Spectroscopic Evidence in Optical Absorption for the Formation and Transformation of Prenucleation Clusters of CdS Quantum Dots

High Resolution Image Download MS PowerPoint Slide Prenucleation clusters (PNCs) that occupy a local minimum in the energy landscape have been suggested to form via chemical self-assembly prior to the nucleation and growth of colloidal semiconductor quantum dots (QDs) in reactions of individual cation and anion containing molecules. However, firm spectroscopic evidence for the PNC has previously proven elusive. Using two model reactions of cadmium oleate + 1-dodecanethiol and cadmium oleate + sulfur, we show the first signature signal of optical absorption between 260 and 290 nm for CdS PNCs. Controlling the PNC transformation into magic-size clusters (MSCs) in dispersion, we demonstrate a clear reciprocal relationship of the absorption strength between the PNC and the MSC. Our findings build a solid foundation for PNC formation in QD reactions and bring a deeper insight into the molecule–PNC–QD/MSC transition sequence, the knowledge of which enables the transformation of nanochemistry from an empirical art to a science.