Control of the Redox Activity of PbS Quantum Dots by Tuning Electrostatic Interactions at the Quantum Dot/Solvent Interface

Abstract

This paper describes the control of electron exchange between a colloidal PbS quantum dot (QD) and a negatively charged small molecule (9,10-anthraquinone-2-sulfonic acid sodium salt, AQ), through tuning of the charge density in the ligand shell of the QD, within an aqueous dispersion. The probability of electron exchange, measured through steady-state and time-resolved optical spectroscopy, is directly related to the permeability of the protective ligand shell, which is a mixed monolayer of negatively charged 6-mercaptohexanoate (MHA) and neutral 6-mercaptohexanol (MHO), to AQ. The composition of the ligand shell is quantitatively characterized by (1)H NMR. The dependence of the change in Gibbs free energy, ΔGobs, for the diffusion of AQ through the charged ligand shell and its subsequent adsorption to the QD surface is well-described with an electrostatic double-layer model for the QD/solvent interface. Fits of the optical data to this model yield an increase in the free energy for transfer of AQ from bulk solution to the surface of the QD (where it exchanges electrons with the QD) of 154 J/mol upon introduction of each additional charged MHA ligand to the ligand shell. This work expands the set of chemical parameters useful for controlling the redox activity of QDs via surface modification and suggests strategies for the use of nanoparticles for molecular and biomolecular recognition within chemically complex environments and for design of chemically stable nanoparticles for aqueous photocatalytic systems.

Quantum Dot–Peptide–Fullerene Bioconjugates for Visualization of in Vitro and in Vivo Cellular Membrane Potential

“…The Weiss group made similar observations in their studies of electron exchange between PbSe QDs and a negatively charged anthraquinone where the introduction of increasing numbers of charged 6-mercaptohexanoate ligands resulted in a concomitant decrease in the rate of ET. 92 …”

Quantum Dot Assembly for Light‐Driven Multielectron Redox Reactions, such as Hydrogen Evolution and CO2 Reduction

“…Unlike molecular dyes (e.g., Rhodamine, [18] Pt complexes [19] ), semiconductor QDs have al arge surface-tovolume ratio.This property enables QDs to expose abundant vacant surface sites for binding external cocatalysts.B inding cocatalysts that were originally diffusing in solution onto the QD surface greatly shortens their mutual distance,where d is much shorter than r (Figure 2a). Thec lose distance makes ultra-fast (often in at ime scale of picosecond, ps) [20] and consecutive electron injection from QDs to cocatalysts kinetically feasible.C ompared with diffusion-controlled systems, [21] the photo-induced electron transfer in systems with interface-directed assembly is dramatically facilitated allow-ing multiple redox equivalents to accumulate at active sites, thus favoring subsequent multielectron redox reactions.…”

Quantum Dot Assembly for Light‐Driven Multielectron Redox Reactions, such as Hydrogen Evolution and CO2 Reduction

“…The close distance makes ultra‐fast (often in a time scale of picosecond, ps) and consecutive electron injection from QDs to cocatalysts kinetically feasible. Compared with diffusion‐controlled systems, the photo‐induced electron transfer in systems with interface‐directed assembly is dramatically facilitated allowing multiple redox equivalents to accumulate at active sites, thus favoring subsequent multielectron redox reactions.…”