Seed-mediated synthesis strategies, in which small gold nanoparticle precursors are added to a growth solution to initiate heterogeneous nucleation, are among the most prevalent, simple, and productive methodologies for generating well-defined colloidal anisotropic nanostructures. However, the size, structure, and chemical properties of the seeds remain poorly understood, which partially explains the lack of mechanistic understanding of many particle growth reactions. Here, we identify the majority component in the seed solution as an atomically precise gold nanocluster, consisting of a 32-atom Au core with 8 halide ligands and 12 neutral ligands constituting a bound ion pair between a halide and the cationic surfactant: Au32X8[AQA+•X-]12(X = Cl, Br; AQA = alkyl quaternary ammonium). Ligand exchange is dynamic and versatile, occurring on the order of minutes and allowing for the formation of 48 distinct Au32clusters with AQAX (alkyl quaternary ammonium halide) ligands. Anisotropic nanoparticle syntheses seeded with solutions enriched in Au32X8[AQA+•X-]12show narrower size distributions and fewer impurity particle shapes, indicating the importance of this cluster as a precursor to the growth of well-defined nanostructures.
Instability of colloidal iodine‐based inorganic perovskite CsPbX3(X = Cl, Br, I) nanocrystals (IPNCs) represents a major obstacle in lead‐halide IPNC research and application. Herein, a ligand‐anchoring process is reported that enables significantly improved colloidal stability of the iodine‐based IPNCs for over 10 months in ambient. Apart from the previous efforts in searching for strong binding ligands to cap the IPNCs to incrementally reduce the exposure of the IPNC surface to the harsh colloidal environment, the ligand‐anchoring method demonstrates that such an exposure can be reduced substantially by suppressing the dynamic ligand exchange around the colloidal IPNCs. In the IPNC synthesis solution with common oleic acid (OA) and oleylamine (OLA) ligands with relative weak binding to IPNCs, a systematic reduction of the ligand concentration using hexane by an order of magnitude has shown to be effective in achieving OA/OLA ligand‐anchored iodine‐based IPNCs with superior stability as confirmed in optical absorption, photoluminescence,1H solution nuclear magnetic resonance spectroscopy, and photoresponse. This result has revealed that the intermittent exposure of the IPNC surface during the dynamic ligand exchange is a primary mechanism underlying the colloidal IPNC instability, which can be resolved in the ligand‐anchoring process by suppressing such dynamic activities.
more » « less- NSF-PAR ID:
- 10362086
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 9
- Issue:
- 22
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
As surface ligands play a critical role in the colloidal stability and optoelectronic properties of semiconductor nanocrystals, we used solution NMR experiments to investigate the surface coordination chemistry of Ge nanocrystals synthesized by a microwave-assisted reduction of GeI 2 in oleylamine. The as-synthesized Ge nanocrystals are coordinated to a fraction of strongly bound oleylamide ligands (with covalent X-type Ge–NHR bonds) and a fraction of more weakly bound (or physisorbed) oleylamine, which readily exchanges with free oleylamine in solution. The fraction of strongly bound oleylamide ligands increases with increasing synthesis temperature, which also correlates with better colloidal stability. Thiol and carboxylic acid ligands bind to the Ge nanocrystal surface only upon heating, suggesting a high kinetic barrier to surface binding. These incoming ligands do not displace native oleylamide ligands but instead appear to coordinate to open surface sites, confirming that the as-prepared nanocrystals are not fully passivated. These findings will allow for a better understanding of the surface chemistry of main group nanocrystals and the conditions necessary for ligand exchange to ultimately maximize their functionality.more » « less
-
Enhancing Photostability of Sn‐Pb Perovskite Solar Cells by an Alkylammonium Pseudo‐Halogen Additivemore » « less
Abstract High‐performance tin‐lead perovskite solar cells (PSCs) are needed for all‐perovskite‐tandem solar cells. However, iodide related fast photodegradation severely limits the operational stability of Sn‐Pb perovskites despite the demonstrated high efficiency and thermal stability. Herein, this work employs an alkylammonium pseudo‐halogen additive to enhance the power conversion efficiency (PCE) and photostability of methylammonium (MA)‐free, Sn‐Pb PSCs. Density functional theory (DFT) calculations reveal that the pseudo‐halogen tetrafluoroborate (BF4−) has strong binding capacity with metal ions (Sn2+/Pb2+) in the Sn‐Pb perovskite lattice, which lowers iodine vacancy formation. Upon combining BF4−with an octylammonium (OA+) cation, the PCE of the device with a built‐in light‐scattering layer is boosted to 23.7%, which represents a new record for Sn‐Pb PSCs. The improved efficiency benefits from the suppressed defect density. Under continuous 1 sun illumination, the OABF4embodied PSCs show slower generation of interstitial iodides and iodine, which greatly improves the device photostability under open‐circuit condition. Moreover, the device based on OABF4retains 88% of the initial PCE for 1000 h under the maximum‐power‐point tracking (MPPT) without cooling.
-
Osiński, Marek ; Kanaras, Antonios G. (Ed.)N-heterocyclic carbenes (NHCs) have attracted tremendous attention over the past decade, as it is expected to form strong coordination to transition metal complexes and surfaces. Here, we investigate the interactions between colloidal gold nanoparticles (AuNPs), or luminescent quantum dots (QDs) and a multidentate NHC-based polymer ligand. The ligand design relies on the nucleophilic addition reaction between several NHC anchoring groups, short polyethylene glycol (PEG) blocks, and a polymer chain. We find that such NHC-decorated ligands rapidly coordinate onto both sets of nanocrystals, which is attributed to the inherent σ-donating nature (soft Lewis base) of NHC groups combined with the soft Lewis acidic character of nanocrystal surfaces. We combine NMR spectroscopy, fluorescence spectroscopy, high-resolution transmission electron microscopy and dynamic light scattering to characterize the NHCstabilized nanocrystals and gain insights into the nature of the binding interactions. In particular, we find that the newly coated nanocrystals exhibit long-term colloidal stability over a broad range of conditions with no sign of degradation or aggregation build up, while preserving their photophysical properties, for at least one year of storage.more » « less
-
more » « less
Abstract In this study, the binding of multimodal chromatographic ligands to the IgG1 FCdomain were studied using nuclear magnetic resonance and molecular dynamics simulations. Nuclear magnetic resonance experiments carried out with chromatographic ligands and a perdeuterated15N‐labeled FCdomain indicated that while single‐mode ion exchange ligands interacted very weakly throughout the FCsurface, multimodal ligands containing negatively charged and aromatic moieties interacted with specific clusters of residues with relatively high affinity, forming distinct binding regions on the FC. The multimodal ligand‐binding sites on the FCwere concentrated in the hinge region and near the interface of the CH2 and CH3 domains. Furthermore, the multimodal binding sites were primarily composed of positively charged, polar, and aliphatic residues in these regions, with histidine residues exhibiting some of the strongest binding affinities with the multimodal ligand. Interestingly, comparison of protein surface property data with ligand interaction sites indicated that the patch analysis on FCcorroborated molecular‐level binding information obtained from the nuclear magnetic resonance experiments. Finally, molecular dynamics simulation results were shown to be qualitatively consistent with the nuclear magnetic resonance results and to provide further insights into the binding mechanisms. An important contribution to multimodal ligand‐FCbinding in these preferred regions was shown to be electrostatic interactions and π–π stacking of surface‐exposed histidines with the ligands. This combined biophysical and simulation approach has provided a deeper molecular‐level understanding of multimodal ligand–FCinteractions and sets the stage for future analyses of even more complex biotherapeutics.
