Spontaneous Patterning of Binary Ligand Mixtures on CdSe Nanocrystals: From Random to Janus Packing

Binary compositions of surface ligands are known to improve the colloidal stability and fluorescence quantum yield of nanocrystals (NCs), due to ligand-ligand interactions and surface organization. Herein, we follow the thermody-namics of a ligand exchange reaction of CdSe NCs with alkylthiol mixtures. The effects of ligand polarity and length difference on ligand packing were investigated using isothermal titration calorimetry (ITC). The thermodynamic signature of the formation of mixed ligand shells was observed. Correlating the experimental results with thermodynamic mixing models has allowed us to calculate the interchain interactions and to infer the final ligand shell configuration. Our findings demonstrate that, in contrast to macroscopic surfaces, the small dimensions of the NCs and the subsequent increased interfacial region between dissimilar ligands allow the formation of a myriad of clustering patterns, controlled by the interligand interactions. This work provides a fundamental understanding of the parameters determining the ligand shell structure and should help guide smart surface design toward NC-based applications.

Automated summary

Binary compositions of surface ligands significantly improve the colloidal stability and fluorescence quantum yield of nanocrystals (NCs). In this study, the thermodynamics of a ligand exchange reaction of CdSe NCs with alkylthiol mixtures were investigated using isothermal titration calorimetry (ITC). It was found that the interligand interactions determine the clustering patterns of the ligand shell structure. This work provides fundamental insights for the design of smart surfaces in NC-based applications.