Bright, stable, and monodisperse colloidal semiconductor nanocrystals, or quantum dots (QDs), are typically synthesized in organic solvents. These synthesis protocols produce QDs with organic ligand shells, which render them insoluble in aqueous environments. Post-synthetic ligand exchange procedures replace organic ligands with water-soluble ligands, such as mercaptoalkanoic acids, and allow QDs originally synthesized in organic solvents to be dispersed in water. Despite the widespread use of these phase transfer procedures, their effects on QDs are poorly understood. Herein, we investigate the effects of phase transfer procedures on the photoluminescence (PL) of aqueous mercaptoalkanoic acid-capped lead sulfide (PbS) QDs. We report a bathochromic shift of the PL of PbS QD ensembles as a function of solution pH. The magnitude of the PL spectrum shift correlates with the polydispersity of the ensembles after phase transfer into water. The results of spectroscopic and scattering experiments, along with interparticle interaction calculations and computer simulations, suggest that the bathochromic shifts are the result of energy transfer within PbS QD assemblies that form as the solution pH decreases. This system is a model for spectroscopically monitoring the success, quality, and reproducibility of phase transfer procedures, which are critically important for producing high-quality aqueous QDs for applications in photocatalysis and biological sensing.<br/>

Investigating the effects of phase transfer procedures on the photoluminescence of aqueous quantum dots

2019 Spring National Meeting

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