Ligand exchange of CdSe nanocrystals probed by optical spectroscopy in the visible and mid-IR

Holt, Birgit von; Kudera, Stefan; Weiß, Andreas; Schrader, Tobias E.; Manna, Liberato; Parak, Wolfgang J.; Braun, Markus

doi:10.1039/b720009a

Cited by 71 publications

(74 citation statements)

References 36 publications

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“…9-27 As a result, detailed studies have appeared that seek to understand the relationship between ligation and charge trapping. 6,28-40 However, models that adequately explain this behavior are lacking, and the precise relationship between PLQY and ligation largely remains a mystery.…”

Section: Introductionmentioning

confidence: 99%

Ligand Exchange and the Stoichiometry of Metal Chalcogenide Nanocrystals: Spectroscopic Observation of Facile Metal-Carboxylate Displacement and Binding

et al. 2013

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We demonstrate that metal carboxylate complexes (L–M(O2CR)2, R = oleyl, tetradecyl, M = Cd, Pb) are readily displaced from carboxylate-terminated ME nanocrystals (ME = CdSe, CdS, PbSe, PbS) by various Lewis bases (L = tri-n-butylamine, tetrahydrofuran, tetradecanol, N,N-dimethyl-n-butylamine, tri-n-butylphosphine, N,N,N',N'-tetramethylbutylene-1,4-diamine, pyridine, N,N,N',N'-tetramethylethylene-1,2-diamine, n-octylamine). The relative displacement potency is measured by 1H NMR spectroscopy and depends most strongly on geometric factors like sterics and chelation, though also on the hard/soft match with the cadmium ion. The results suggest that ligands displace L–M(O2CR)2 by cooperatively complexing the displaced metal ion as well as the nanocrystal. Removal of up to 90% of surface bound Cd(O2CR)2 from CdSe and CdS nanocrystals decreases the Cd:Se ratio from 1.1 ± 0.06 to 1.0 ± 0.05, broadens the 1Se-2S3/2h absorption and decreases the photoluminescence quantum yield (PLQY) from 10% to <1% (CdSe) and 20% to <1% (CdS). These changes are partially reversed upon rebinding of M(O2CR)2 at room temperature (~60 %) and fully reversed at elevated temperature. A model is proposed where electron accepting M(O2CR)2 complexes (Z-type ligands) reversibly bind to nanocrystals leading to a range of stoichiometries for a given core size. The results demonstrate that nanocrystals lack a single chemical formula, but are instead dynamic structures with concentration-dependent compositions. The importance of these findings to the synthesis and purification of nanocrystals as well as ligand exchange reactions is discussed.

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Section: Introductionmentioning

confidence: 99%

Ligand Exchange and the Stoichiometry of Metal Chalcogenide Nanocrystals: Spectroscopic Observation of Facile Metal-Carboxylate Displacement and Binding

et al. 2013

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“…29 Theoretical and computational modeling could provide a valuable insight into these issues. However, the lack of periodicity and the relatively large number of atoms make theoretical studies of QDs rather challenging.…”

Section: Introductionmentioning

confidence: 99%

Electronic Structure of Ligated CdSe Clusters: Dependence on DFT Methodology

et al. 2011

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Simulations of ligated semiconductor quantum dots (QDs) and their physical properties, such as morphologies, QDÀligand interactions, electronic structures, and optical transitions, are expected to be very sensitive to computational methodology. We utilize Density Functional Theory (DFT) and systematically study how the choice of density functional, atom-localized basis set, and a solvent affects the physical properties of the Cd 33 Se 33 cluster ligated with a trimethylphosphine oxide ligand. We have found that qualitative performance of all exchange-correlation (XC) functionals is relatively similar in predicting strong QDÀligand binding energy (∼1 eV). Additionally, all functionals predict shorter CdÀSe bond lengths on the QD surface than in its core, revealing the nature and degree of QD surface reconstruction. For proper modeling of geometries and QDÀligand interactions, however, augmentation of even a moderately sized basis set with polarization functions (e.g., LANL2DZ* and 6-31G*) is very important. A polar solvent has very significant implications for the ligand binding energy, decreasing it to 0.2À0.5 eV. However, the solvent model has a minor effect on the optoelectronic properties, resulting in persistent blue shifts up to ∼0.3 eV of the low-energy optical transitions. For obtaining reasonable energy gaps and optical transition energies, hybrid XC functionals augmented by a long-range HartreeÀFock orbital exchange have to be applied.

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“…The model clusters, used to reproduce the real nanocrystals, have been designed taking into account experimental information on the structure 8,9 , the reaction mechanism of formation 10,11 and surface passivation [12][13][14][15] of semiconductor nanocrystals. The present work has been focused of the (CdSe) 33 cluster which is the smallest CdSe nanocrystal isolated and characterized by mass spectrometry 16,17 .…”

Section: Introductionmentioning

confidence: 99%

Density Functional Study on the Morphology and Photoabsorption of CdSe Nanoclusters

et al. 2011

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The geometrical and electronic structures of a series of small CdSe quantum dots protected by various ligands have been studied by density functional theory. UV-vis spectra have been calculated by time-dependent density functional theory (TDDFT). The goal of this investigation is the rationalization of the basic properties of these systems, in particular, the nature of the exciton peaks. This study has been focused on the (CdSe)(x), x = 13, 19, 33, and 66, "magic-size" clusters that are characterized by high stability and large optical gaps. The geometries of the cluster are relaxed both in vacuum and in the presence of the surfactant ligands. To describe the interaction between the bare clusters and the surfactants, model types of ligands are introduced: fatty acids are modeled using formic and acetic acid and amines are modeled using ammonia and methyl amine. Present calculations demonstrate that the ligands play a crucial role in stabilizing the structure in a bulklike geometry and strongly affect the optical gap of the clusters, due to an optimal coordination of the surface atoms. For these "magic-size" clusters, the UV-vis spectrum is calculated at the TDDFT level. The calculated spectra are in good agreement with the experimental ones for clusters with the same dimension capped with the same type of Uganda. This suggests that our structures are realistic models of the actual quantum dots. 2

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Ligand exchange of CdSe nanocrystals probed by optical spectroscopy in the visible and mid-IR

Cited by 71 publications

References 36 publications

Ligand Exchange and the Stoichiometry of Metal Chalcogenide Nanocrystals: Spectroscopic Observation of Facile Metal-Carboxylate Displacement and Binding

Ligand Exchange and the Stoichiometry of Metal Chalcogenide Nanocrystals: Spectroscopic Observation of Facile Metal-Carboxylate Displacement and Binding

Electronic Structure of Ligated CdSe Clusters: Dependence on DFT Methodology

Density Functional Study on the Morphology and Photoabsorption of CdSe Nanoclusters

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