The successful growth of colloidal lead halide perovskite quantum dots (PQDs) has generated tremendous interest in the community, due to the unique properties and the promise PQDs offer for use in applications involving light-emitting devices and solar cell technology. However, tangible progress in probing their fundamental properties and/or their integration into optoelectronic devices has been hampered by issues of colloidal and photophysical instability. Here, we introduce a promising surface coating strategy relying on a polyzwitterion polymer, where high-affinity binding onto the QDs is driven by multicoordinating electrostatic interactions with the ion-rich surfaces of CsPbBr3 PQDs. The polymer ligands were synthesized by installing a stoichiometric mixture of amine-modified sulfobetaine anchors and solubilizing motifs on poly­(isobutylene-alt-maleic anhydride), PIMA, via nucleophilic addition reaction. We find that this coating approach imparts enhanced colloidal and photophysical stability to the nanocrystals over a broad range of solvent conditions and in powder form. This approach also allows easy phase transfer of the PQDs from nonpolar media to an array of solutions with varying polarities and properties. Additionally, the stabilization strategy preserves the photophysical and structural characteristics of the nanocrystals over a period extending to 1.5 years under certain conditions.

Coding metasurfaces, composed of an array of coding particles with discrete phase responses, are encoded with predesigned coding sequences to manipulate wavefronts of electromagnetic (EM) waves and realize novel functionalities such as anomalous beam deflection, broadband diffusion, and polarization conversion. Such a new concept can be viewed as a bridge linking metamaterial and digital codes, yielding the investigation of metamaterials from a digital perspective and eventually the realization of real-time control of EM waves. Here, we propose and experimentally demonstrate a transmission-type coding metasurface to bend normally incident terahertz beams in anomalous directions and generate nondiffractive Bessel beams in normal and oblique directions. To overcome the larger reflection and strong Fabry−Perot resonance that usually originate from a thick silicon substrate, a free-standing design is presented for the coding particle, which is formed by stacking three metallic layers with four polyimide spacers alternately. Experimental results show that the fabricated sample could bend the normally incident terahertz wave to anomalous refraction angles of 26°and 58°with 58% and 40% efficiencies, respectively. Owing to the excellent mechanical and chemical properties of polyimide, the fabricated sample is extremely flexible and stable, implying promising applications in terahertz imaging and communication.

We describe the effectiveness of a multicoordinating polymer coating to surface functionalize gold nanospheres, nanoshells, and nanorods and promote their steric stabilization in biological media. The polymer ligand synthesized via one-step nucleophilic addition reaction starting with poly­(isobutylene-alt-maleic anhydride) precursor presents multiple lipoic acid groups for strong coordination on metal-rich surfaces and several hydrophilic motifs (e.g., zwitterion groups or short poly­(ethylene glycol) (PEG) chains) to promote water solubilization. We show that nanocrystals ligated with this polymer are compact in size and exhibit excellent long-term colloidal stability over broad conditions. We compare the ability of zwitterion- and PEG-modified polymer ligands to shield the metal surfaces from sodium cyanide digestion, or resist the competitive removal by dithiothreitol (DTT). We find that polymers appended with either hydrophilic motif essentially eliminate DTT competition for surface binding, while nanocrystals capped with the PEGylated coating exhibits substantially better resistance to sodium cyanide digestion compared with zwitterionic coating. Furthermore, we probe the differences between the two coatings in terms of endowing surface charge to the nanocrystals and affecting their Brownian diffusion properties. Additionally, we show that zwitterionic coating is very effective in preventing the formation of protein corona on such nanostructures, a highly valuable result with direct implications in biotechnology.

Reacting poly­(maleic anhydride)-based polymers with H2N–R nucleophiles is a flexible and highly effective approach for preparing a variety of multifunctional, multicoordinating, and multireactive polymers. The exact transformation of the anhydride ring during this addition reaction is still an open question. In this report, we characterize the transformation of a representative block copolymer, poly­(isobutylene-alt-maleic anhydride), with a few H2N–R nucleophiles. In particular, we test the effects of varying a few reaction parameters/conditions (e.g., temperature, solvent, reaction time, and addition of thionyl chloride) on the nature of the anhydride transformation and bond formed between the polymer and the lateral R groups. The resulting polymers are characterized using a combination of analytical techniques including FT-IR, one- and two-dimensional NMR, and gel electrophoresis. We find that the ring opening transformation occurs under mild conditions. Conversely, cyclic imide transformation can take place for reactions carried out at high temperature (e.g., in DMF under refluxing conditions). We also find that use of a protic solvent, such as methanol, or addition of thionyl chloride (SOCl2) to the reaction mixture under refluxing conditions can promote cyclic imide transformation. The cyclic imide transformation is nonetheless partial, as carboxyl groups could still be accounted for in the resulting compounds. Depending on the type of transformation, the resulting polymer can exhibit a few distinct properties, such as net charge buildup along the chain, or the appearance of weak UV–vis absorption and fluorescence properties. These findings are useful for understanding the properties exhibited by polymer materials prepared via this flexible and highly effective route using anhydride containing polymers and oligomers.

An effective and easy to implement ligand exchange strategy is paramount to the design of stable and multifunctional gold and other inorganic nanocolloids. This is also crucial for their use in biology and medicine. In this contribution, we demonstrate that photomediated ligand substitution of gold nanocrystals with a series of lipoic acid-modified ligands yields several advantages, including rapid phase transfer and great long-term colloidal stability. This strategy combines photochemical reduction of the dithiolane group with energetically favorable in situ ligand chemisorption, yielding rapid modification of the surfaces. It requires substantially smaller amounts of excess ligands compared to conventional incubation starting with the oxidized form of the ligands. Complete substitution of the ligands is confirmed by using 1 H NMR and FT-IR spectroscopy. The colloidal properties of the resulting materials have been tested by using a combination of longterm stability in ion-rich media, sodium cyanide digestion, and dithiothreitol competition tests. They show that photoligation preserves the structure and photophysical properties of the various colloids. Mechanistic arguments have been discussed to explain the effectiveness of this ligation strategy. These findings prove the practical benefits of this approach for designing biocompatible gold colloids and bode well for using such materials in a variety of biological assays and photothermal therapy.

Over the past decade, N-heterocyclic carbenes (NHCs) have attracted remarkable attention as metal-coordinating ligands because of their ability to strongly interact with transition metal complexes and surfaces. We investigate the coordination interaction between colloidal gold nanoparticles (AuNPs) and three sets of hydrophilic NHC-based ligands: an amine-modified small molecule, a monomeric NHC appended with a poly­(ethylene glycol) (PEG) block, and a modified poly­(isobutylene-alt-maleic anhydride), PIMA, that simultaneously presents multiple NHC groups and several short PEG chains. In this report, we find that all three ligands can rapidly coordinate onto AuNPs, as characterized using a combination of NMR spectroscopy, high-resolution transmission electron microscopy, and dynamic light scattering. These measurements have been supplemented with colloidal stability tests as well as competition from dithiothreitol molecules. Overall, we find that multidentate NHC polymer coating exhibits the highest affinity to AuNPs, which manifests in long-term colloidal stability in buffer media, absence of any aggregation, and better resistance to competition from reducing molecules. We further exploit these data to infer additional insights into the interaction and coordination of NHC molecules with Au surfaces.

We detail the design of a new set of multicoordinating polymer ligands based on the phosphonate anchoring motif and apply them for the surface coating of luminescent quantum dots, gold nanoparticles, and iron oxide nanoparticles alike. The ligand is synthesized via a nucleophilic addition reaction between poly­(isobutylene-alt-maleic anhydride) and amine-modified phosphonate derivatives and short polyethylene glycol hydrophilic blocks, which allows the flexibility to tune the architecture and stoichiometry of the final compound. We find that these phosphonate-based polymers exhibit a strong coordinating affinity for ZnS-overcoated quantum dots (QDs), Au nanoparticles, and iron oxide nanoparticles, yielding nanocrystal dispersions that exhibit good colloidal stability for all three systems. The affinity of these ligands is also preserved when additional coordinating groups are introduced, such as imidazoles. Furthermore, the resulting polymer-coated nanocrystals are easily functionalized with reactive groups, introduced along the polymer chain during synthesis. The polymer coating is compact enough to allow implementation of resonance energy transfer coupling of luminescent QDs to proximal dyes. The affinity between the ligands and gold nanoparticle surfaces was compared to that of thiol groups using NaCN digestion tests.

We have tested the ability of N-heterocyclic carbene (NHC)-modified ligands to coordinate and stabilize luminescent CdSe−ZnS core−shell quantum dot (QD) dispersions in hydrophilic media. In particular, we probed the effects of ligand structure and coordination number on the coating affinity to the nanocrystals. We find that such NHC-based ligands rapidly coordinate onto the QDs (requiring ∼5−10 min of reaction time), which reflects the soft Lewis base nature of the NHC groups, with its two electrons sharing capacity. Removal of the hydrophobic cap and promotion of carbenedriven coordination on the nanocrystals have been verified by 1 H NMR spectroscopy, while 13 C NMR was used to identify the formation of carbene−Zn complexes. The newly coated QD dispersions exhibit great long-term colloidal stability over a wide range of conditions. Additionally, we find that coordination onto the QD surfaces affects the optical and spectroscopic properties of the nanocrystals. These include a size-dependent red-shift of the absorption and fluorescence spectra and a pronounced increase in the measured fluorescence intensity when the samples are stored under white light exposure compared to those stored in the dark.