Direct Visualization of Ligands Exchange on the Surfaces of Quantum Dots by a Two-Phase Approach

摘要

Semiconductor quantum dots (QDs) have a wide range of applications owing to their uniquely photoelectric performance. It is helpful to modify QDs with desired polymer chains for improving their steric stabilization and compatibilization. Although various strategies have been successfully developed to graft polymer chains onto the surfaces of QDs, few methods can directly monitor the process of grafting. In this study, we took advantages of the color labels of QDs and developed a simple and convenient “grafting-to” method by ligand exchange, which occurred in a two-phase system with direct visualization. Briefly, cadmium selenide@cadmium sulphide core-shell QDs capped by n-trioctylphosphine oxide (TOPOCdSe@ CdS QDs), dispersed in n-hexane, and amino/thiol terminated polystyrene (PS-NH2/PS-SH), dissolved in N,N-dimethylformamide (DMF), were mixed to form a novel two-phase system. A direct visualization of the QDs from n-hexane to DMF confirmed the ligand exchange on the surfaces of QDs. Further evidences for the ligand exchange were provided by both Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (~1H NMR) studies, as well as by the grafting density of the PS on the surface of QDs. The PS-grafted QDs can improve the compatibility with the polymers chemically or structurally similar to PS, which makes them useful as functional additives in the polymer matrix to construct nanocomposites with desired optical and mechanical properties.