetic study will be helpful to investigate and exploit solid–solid transformations in other semiconductor nanocrystals. Solid–solid transformations take place between two solid states[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19], with growing evidence for their applicability to colloidal semiconductor nanocrystals (NCs)[1,2,3,4]. The structural transformation from the IP to MSC-311 was attributed to the intramolecular reorganization caused by a proton-mediated ligand exchange[28,38], and was independent of the concentration of the IP and of the degree of supersaturation[28]
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