Surface-Ligand Tuned Reversible Transformations in Aqueous Environments Between CdSe Magic-Size Clusters and Their Precursor Compounds

That magic-size clusters (MSCs) have their counterpart precursor compounds (PCs) has not been generally accepted by expertise circles. Here, experimental evidence to support this new concept is presented. With aqueous-phase CdSe MSCs as a model system, it is shown that when the MSCs are dispersed in water containing a certain amount of L-cysteine (Cys), the MSCs disappear slowly. Upon the addition of CdCl2, the MSCs recover. It is proposed that after dispersing, the MSCs transform to their quasi-isomeric, non-absorbing PCs upon Cys addition. In the presence of CdCl2, the PCs transform back to the MSCs due to Cys elimination. The surface ligand Cys of the MSCs plays a significant role in the reversible transformations. The present study provides compelling evidence that absorbing MSCs have their non-absorbing PCs. The study findings suggest that the transformation between two MSCs that display absorption spectral shifts in a stepwise pattern is assisted by their PCs. Reversible quasi-isomerizations between a l-cysteine (Cys)-passivated CdSe magic-size cluster (MSC) and its non-absorbing precursor compound (PC) are tuned by the change of surface ligand. The CdSe MSC has a ligand addition reaction in the presence of excess Cys, facilitating its transformation to PC. When the surrounding Cys molecules are consumed, the CdSe PC has a ligand elimination reaction, promoting its transformation to MSC.image