One-Step Route to Luminescent Au₁₈SG₁₄ in the Condensed Phase and Its Closed Shell Molecular Ions in the Gas Phase

We report a one-step route for the synthesis of highly luminescent and water-soluble Au₁₈SG₁₄ (SG- glutathione in thiolate form) in nearly pure form using a slow reduction process. The cluster shows step-like behavior in its absorption profile. It emits red light in both aqueous and solid state under UV illumination. Quantum yield of the cluster is 0.053, nearly 25-fold higher than that of Au₂₅SG₁₈. The cluster exhibits distinct features corresponding to multiply charged ions in electrospray ionization mass spectrometry. This composition is also confirmed from MALDI MS along with other quantitative analyses. The cluster makes closed shell molecular ions in the gas phase. The possibility of making clusters of different core sizes is also demonstrated. The simplicity of this method and identification of the cluster with exact composition may facilitate the exploration of experimental and theoretical research on this material

Low-Temperature Thermal Dissociation of Ag Quantum Clusters in Solution and Formation of Monodisperse Ag₂S Nanoparticles

We report the effect of temperature on the stability of glutathione-protected Ag₂₅ clusters. The clusters are stable up to 50 °C. Interestingly, above this temperature, they decompose to yield Ag₂S nanoparticles with an average diameter of 3 ± 1 nm, crystallizing in monoclinic acanthite polymorph. Unlike conventional methods of syntheses of Ag₂S, where a temperature of ∼200 °C is needed, our study shows the possibility of synthesis of Ag₂S nanoparticles at much lower temperatures. This is in contrast with silver nanoparticles protected with thiolates, which typically give silver and alkyl/aryl disulfide upon thermal activation. The mechanism of cluster decomposition and formation of silver sulphide nanoparticles was investigated using various analytical techniques such as ultraviolet–visible spectroscopy, X-ray diffraction scanning electron microscopy, energy-dispersive analysis of X-rays, transmission electron microscopy, and electrospray ionization mass spectrometry. The monolayer of the cluster undergoes S–C bond cleavage, as revealed by mass spectrometry. This is somewhat unusual because Ag–S cleavage is expected in view of its lower bond energy

Nucleation, Growth, and Structural Transformations of Perovskite Nanocrystals

Despite the recent surge of interest in lead halide perovskite nanocrystals, there are still significant gaps in the understanding of nucleation and growth processes involved in their formation. Using CsPbX₃ as a model system, we systematically study the formation mechanism of cubic CsPbX₃ nanocrystals, their growth via oriented attachment into larger nanostructures, and the associated phase transformations. We found evidence to support that the formation of CsPbX₃ NCs occurs through the seed-mediated nucleation method, where Pb° NPs formed during the course of reaction act as seeds. Further growth occurs through self-assembly and oriented attachment. The polar environment is a major factor in determining the structure and shape of the resulting nanoparticles, as confirmed by experiments with aged seed reaction mixtures, and by addition of polar additives. These results provide a fundamental understanding of the influence of the environment polarity on self-assembly, self-healing, and the ability to control the morphology and structure over the perovskite structures. As a result of this understanding, we were able to extend the synthesis to produce other materials such as CsPbBr₃ nanowires and orthorhombic CsPbI₃ nanowires with tunable length ranging from 200 nm to several microns

Dynamic Postpolymerization Modification Based on Knoevenagel Adducts of Meldrum’s Acid

Postpolymerization modification using “click” reactions has been proven to be a powerful method to build functional polymers, but the way to construct dynamic functional polymers remains challenging. In this work, CC/CN dynamic exchange reaction between Meldrum’s acid condensate and aldimine was employed to establish an efficient dynamic PPM method. Under the condition of catalyst free and room temperature, the conversion of PPM based on CC/CN dynamic exchange reaction can be up to more than 90%. Furthermore, reactive polymer coatings for in situ generating dyes with different absorbance wavelengths (λmax = 360–605 nm) and rewritable fluorescent papers were successfully developed by using dynamic PPM to tune the electron donor−π-acceptor structures in MA condensates on polymers

Dynamic Postpolymerization Modification Based on Knoevenagel Adducts of Meldrum’s Acid

Postpolymerization modification using “click” reactions has been proven to be a powerful method to build functional polymers, but the way to construct dynamic functional polymers remains challenging. In this work, CC/CN dynamic exchange reaction between Meldrum’s acid condensate and aldimine was employed to establish an efficient dynamic PPM method. Under the condition of catalyst free and room temperature, the conversion of PPM based on CC/CN dynamic exchange reaction can be up to more than 90%. Furthermore, reactive polymer coatings for in situ generating dyes with different absorbance wavelengths (λmax = 360–605 nm) and rewritable fluorescent papers were successfully developed by using dynamic PPM to tune the electron donor−π-acceptor structures in MA condensates on polymers