Hole Transfer from Photoexcited Quantum Dots: The Relationship between Driving Force and Rate

Abstract

We have investigated the relationship between driving force and rate for interfacial hole transfer from quantum dots (QDs). This relationship is experimentally explored by using six distinct molecular hole acceptors with an 800 meV range in driving force. Specifically, we have investigated ferrocene derivatives with alkyl thiol moieties that strongly bind to the surface of cadmium chalcogenide QDs. The redox potentials of these ligands are controlled by functionalization of the cyclopentadiene rings on ferrocene with electron withdrawing and donating substituents, thus providing an avenue for tuning the driving force for hole transfer while holding all other system parameters constant. The relative hole transfer rate constant from photoexcited CdSe/CdS core/shell QDs to tethered ferrocene derivatives is determined by measuring the photoluminescence quantum yield of these QD–molecular conjugates at varying ferrocene coverage, as determined via quantitative NMR. The resulting relationship between rate and energetic driving force for hole transfer is not well modeled by the standard two-state Marcus model, since no inverted region is observed. Alternative mechanisms for charge transfer are posited, including an Auger-assisted mechanism that provides a successful fit to the results. The observed relationship can be used to design QD–molecular systems that maximize interfacial charge transfer rates while minimizing energetic losses associated with the driving force.

Hydrogen Generation through Solar Photocatalytic Processes: A Review of the Configuration and the Properties of Effective Metal-Based Semiconductor Nanomaterials

“…A high specific area would increase not only the number of active catalytic sites, but also the number of superficial defect sites, which promote the recombination of free charge carriers [139]. For example, it has been reported that a high surface area for metal chalcogenides promotes the recombination processes through a "non-radiative" decay [140]. On the contrary, other studies demonstrated that an increase in the surface area of nanostructured titania does not generate an enhancement of the recombination rate of photogenerated charges [141].…”

Bridging Energetics and Dynamics of Exciton Trapping in Core–Shell Quantum Dots

“…[19][20] Furthermore, as recently discovered, the enhancement of Auger interactions in surface charged QDs causes non-Marcus behavior in charge-transfer processes. 15,[21][22] Depending on the application, all these photo-physical processes can be either useful or detrimental. A rational development of nanostructures, with tailored trapping, is crucial in view of their practical application.…”

Complementary Lock‐and‐Key Ligand Binding of a Triplet Transmitter to a Nanocrystal Photosensitizer

“…F TET(TA) was extracted from the kinetics at 445 nm of the CdSe/PyAn complexes after accounting for the contribution of the NC (Figure 3; see also Figure S8). [7,20] Another way of calculating the quantum efficiency of TET is by considering the photon upconversion QY obtained under CW irradiation, which is aconvolution of the following factors in Equation (3). In addition, the 2,2-PyAn transmitter with the lowest upconversion QY has the lowest F TET(TA) .H owever, we noticed that 2,2-PyAn quenches the CdSe NC donor more effectively than the 3,3-PyAn isomer (Figure 2c and Table 1) despite the fact that it has alower F TET(TA) and upconversion QY.T his observation is consistent with reports on the superlinear dependence of NC emission on ligand functionalization, and that NC photoluminescence can only be related to ligand binding at high surface coverage,and not at the low density of transmitter ligands in this work.…”