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. 2023 Nov 7;23(22):10221–10227. doi: 10.1021/acs.nanolett.3c02749

Efficient Hole Transfer from CdSe Quantum Dots Enabled by Oxygen-Deficient Polyoxovanadate-Alkoxide Clusters

Nicole M B Cogan †, Kevin P McClelland †, Chari Y M Peter †, Chayan Carmenate Rodríguez †, Alex A Fertig †, Mitesh Amin †, William W Brennessel †, Todd D Krauss †,‡,*, Ellen M Matson †,*
PMCID: PMC10683070  PMID: 37935022

Abstract

graphic file with name nl3c02749_0005.jpg

A limitation of the implementation of cadmium chalcogenide quantum dots (QDs) in charge transfer systems is the efficient removal of photogenerated holes. Rapid hole transfer has typically required the ex situ functionalization of hole acceptors with groups that can coordinate to the surface of the QD. In addition to being synthetically limiting, this strategy also necessitates a competitive binding equilibrium between the hole acceptor and native, solubilizing ligands on the nanocrystal. Here we show that the incorporation of oxygen vacancies into polyoxovanadate-alkoxide clusters improves hole transfer kinetics by promoting surface interactions between the metal oxide assembly and the QD. Investigating the reactivity of oxygen-deficient clusters with phosphonate-capped QDs reveals reversible complexation of the POV-alkoxide with a phosphonate ligand at the nanocrystal surface. These findings reveal a new method of facilitating QD–hole acceptor association that bypasses the restrictions of exchange interactions.

Keywords: colloidal semiconductor nanocrystals, polyoxovanadate clusters, hole transfer, photoluminescence quenching

Cadmium chalcogenide (CdE; E = S, Se, or Te) semiconductor nanocrystals, or quantum dots (QDs), have attracted a great deal of attention as light-harvesting materials for photocatalysis due to their size-dependent bandgaps, high photostability, and large absorption cross sections compared to those of molecular chromophores.1 However, the implementation of QDs in photocatalytic systems requires the efficient separation and removal of charges in photogenerated excitons (i.e., dissociation of electron–hole pairs). While the extraction of electrons from the conduction band of photoexcited QDs has been extensively studied, efficient strategies for the transfer of holes remain underdeveloped.2−4 Indeed, reductive quenching of cadmium chalcogenide QDs has been identified as a significant barrier in optimizing the efficiency of these materials, given the inherently slow rate of hole transfer and the tendency for trapped holes to etch the nanoparticle surface or decrease colloidal stability through ligand oxidation.4−6

Recent work has highlighted strategies for enhancing the rate of hole transfer from CdE QDs.4,7 A key design consideration for facilitating charge transfer is association between the QD and the quencher through functionalization of the hole acceptor with a group capable of binding to the surface of the CdE nanocrystal.8 However, the binding groups of the quencher are often in competition with coordination of ligands used to solubilize QDs, requiring an additional ligand dissociation step or the addition of large excesses of a quencher. In addition, these functional groups can act as a thermodynamic barrier, inhibiting charge transfer.9 To remove this barrier, QD surface capping ligands have been developed that extend the wave function of the nanocrystal outside of the inorganic core and improve the rates of hole transfer to covalently bonded hole acceptors.10−13 Others have also shown that efficient hole transfer from CdSe QDs can be achieved through attachment to a hole-accepting scaffold, such as doped V2O5.14 We note, however, that a system that efficiently removes holes from CdE QDs without requiring an intricate organic synthesis or sacrificing the colloidal stability of the QDs is something that remains highly desirable.

Our research team is investigating molecular vanadium oxide assemblies as homogeneous hole acceptors for CdSe quantum dots. These polyoxovanadate-alkoxide (POV-alkoxide) clusters are composed of six vanadyl moieties arranged in a Lindqvist architecture.15 Substitution of surface bridging oxides with alkoxide ligands influences the physicochemical properties of the assembly; in addition to solubilizing the vanadium oxide core in an organic solvent,16−18 the ligands stabilize vanadium(IV) ions within the Lindqvist ion,15,19 rendering electron density available for the reductive quenching of photoexcited CdSe QDs. In previous work, we demonstrated that the addition of [V6O7(OEt)12]− to glutathione-capped CdSe QDs in a 1:1 mixture of ethanol and water enhanced the production of hydrogen from protons.20 After determining that the clusters do not function as proton reduction catalysts, we posed the question that catalytic enhancement was a result of an increased level of hole shuttling by the reduced POV-alkoxide. Unfortunately, we were unable to investigate hole transfer dynamics through steady-state or time-resolved photoluminescence (PL) spectroscopies, as [V6O7(OEt)12]− is also capable of accepting electrons from photoexcited CdSe QDs {[VIV5VVO7(OEt)12]− + e– → [VIV6O7(OEt)12]2–; E1/2 = −0.70 V vs NHE in dichloromethane}, complicating analysis.21

To exclusively interrogate hole transfer, we needed a form of the POV-alkoxide cluster that would eliminate the possibility of electron transfer from the CdSe QD. Unfortunately, the use of the POV-alkoxide cluster in its fully reduced charge state {e.g., [VIV6O7(OR)12]2–} was precluded by its poor solubility in nonpolar solvents. Our group has previously reported the synthesis of an oxygen-deficient variant of the Lindqvist ion, [V6O6(OMe)12]− (V6O6–), that is soluble in dichloromethane.22,23 The removal of an oxygen atom from the surface of parent assembly [V6O7(OMe)12]− (V6O7–) reduces a vanadium(V) center by two electrons, resulting in an oxidation-state distribution of vanadium centers of VIIIVIV5. Notably, electrochemical characterization of V6O6– reveals that the addition of further reducing equivalents to the cluster core is prohibited at energies relevant to electron transfer in CdSe QDs (Figures S1 and S4 and Table S1).24

Initial experiments focused on the steady-state analysis of charge transfer between tetradecylphosphonic acid (TDPA)-capped CdSe QDs and V6O6– (Figure 1a,c). Remarkably, we found that V6O6– quenches the fluorescence of the QDs at a nearly unity efficiency; upon addition of 0.5 equiv of V6O6– to a solution of TDPA-capped CdSe QDs in dichloromethane, the PL intensity is decreased by ∼50%, suggesting that nearly every added cluster quenches a corresponding QD. While comparable quenching efficiencies have been observed for statically bound, electron transfer systems,25 this amount of quenching is exceptional for a hole transfer system. Even in systems that leverage delocalizing ligands to accelerate hole transfer from the QD core, the addition of 100 equiv of a hole acceptor, resulting in 50 bound equivalents, is necessary to achieve >95% PL quenching.10 In contrast, our system can achieve a similar degree of charge transfer with only 10 equiv of V6O6–, total (Table S2).

Figure 1.

Figure 1

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(A) Normalized PL intensity and (B) normalized PL kinetics of CdSe-TDPA QDs with an increasing number of V6O6– equivalents. White dotted lines denote the fits using the corresponding parameters listed in Table S2. (C) Concentration-dependent behavior of steady-state PL quenching (red) and changes in PL lifetimes (black). The black dotted line is a guide to the eye, while the red dotted line is a linear fit. τ0 is the amplitude-weighted average PL lifetime of just the QDs, and τ is the lifetime with added V6O6– (see Table S2). (D) PL quenching efficiency based on steady-state EHT(quenching) (red) and time-resolved EHT(lifetimes) (red) measurements and calculated average numbers of acceptors per QD (black, Table S2), which are related to the number of equivalents of V6O6–. Error bars are estimated by the standard deviation of multiple measurements. EHT(quenching) is defined as 1 – I/I0, and EHT(lifetimes) is defined according to eq 5.32

Intrigued by the efficient quenching by V6O6–, we set out to identify the nature of interactions between the nanocrystal and redox mediator using a combination of steady-state and time-resolved fluorescence quenching studies. The steady-state PL quenching linearly depends on the concentration of V6O6–, which is typical for such Stern–Volmer analyses, whereby the dotted red line in Figure 1c is a fit to the equation I0/I = 1 + K[V6O6–], where K represents a quenching constant. Using time-correlated single-photon counting techniques (TCSPC) (Figure 1b), we found that with an increasing cluster concentration, the average lifetime of fluorescence for the QDs decreases, suggesting that V6O6– participates in dynamic charge transfer with CdSe QDs.8,26 Interestingly, we notice that the Stern–Volmer plot obtained from time-resolved PL spectroscopy shows saturation behavior with an increasing number of equivalents of clusters (Figure 1c). This saturation behavior is consistent with a heterogeneous QD–cluster population, which we propose contains weakly associated QD–cluster pairs (but still strongly quenching often termed static quenching), and also free clusters exhibiting weaker dynamic quenching of QD PL.26 The weaker dynamic quenching population leads to the expected linear change in PL lifetime with the added cluster, while for the QD–cluster adduct, the nonradiative rate is significantly large such that these QDs are effectively dark. Because dark QDs do not contribute PL photons to the time-resolved PL decay measurement, the τ0/τ ratio saturates while the PL quenching linearly increases with added cluster.27

The finding that V6O6– clusters and QDs are associating is significant, as a key factor facilitating oxidative charge transfer between CdSe QDs and molecular substrates is the ability of the hole acceptor to bind to the surface of the nanocrystal. However, unlike previously reported systems, these clusters do not contain functional groups that would promote the strong binding of the cluster to the surface of the nanocrystal. Indeed, the linear steady-state Stern–Volmer data (Figure 1c) suggest that static quenching arising from a strongly bound QD-cluster adduct is not occurring.26

PL quenching could arise from some combination of electron, hole, and energy transfer from the QD to the V6O6– cluster. Electron transfer is not expected because the cluster is unable to be reduced by a photoexcited electron on the QD (Figure S1). Nonetheless, we performed ultrafast transient absorption (TA) spectroscopy to probe the excited-state dynamics (see the Supporting Information for experimental details). Note that for core CdSe QDs, with the probe energy set to match the 1Se–1Sh3/2 exciton absorption, TA measurements measure almost exclusively electron dynamics and thus are not sensitive to hole dynamics.28,29 Therefore, we expected to see little change in the TA bleach decay dynamics as increasing amounts of the cluster were added. Indeed, the dynamics of the transient bleach over tens of picoseconds for the 1Se–1Sh3/2 exciton is very similar in the presence or absence of cluster (Figure 2). Note that if electron transfer were the operative mode of PL quenching, we would expect to see a significant decay in the TA bleach signal on these time scales, as we have observed for electron transfer to freely diffusing photocatalysts.30,31 Energy transfer can also be eliminated as the dominant quenching pathway on the basis of the low degree of spectral overlap between the QD donor and the V6O6– acceptor (Figure S2; see the Supporting Information for details of the estimate of a 20% upper bound for energy transfer-related quenching). At longer probe delay times approaching 1 ns, we do see some deviations in the TA signals from pure QDs as 1 and 10 equiv of cluster are added (Figure S3). These differences could be caused by oxidation of the V6O6– cluster to V6O7– during the TA measurement (thereby allowing for electron transfer to the cluster) and/or some contribution from energy transfer. Importantly, the magnitude of the difference does not nearly account for the amount of quenching that we observe. For example, at 10 equiv of cluster to QD the PL is almost completely quenched [by 90–98% (Table S2)], while the TA data suggest an upper bound on the possible loss of electron population by a factor of ∼2 (Figure S3).

Figure 2.

Figure 2

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Normalized change in transmission (ΔT) of the 1Se–1Sh3/2 transition CdSe QDs without V6O6– present (black) and with an increasing concentration of V6O6– as a function of probe delay.

To assess the effectiveness of the V6O6– clusters to quench QD PL, we modeled the average number of V6O7– per QD as described by Tachiya et al. using a Poissonian distribution:32

graphic file with name nl3c02749_m001.jpg 1

where fn is the probability of a given QD being quenched by nV6O6– cluster molecules and m = ⟨n⟩.28,30,32−39 The total rate of hole transfer is simply the product of the effective number of V6O6– clusters per QD (n) and the hole transfer rate for one cluster per QD:

graphic file with name nl3c02749_m002.jpg 2

Altogether, the PL decay of excited QDs at delay time t is given by

graphic file with name nl3c02749_m003.jpg 3

where I0 is a normalization constant corresponding to the initial concentration of excited QDs and Ai is the amplitude of the ith component of the QD PL decay without a cluster. It can then be shown that the right sum in eq 3 can be simplified resulting in32

graphic file with name nl3c02749_m004.jpg 4

The TCSPC PL decay dynamics were fitted using eq 4 to obtain the effective number of V6O6– clusters per QD and the HT rate of the 1:1 V6O6– to the QD system (see the Supporting Information for a description of the fitting process). The intrinsic QD PL decay is described by a triple-exponential function with the corresponding amplitudes and time constants listed in Table S2. We found that the HT process that arises upon the addition of V6O6– to the CdSe QDs system fits to a single exponential with a HT lifetime of 1.4 ns for the 1:1 catalyst:QD system. The amplitudes Bj, time constants τHTi (τHTi = 1/kHTi), and average number of cluster acceptors per QD, m, for the varying V6O6– cluster concentrations are also listed in Table S2. Consistent with the steady-state PL quenching data (Figure 1a), at only 0.5 equiv of V6O6–, m was determined to be 0.83, which suggests that nearly every added cluster is serving to quench PL from a QD (Figure 1d). In addition, while m increases monotonically with V6O6– concentration, the ability of the added cluster to quench QDs rapidly saturates, plateauing at m ∼ 2 for 10 equiv V6O6–. Additionally, the overall HT efficiency (EHT) can be estimated by taking the ratio of the integrated area under the time-resolved PL decay curves with and without the cluster according to40,41

graphic file with name nl3c02749_m005.jpg 5

because the integrated areas of the kinetic decays are proportional to the QD excited electron population. As shown in Figure 1d (and Table S2), the HT efficiency (EHT) is determined to be 56% for only 0.5 equiv of V6O6– and saturates at higher cluster concentrations at EHT ∼ 90%. As also shown in Figure 1d, EHT is consistent with the PL quenching yield, as determined by the steady-state PL quenching. Note that consistent with Figure 1c, EHT(quenching) > EHT(lifetimes) with any number of equivalents of V6O6–.

To identify the mechanism for this QD–cluster association, we next investigated the impact of cluster structure on charge transfer [Figure 3 and Figure S4; all potentials derived from literature or experimentally measured values (Table S1)]. We first compared steady-state PL quenching data of the fully oxygenated assembly, [V6O7(OMe)12]− (V6O7–), which resulted in a drastic reduction in the quenching efficiency compared to that of V6O6– (Figure 3c and Figure S5). The inefficient quenching of CdSe QDs by V6O7– strongly suggests that charge transfer to V6O6– benefits from some type of coordination mechanism accessed by the defect at the surface of the cluster. To validate the importance of the O-atom vacancy on association with the surface of the QD, we investigated charge transfer dynamics between CdSe QDs and an oxygen-deficient POV-alkoxide cluster functionalized with a 4-tert-butylcalix[4]arene (calix) ligand, [nBu4N][(calix)V6O6(OMe)8] [(calix)V6O6– (Figure 3a and Figure S6)].42 This cluster was selected as access to the O-atom vacancy is heavily restricted due to the steric bulk of the calix ligand, prohibiting direct interactions between the surface of the CdSe QD and the defect site. Indeed, fluorescence data in the presence of (calix)V6O6– show a quenching efficiency much lower than that with V6O6– (Figure 3c), supporting the hypothesis that the strong association observed in the case of V6O6– is caused by interaction between the O atom vacancy and the surface of the QD.

Figure 3.

Figure 3

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(A) Molecular structures and oxidation-state distributions of the metal ions of V6O6– and (calix)V6O6–. (B and C) Stern–Volmer plots for V6O6– (red), V6O7– (orange), and (calix)V6O6– (blue) clusters. All potentials are referenced against ferrocene in DCM. All quenching experiments were performed with 1 μM CdSe-TDPA QDs in DCM under inert gas.

Two potential modes of interaction between the TDPA-capped CdSe QDs and the vacancy of V6O6– clusters can be envisaged: (i) direct binding of the vacancy to surface Se atoms or (ii) association with TDPA ligands bound to the surface of the QD. Direct coordination to surface selenide moieties was discredited by the lack of reactivity of V6O6– with trimethylphosphine selenide (Figure S7); the soft character of selenide renders this Lewis base unreactive with the oxygen-deficient site of the POV-alkoxide. To evaluate the importance of surface ligand identity for cluster adhesion, we synthesized QDs of a similar size that were capped with oleic acid (OA) instead of TDPA. Steady-state PL quenching experiments with OA-capped CdSe and V6O6– clusters (Figure S8) show a charge transfer efficiency much weaker than that with TDPA-capped CdSe, indicating that the presence of TDPA is important for the association of V6O6– with the surface of the QD.

Given the result that the binding mechanism of V6O6– is mediated by the ligand, we hypothesized that the exposed vanadium center interacts directly with the “P=O” moiety of TDPA. This hypothesis was based on our previously reported finding of the coordination of alkyl phosphine oxide compounds to the coordinatively unsaturated vanadium center in oxygen-deficient POV-alkoxides.43 To probe the validity of this hypothesis, we next explored the reactivity of V6O6– with a phosphonate ester as a surrogate of QD-bound TDPA. Selection of the phosphonate ester eliminates potential reactivity with the acidic protons of the phosphonic acid, which are not expected in a phosphonate ligand bound to the QD surface.44 Addition of 2 equiv of dimethoxymethyl phosphine oxide [OPMe(OMe)2] to V6O6– in dichloromethane results in the instantaneous formation of a new species as observed by 1H NMR spectroscopy (Scheme 1 and Figure S9). Unambiguous determination of the molecular structure of V6O6(OPR3)– was obtained via single-crystal X-ray diffraction; refinement of the data reveals coordination of the phosphate ester to V6O6– occurs via binding of the phosphine oxide moiety of the ligand to the oxygen-deficient vanadium center (Figure S10 and Table S3). Notably, electrochemical characterization of V6O6(OPMe(OMe)2)– shows an electrochemical profile similar to that of V6O6–; no additional reduction events are accessible following coordination of the phosphine oxide moiety (Figure S1), indicating that hole transfer remains the sole charge transfer mechanism available upon complexation of the cluster to the TDPA ligands of the QD.

Scheme 1. Synthesis of V6O6(OPR3)–

Scheme 1

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Quantitative conversion of V6O6– into V6O6(OPMe(OMe)2)– following the addition of only 2 equiv of phosphate ester in dichloromethane is significant for understanding the near unity quenching of CdSe QDs by the oxygen-deficient POV-alkoxide. As this number is significantly lower than the expected number of phosphonate ligands required to keep the QDs colloidally stable (∼102),45 we can infer a strong association of V6O6– with TDPA-capped QDs at concentrations studied in this report. We hypothesize that binding of the ligand to the CdSe-QD remains unchanged upon introduction of the cluster; the bidentate nature of the phosphonate ligands leaves P=O functional groups accessible to complexation with V6O6–. Quantitative formation of a phosphonate ester adduct of the oxygen-deficient POV-alkoxide cluster is also observed when using a bulkier phosphonate ester [e.g., OPnBu(OnBu)2 (Figure S11)], suggesting that the sterics of the components bound to the phosphonate ligand do not have a substantial impact on the affinity of the phosphine oxide moiety of V6O6–.

The ligand-based association mechanism reported here is interesting, as most binding interactions with the surface of a QD require the ex situ functionalization of a binding group to a quencher followed by a competitive exchange interaction between the substrate and ligands.10 As phosphonate ligands form a very stable interaction with the surface of the QD, CdSe-TDPA nanocrystals would normally require an even stronger-binding, thiolate-functionalized quencher to displace the native ligands.46 However, thiolates are not appropriate for hole transfer systems as they participate in competitive, irreversible oxidation reactions.4Ex situ functionalization therefore requires either treatment of the CdSe-TDPA QDs to remove ligands or addition of excess equivalents of the preassociated TDPA-V6O6– complex to facilitate cluster association.47 The novel in situ binding mechanism presented here circumvents these issues by association with already bound ligands rather than their replacement, resulting in a nearly unity quenching efficiency.

Conclusion

We have shown that oxygen-deficient POV-alkoxides are effective redox mediators for the removal of photogenerated holes from CdSe QDs. We confirmed this through steady-state and time-resolved PL quenching studies of fully reduced clusters where hole transfer is the only available quenching pathway. Introduction of an oxygen atom vacancy drastically improves hole transfer from CdSe QDs to nearly unity quenching efficiency. Interestingly, we conclude that rather than a direct mechanism of binding to surface atoms, these clusters can form a complex with the phosphonate capping ligands on the QDs. This ligand-based binding method of surface adhesion circumvents the limitations of classical competitive exchange mechanisms, resulting in high degrees of quenching at stochiometric cluster concentrations. Our findings, therefore, point to a novel association mechanism between QDs and POV-alkoxide redox mediators that has drastic implications for oxidative chemistry.

Acknowledgments

The authors acknowledge Dr. Eric Schreiber and Dr. Trevor Tumiel for their participation in early iterations of this study. This work was supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy, via Grant DE-SC0002106.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.3c02749.

  • Experimental procedures and details of curve fitting calculations, supporting CV, NMR, and optical spectroscopic data (PDF)

  • Structural data for V6O6(OPMe(OMe)2)− (CIF)

Author Contributions

⊥ N.M.B.C., K.P.M., and C.Y.M.P. contributed equally to this work.

The authors declare no competing financial interest.

Supplementary Material

nl3c02749_si_001.pdf (1.1MB, pdf)
nl3c02749_si_002.cif (1.4MB, cif)

References

  1. Burke R.; Bren K. L.; Krauss T. D. Semiconductor nanocrystal photocatalysis for the production of solar fuels. J. Chem. Phys. 2021, 154, 030901 10.1063/5.0032172. [DOI] [PubMed] [Google Scholar]
  2. Zhu H.; Yang Y.; Wu K.; Lian T. Charge Transfer Dynamics from Photoexcited Semiconductor Quantum Dots. Annu. Rev. Phys. Chem. 2016, 67, 259–281. 10.1146/annurev-physchem-040215-112128. [DOI] [PubMed] [Google Scholar]
  3. Kamat P. V.; Christians J. A.; Radich E. J. Quantum Dot Solar Cells: Hole Transfer as a Limiting Factor in Boosting the Photoconversion Efficiency. Langmuir 2014, 30, 5716–5725. 10.1021/la500555w. [DOI] [PubMed] [Google Scholar]
  4. Kodaimati M. S.; McClelland K. P.; He C.; Lian S.; Jiang Y.; Zhang Z.; Weiss E. A. Viewpoint: Challenges in Colloidal Photocatalysis and Some Strategies for Addressing Them. Inorg. Chem. 2018, 57, 3659–3670. 10.1021/acs.inorgchem.7b03182. [DOI] [PubMed] [Google Scholar]
  5. McClelland K. P.; Weiss E. A. Selective Photocatalytic Oxidation of Benzyl Alcohol to Benzaldehyde or C–C Coupled Products by Visible-Light-Absorbing Quantum Dots. ACS Appl. Energy Mater. 2019, 2, 92–96. 10.1021/acsaem.8b01652. [DOI] [Google Scholar]
  6. Zhu H.; Song N.; Lian T. Charging of Quantum Dots by Sulfide Redox Electrolytes Reduces Electron Injection Efficiency in Quantum Dot Sensitized Solar Cells. J. Am. Chem. Soc. 2013, 135, 11461–11464. 10.1021/ja405026x. [DOI] [PubMed] [Google Scholar]
  7. Hines D. A.; Kamat P. V. Recent Advances in Quantum Dot Surface Chemistry. ACS Appl. Mater. Int. 2014, 6, 3041–3057. 10.1021/am405196u. [DOI] [PubMed] [Google Scholar]
  8. Dutta P.; Beaulac R. Photoluminescence Quenching of Colloidal CdSe and CdTe Quantum Dots by Nitroxide Free Radicals. Chem. Mater. 2016, 28, 1076–1084. 10.1021/acs.chemmater.5b04423. [DOI] [Google Scholar]
  9. Ding T. X.; Olshansky J. H.; Leone S. R.; Alivisatos A. P. Efficiency of Hole Transfer from Photoexcited Quantum Dots to Covalently Linked Molecular Species. J. Am. Chem. Soc. 2015, 137, 2021–2029. 10.1021/ja512278a. [DOI] [PubMed] [Google Scholar]
  10. Lian S.; Weinberg D. J.; Harris R. D.; Kodaimati M. S.; Weiss E. A. Subpicosecond Photoinduced Hole Transfer from a CdS Quantum Dot to a Molecular Acceptor Bound Through an Exciton-Delocalizing Ligand. ACS Nano 2016, 10, 6372–6382. 10.1021/acsnano.6b02814. [DOI] [PubMed] [Google Scholar]
  11. Westmoreland D. E.; López-Arteaga R.; Weiss E. A. N-Heterocyclic Carbenes as Reversible Exciton-Delocalizing Ligands for Photoluminescent Quantum Dots. J. Am. Chem. Soc. 2020, 142, 2690–2696. 10.1021/jacs.9b13605. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Harris R. D.; Amin V. A.; Lau B.; Weiss E. A. Role of Interligand Coupling in Determining the Interfacial Electronic Structure of Colloidal CdS Quantum Dots. ACS Nano 2016, 10, 1395–1403. 10.1021/acsnano.5b06837. [DOI] [PubMed] [Google Scholar]
  13. La Croix A. D.; O’Hara A.; Reid K. R.; Orfield N. J.; Pantelides S. T.; Rosenthal S. J.; Macdonald J. E. Design of a Hole Trapping Ligand. Nano Lett. 2017, 17, 909–914. 10.1021/acs.nanolett.6b04213. [DOI] [PubMed] [Google Scholar]
  14. Andrews J. L.; Cho J.; Wangoh L.; Suwandaratne N.; Sheng A.; Chauhan S.; Nieto K.; Mohr A.; Kadassery K. J.; Popeil M. R.; et al. Hole Extraction by Design in Photocatalytic Architectures Interfacing CdSe Quantum Dots with Topochemically Stabilized Tin Vanadium Oxide. J. Am. Chem. Soc. 2018, 140, 17163–17174. 10.1021/jacs.8b09924. [DOI] [PubMed] [Google Scholar]
  15. Spandl J.; Daniel C.; Brüdgam I.; Hartl H. Synthesis and Structural Characterization of Redox-Active Dodecamethoxoheptaoxohexavanadium Clusters. Angew. Chem., Int. Ed. 2003, 42, 1163–1166. 10.1002/anie.200390306. [DOI] [PubMed] [Google Scholar]
  16. VanGelder L. E.; Kosswattaarachchi A. M.; Forrestel P. L.; Cook T. R.; Matson E. M. Polyoxovanadate-alkoxide clusters as multi-electron charge carriers for symmetric non-aqueous redox flow batteries. Chem. Sci. 2018, 9, 1692–1699. 10.1039/C7SC05295B. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Kosswattaarachchi A. M.; VanGelder L. E.; Nachtigall O.; Hazelnis J. P.; Brennessel W. W.; Matson E. M.; Cook T. R. Transport and Electron Transfer Kinetics of Polyoxovanadate-Alkoxide Clusters. J. Electrochem. Soc. 2019, 166, A464–A472. 10.1149/2.1351902jes. [DOI] [Google Scholar]
  18. VanGelder L. E.; Schreiber E.; Matson E. M. Physicochemical implications of alkoxide “mixing” in polyoxovanadium clusters for nonaqueous energy storage. J. Mater. Chem. A 2019, 7, 4893–4902. 10.1039/C8TA12306C. [DOI] [Google Scholar]
  19. Daniel C.; Hartl H. Neutral and Cationic VIV/VV Mixed-Valence Alkoxo-polyoxovanadium Clusters [V6O7(OR)12]n+ (R = – CH3, – C2H5): Structural, Cyclovoltammetric and IR-Spectroscopic Investigations on Mixed Valency in a Hexanuclear Core. J. Am. Chem. Soc. 2005, 127, 13978–13987. 10.1021/ja052902b. [DOI] [PubMed] [Google Scholar]
  20. Edwards E. H.; Fertig A. A.; McClelland K. P.; Meidenbauer M. T.; Chakraborty S.; Krauss T. D.; Bren K. L.; Matson E. M. Enhancing the activity of photocatalytic hydrogen evolution from CdSe quantum dots with a polyoxovanadate cluster. Chem. Commun. 2020, 56, 8762–8765. 10.1039/D0CC03163A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Inamdar S. N.; Ingole P. P.; Haram S. K. Determination of Band Structure Parameters and the Quasi-Particle Gap of CdSe Quantum Dots by Cyclic Voltammetry. ChemPhysChem 2008, 9, 2574–2579. 10.1002/cphc.200800482. [DOI] [PubMed] [Google Scholar]
  22. Petel B. E.; Brennessel W. W.; Matson E. M. Oxygen-Atom Vacancy Formation at Polyoxovanadate Clusters: Homogeneous Models for Reducible Metal Oxides. J. Am. Chem. Soc. 2018, 140, 8424–8428. 10.1021/jacs.8b05298. [DOI] [PubMed] [Google Scholar]
  23. Schreiber E.; Fertig A. A.; Brennessel W. W.; Matson E. M. Oxygen-Atom Defect Formation in Polyoxovanadate Clusters via Proton-Coupled Electron Transfer. J. Am. Chem. Soc. 2022, 144, 5029–5041. 10.1021/jacs.1c13432. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Jasieniak J.; Califano M.; Watkins S. E. Size-Dependent Valence and Conduction Band-Edge Energies of Semiconductor Nanocrystals. ACS Nano 2011, 5, 5888–5902. 10.1021/nn201681s. [DOI] [PubMed] [Google Scholar]
  25. Lian S.; Kodaimati M. S.; Dolzhnikov D. S.; Calzada R.; Weiss E. A. Powering a CO2 Reduction Catalyst with Visible Light through Multiple Sub-picosecond Electron Transfers from a Quantum Dot. J. Am. Chem. Soc. 2017, 139, 8931–8938. 10.1021/jacs.7b03134. [DOI] [PubMed] [Google Scholar]
  26. Lakowicz J. R., Ed. Dynamics of Solvent and Spectral Relaxation. In Principles of Fluorescence Spectroscopy; Springer US, 2006; pp 237–276. [Google Scholar]
  27. Genovese D.; Cingolani M.; Rampazzo E.; Prodi L.; Zaccheroni N. Static quenching upon adduct formation: a treatment without shortcuts and approximations. Chem. Soc. Rev. 2021, 50, 8414–8427. 10.1039/D1CS00422K. [DOI] [PubMed] [Google Scholar]
  28. Klimov V. I.; McBranch D. W.; Leatherdale C. A.; Bawendi M. G. Electron and hole relaxation pathways in semiconductor quantum dots. Phys. Rev. B 1999, 60, 13740–13749. 10.1103/PhysRevB.60.13740. [DOI] [Google Scholar]
  29. Klimov V. I.; Schwarz C. J.; McBranch D. W.; Leatherdale C. A.; Bawendi M. G. Ultrafast dynamics of inter- and intraband transitions in semiconductor nanocrystals: Implications for quantum-dot lasers. Phys. Rev. B 1999, 60, R2177–R2180. 10.1103/PhysRevB.60.R2177. [DOI] [Google Scholar]
  30. Burke R.; Cogan N. M. B.; Oi A.; Krauss T. D. Recovery of Active and Efficient Photocatalytic H2 Production for CdSe Quantum Dots. J. Phys. Chem. C 2018, 122, 14099–14106. 10.1021/acs.jpcc.8b01237. [DOI] [Google Scholar]
  31. Liu C.; Qiu F.; Peterson J. J.; Krauss T. D. Aqueous Photogeneration of H2 with CdSe Nanocrystals and Nickel Catalysts: Electron Transfer Dynamics. J. Phys. Chem. B 2015, 119, 7349–7357. 10.1021/jp510935w. [DOI] [PubMed] [Google Scholar]
  32. Sadhu S.; Tachiya M.; Patra A. A Stochastic Model for Energy Transfer from CdS Quantum Dots/Rods (Donors) to Nile Red Dye (Acceptors). J. Phys. Chem. C 2009, 113, 19488–19492. 10.1021/jp906160z. [DOI] [Google Scholar]
  33. Boulesbaa A.; Huang Z.; Wu D.; Lian T. Competition between Energy and Electron Transfer from CdSe QDs to Adsorbed Rhodamine B. J. Phys. Chem. C 2010, 114, 962–969. 10.1021/jp909972b. [DOI] [Google Scholar]
  34. Morris-Cohen A. J.; Frederick M. T.; Cass L. C.; Weiss E. A. Simultaneous Determination of the Adsorption Constant and the Photoinduced Electron Transfer Rate for a Cds Quantum Dot–Viologen Complex. J. Am. Chem. Soc. 2011, 133, 10146–10154. 10.1021/ja2010237. [DOI] [PubMed] [Google Scholar]
  35. Rodgers M. A. J.; Da Silva E Wheeler M. F. Quenching of Fluorescence from Pyrene in Micellar Solutions by Cationic Quenchers. Chem. Phys. Lett. 1978, 53, 165–169. 10.1016/0009-2614(78)80415-1. [DOI] [Google Scholar]
  36. Koole R.; Luigjes B.; Tachiya M.; Pool R.; Vlugt T. J. H.; de Mello Donegá C.; Meijerink A.; Vanmaekelbergh D. Differences in Cross-Link Chemistry between Rigid and Flexible Dithiol Molecules Revealed by Optical Studies of CdTe Quantum Dots. J. Phys. Chem. C 2007, 111, 11208–11215. 10.1021/jp072407x. [DOI] [Google Scholar]
  37. Huang J.; Huang Z.; Jin S.; Lian T. Exciton Dissociation in CdSe Quantum Dots by Hole Transfer to Phenothiazine. J. Phys. Chem. C 2008, 112, 19734–19738. 10.1021/jp808291u. [DOI] [Google Scholar]
  38. Peterson M. D.; Jensen S. C.; Weinberg D. J.; Weiss E. A. Mechanisms for Adsorption of Methyl Viologen on CdS Quantum Dots. ACS Nano 2014, 8, 2826–2837. 10.1021/nn406651a. [DOI] [PubMed] [Google Scholar]
  39. Tachiya M. Kinetics of quenching of luminescent probes in micellar systems. II. J. Chem. Phys. 1982, 76, 340–348. 10.1063/1.442728. [DOI] [Google Scholar]
  40. Lakowicz J. R.Principles of Fluorescence Spectroscopy; Kluwer Academic, 1999. [Google Scholar]
  41. Tseng H.-W.; Wilker M. B.; Damrauer N. H.; Dukovic G. Charge Transfer Dynamics between Photoexcited CdS Nanorods and Mononuclear Ru Water-Oxidation Catalysts. J. Am. Chem. Soc. 2013, 135 (9), 3383–3386. 10.1021/ja400178g. [DOI] [PubMed] [Google Scholar]
  42. Meyer R. L.; Miró P.; Brennessel W. W.; Matson E. M. O2 Activation with a Sterically Encumbered, Oxygen-Deficient Polyoxovanadate-Alkoxide Cluster. Inorg. Chem. 2021, 60, 13833–13843. 10.1021/acs.inorgchem.1c00887. [DOI] [PubMed] [Google Scholar]
  43. Petel B. E.; Meyer R. L.; Brennessel W. W.; Matson E. M. Oxygen atom transfer with organofunctionalized polyoxovanadium clusters: O-atom vacancy formation with tertiary phosphanes and deoxygenation of styrene oxide. Chemical Science 2019, 10, 8035–8045. 10.1039/C9SC02882J. [DOI] [PMC free article] [PubMed] [Google Scholar]
  44. García-Rodríguez R.; Hendricks M. P.; Cossairt B. M.; Liu H.; Owen J. S. Conversion Reactions of Cadmium Chalcogenide Nanocrystal Precursors. Chem. Mater. 2013, 25, 1233–1249. 10.1021/cm3035642. [DOI] [Google Scholar]
  45. Gomes R.; Hassinen A.; Szczygiel A.; Zhao Q.; Vantomme A.; Martins J. C.; Hens Z. Binding of Phosphonic Acids to CdSe Quantum Dots: A Solution NMR Study. J. Phys. Chem. Lett. 2011, 2, 145–152. 10.1021/jz1016729. [DOI] [Google Scholar]
  46. Knauf R. R.; Lennox J. C.; Dempsey J. L. Quantifying Ligand Exchange Reactions at CdSe Nanocrystal Surfaces. Chem. Mater. 2016, 28, 4762–4770. 10.1021/acs.chemmater.6b01827. [DOI] [Google Scholar]
  47. Owen J. S.; Park J.; Trudeau P.-E.; Alivisatos A. P. Reaction Chemistry and Ligand Exchange at Cadmium–Selenide Nanocrystal Surfaces. J. Am. Chem. Soc. 2008, 130, 12279–12281. 10.1021/ja804414f. [DOI] [PubMed] [Google Scholar]

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