Insights into thiocyanate-enhanced photoluminescence in CsPbBr3 nanocrystals by ultrafast two-dimensional infrared spectroscopy.

Functionalization of perovskite nanocrystal surfaces with thiocyanate anions presents a transformative approach to enhancing stability and photoluminescence quantum yield (PLQY) through surface defect passivation. This study investigates the role of thiocyanate ligands in modifying the optoelectronic properties of CsPbBr3 nanocrystals. We employed ultrafast two-dimensional infrared spectroscopy to investigate the nature of the dynamic interaction of thiocyanate ligands with nanocrystal surfaces, providing insights into the mechanisms underlying the observed increase in PLQY and stability. Our analysis reveals that the thiocyanate ligands efficiently passivate the surface defects, thereby enhancing the PLQY and the stability of the treated nanocrystals. The spectroscopic evidence supports a model where thiocyanate binds to under-coordinated lead atoms, contributing to a stable nanocrystal surface with enhanced optoelectronic performance. This ligand-induced passivation mechanism advances our understanding of surface chemistry's role in optimizing nanomaterials for solar cell and LED applications.

Noble Metal Nanoparticles with Nanogel Coatings: Coinage Metal Thiolate-Stabilized Glutathione Hydrogel Shells.

Developing biocompatible nanocoatings is crucial for biomedical applications. Noble metal colloidal nanoparticles with biomolecular shells are thought to combine diverse chemical and optothermal functionalities with biocompatibility. Herein, we present nanoparticles with peptide hydrogel shells that feature an unusual combination of properties: the metal core possesses localized plasmon resonance, whereas a few-nanometer-thick shells open opportunities to employ their soft framework for loading and scaffolding. We demonstrate this concept with gold and silver nanoparticles capped by glutathione peptides stacked into parallel ß-sheets as they aggregate on the surface. A key role in the formation of the ordered structure is played by coinage metal(I) thiolates, i.e., Ag(I), Cu(I), and Au(I). The shell thickness can be controlled via the concentration of either metal ions or peptides. Theoretical modeling of the shell's molecular structure suggests that the thiolates have a similar conformation for all the metals and that the parallel ß-sheet-like structure is a kinetic product of the peptide aggregation. Using third-order nonlinear two-dimensional infrared spectroscopy, we revealed that the ordered secondary structure is similar to the bulk hydrogels of the coinage metal thiolates of glutathione, which also consist of aggregated stacked parallel ß-sheets. We expect that nanoparticles with hydrogel shells will be useful additions to the nanomaterial toolbox. The present method of nanogel coating can be applied to arbitrary surfaces where the initial deposition of the seed glutathione monolayer is possible.

Oyster Pearl-Shaped Ternary Iron Chalcogenide, FeSe0.5Te0.5, Films on FTO through Electrochemical Growth from the Exchange of Chalcogens Boosted the Enzyme-Free Urea-Sensing Ability toward Real Analytes.

Here, iron chalcogenide thin films were developed for the first time by using the less hazardous electrodeposition technique at optimized conditions on an FTO glass substrate. The chalcogenides have different surface, morphological, structural, and optical properties, as well as an enzyme-free sensing behavior toward urea. Numerous small crystallites of about ∼20 to 25 nm for FeSe, ∼18 to 25 nm for FeTe, and ∼18 to 22 nm in diameter for FeSeTe are observed with partial agglomeration under an electron microscope, having a mixed phase of tetragonal and orthorhombic structures of FeSe, FeTe, and, FeSeTe, respectively. Profilometry, XRD, FE-SEM, HR-TEM, XPS, EDX, UV-vis spectroscopy, and FT-IR spectroscopy were used for the analysis of binary and ternary composite semiconductors, FeSe, FeTe, and FeSeTe, respectively. Electrochemical experiments were conducted with the chalcogenide thin films and urea as the analyte in phosphate-buffered media at a pH of ∼ 7.4 in the concentration range of 3-413 µM. Cyclic voltammetry was performed to determine the sensitivity of the prepared electrode at an optimized scan rate of 50 mV s-1. The electrodeposited chalcogenide films appeared with a low detection limit and satisfactory sensitivity, of which the ternary chalcogenide film has the lowest LOD of 1.16 µM and the maximum sensitivity of 74.22 µA µM-1 cm-2. The transition metal electrode has a very wide range of detection limit of 1.25-2400 µM with a short response time of 4 s. This fabricated biosensor is capable of exhibiting almost 75% of its starting activity after 2 weeks of storage in the freezer at 4 °C. Simple methods of preparation, a cost-effective process, and adequate electrochemical sensing of urea confirm that the prepared sensor is suitable as an enzyme-free urea sensor and can be utilized for future studies.

Vibrational Polaritons in Disordered Molecular Ensembles.

Disorder is an intrinsic attribute of any realistic molecular system. It is known to lead to localization, which hampers efficient transport. It was recently proposed that in molecular ensembles strongly coupled to photonic cavities, moderate disorder leads to delocalization and increases of the transport and chemical reaction rates. Vibrational polaritons involve molecular vibrations hybridized with an infrared cavity. When the coupling strength largely exceeds the molecular inhomogeneity, polaritons are unaffected by disorder. However, in many experiments, such a homogeneous limit does not apply. We investigated vibrational polaritons involving molecular ensembles with systematically modified disorder. Counterintuitively, moderate disorder leads to an increase in Rabi splitting and the modification of the polariton bandwidths. Experimental spectroscopic data agree with a Tavis-Cummings-like model that suggests enhanced delocalization of the reservoir states occurs via the admixture of the cavity mode. Our results provide new insights into the paradigm of disorder-induced cavity-assisted delocalization in molecular polaritons.

Infrared Open Cavities for Strong Vibrational Coupling.

Arrays of subwavelength plasmonic nanoparticles exhibiting narrowband lattice resonances are referred to as open cavities because of their ability to strongly couple with electronic excitations in molecular chromophores. However, realization of these ideas in the mid-infrared spectral region has been limited. We demonstrated a dramatic reduction in the bandwidth of lattice resonances in large-area arrays of half-wavelength mid-infrared antennas, reaching resonance quality factors above 200. By tuning the wavelength of the antenna-lattice resonances (ALR) to match the transition frequency of the molecular vibrational modes, we achieved a strong coupling between the ALR and the carbonyl stretching excitation in a thin film of (poly)methyl methacrylate (PMMA) polymer deposited on the array. Splitting of the polaritonic transitions, reduction of their bandwidth below that of the bare molecular transition, and characteristic dispersion confirmed the strong coupling regime. Our results pave the way for exciting research on the many-body correlated dynamics of vibrational polaritons.

Glutathione Self-Assembles into a Shell of Hydrogen-Bonded Intermolecular Aggregates on "Naked" Silver Nanoparticles.

A detailed understanding of the molecular structure in nanoparticle ligand capping layers is crucial for their efficient incorporation into modern scientific and technological applications. Peptide ligands render the nanoparticles as biocompatible materials. Glutathione, a γ-ECG tripeptide, self-assembles into aggregates on the surface of ligand-free silver nanoparticles through intermolecular hydrogen bonding and forms a few nanometer-thick shells. Two-dimensional nonlinear infrared (2DIR) spectroscopy suggests that aggregates adopt a conformation resembling the ß-sheet secondary structure. The shell thickness was evaluated with localized surface plasmon resonance spectroscopy and X-ray photoelectron spectroscopy. The amount of glutathione on the surface was obtained with spectrophotometry of a thiol-reactive probe. Our results suggest that the shell consists of ∼15 stacked molecular layers. These values correspond to the inter-sheet distances, which are significantly shorter than those in amyloid fibrils with relatively bulky side chains, but are comparable to glycine-rich silk fibrils, where the side chains are compact. The tight packing of the glutathione layers can be facilitated by hydrogen-bonded carboxylic acid dimers of glycine and the intermolecular salt bridges between the zwitterionic γ-glutamyl groups. The structure of the glutathione aggregates was studied by 2DIR spectroscopy of the amide-I vibrational modes using 13C isotope labeling of the cysteine carbonyl. Isotope dilution experiments revealed the coupling of modes forming vibrational excitons along the cysteine chain. The coupling along the γ-glutamyl exciton chain was estimated from these values. The obtained coupling strengths are slightly lower than those of native ß-sheets, yet they appear large enough to point onto an ordered conformation of the peptides within the aggregate. Analysis of the excitons' anharmonicities and the strength of the transition dipole moments generally is in agreement with these observations.

Polymer-assisted drug sequestration from plasma protein by a surfactant with curtailed denaturing capacity.

The capability of a surfactant to sequester a drug bound to plasma protein was investigated using steady-state and time-resolved spectroscopic techniques. Surfactants are known to denature protein, and hence are not suitable for the sequestration of a drug from protein. Herein, we show that the denaturing capacity of a surfactant is curtailed completely and its drug sequestration power is enhanced in the presence of biocompatible Pluronic micelles due to the formation of unique supramolecular assemblies. Further, our detailed studies indicate that the concentration of surfactant required for the sequestration of a drug is less than its critical micellar concentration (CMC). The extent of sequestration of drug by polymer-surfactant supramolecular assemblies can be tuned finely by controlling the concentration of surfactant. Detailed analysis showed that up to ∼85% sequestration of a drug from plasma protein could be achieved using a sub-CMC concentration of surfactant. Our results clearly show that controlled sequestration of a drug from plasma protein can be achieved with a reduction in the protein denaturing properties of surfactants.