Near-Quantitative Yield for Transfer of Near-Infrared Excitons within Solution-Phase Assemblies of PbS Quantum Dots

Abstract

Covalent coupling of colloidal PbS quantum dots (QDs) of two different sizes through amide bond formation yielded assemblies that mediate near-infrared excitonic energy transfer from smaller QDs to larger QDs with 90% quantum yield, in chloroform solution. The energy transfer lifetimes, determined by fitting the kinetic data with a model that accounts for multiple hopping steps and different sizes of QD aggregates, were 113 ± 26 ns and 850 ± 330 ns, which compete favorably with intrinsic exciton decay in 600 ns to 2.5 μs. The high yield of energy transfer was accomplished by optimizing the sizes of the donor and acceptor QDs to maximize spectral overlap, the ratio of donor QDs to acceptor QDs, the coverage of "functional" ligand (8-amino-1-octanethiol on the donor QDs and 8-mercapto-1-octanoic acid on the acceptor QDs) on the QD surfaces, the amount of ethyl-dimethylaminopropylcarbodiimide (EDC) and N-hydroxy-succinimide (NHS) coupling reagents, the degree of steric hindrance for the amide coupling reaction, and the lengths of all involved ligands to maximize the solubility of small QD aggregates. Transmission electron microscopy images show coupling of donor and acceptor QDs into well-mixed heteroassemblies (dimers, trimers, and higher oligomers). The quantum yield for energy transfer was determined by comparing the enhancement of the photoluminescence intensity of acceptor PbS QDs with that of PbS QDs within energy transfer-inactive PbS QD−CdS QD "control" assemblies, which underwent the same chemical treatment as the PbS QD−PbS QD assemblies but do not have an available energy transfer pathway.

Energy transfer-enhanced photocatalytic reduction of protons within quantum dot light-harvesting–catalyst assemblies

“…Our conclusion that the enhancement of catalytic activity of the system is due to energy funneling is also supported by the agreement of our experimental data with the values of IQE and IQE cQD extracted from simulations of exciton dynamics in the QD assemblies using a master equation model (36,37,41) (Fig. 4 B and C, red), where EnT is the only interaction among QDs.…”

Distance-Dependence of Interparticle Energy Transfer in the Near-Infrared within Electrostatic Assemblies of PbS Quantum Dots

“…With decreasing “ n ”, the average interparticle (center-to-center) distance within the assemblies decreases from 5.8 nm to 3.7 nm, and the average time constant for EnT from donor (smaller) QDs to acceptor (larger) QDs increases from (∼150 ns) −1 to (2 ns) −1 . Our measured rate constant of (2 ns) −1 is not yet fast enough to outcompete the Auger process, but it is the fastest measured EnT rate between PbS QDs in film or solution. − While it has been assumed in the QD literature that the PDA is an adequate method to describe interparticle EnT in the near-IR, − we demonstrate that the PDA only sufficiently describes the EnT rate between PbS QDs for interparticle distances greater than 4 nm and drastically underestimates this rate for interparticle distances less than 4 nm (approximately the diameter of our chromophore). We significantly improve the accuracy of our calculations by replacing the PDA with a transition density cube (TDC) method for calculating Coulombic coupling between transition densities, which better accounts for the delocalization of the excited-state wave functions of the QDs throughout the volume of the particle.…”

Monte Carlo Evaluation of <i>In Vivo</i> Neuroimaging Using Quantum Dots with Fluorescence in the Second Window of Near Infrared Region

“…(ii) Quantum yield of quantum dots used in this study is unity. This is a good approximation for simple handling of the calculations because NIR-emitting quantum dots with high quantum yield (>90%) have been reported [8].…”