RESUMEN
Silver cluster-based solids have garnered considerable attention owing to their tunable luminescence behavior. While surface modification has enabled the construction of stable silver clusters, controlling interactions among clusters at the molecular level has been challenging due to their tendency to aggregate. Judicious choice of stabilizing ligands becomes pivotal in crafting a desired assembly. However, detailed photophysical behavior as a function of their cluster packing remained unexplored. Here, we modulate the packing pattern of Ag12 clusters by varying the nitrogen-based ligand. CAM-1 formed through coordination of the tritopic linker molecule and NC-1 with monodentate pyridine ligand; established via non-covalent interactions. Both the assemblies show ligand-to-metal-metal charge transfer (LMMCT) based cluster-centered emission band(s). Temperature-dependent photoluminescence spectra exhibit blue shifts at higher temperatures, which is attributed to the extent of the thermal reverse population of the S1 state from the closely spaced T1 state. The difference in the energy gap (ΔEST ) dictated by their assemblies played a pivotal role in the way that Ag12 cluster assembly in CAM-1 manifests a wider ΔEST and thus requires higher temperatures for reverse intersystem crossing (RISC) than assembly of NC-1. Such assembly-defined photoluminescence properties underscore the potential toolkit to design new cluster- assemblies with tailored optoelectronic properties.
RESUMEN
Atom-precise metal nanoclusters, which contain a few tens to hundreds of atoms, have drawn significant interest due to their interesting physicochemical properties. Structural analysis reveals a fundamental architecture characterized by a central core or kernel linked to a staple motif with metal-ligand bonding playing a pivotal role. Ligands not only protect the surface but also exert a significant influence in determining the overall assembly of the larger superstructures. The assemblies of nanoclusters are driven by weak interaction between the ligand molecules; it also depends on the ligand type and functional group present. Here, we report an achiral ligand and Ag(I)···Ag(I) interaction-driven spontaneous resolution of silver-thiolate structure, [Ag18(C6H11S)12(CF3COO)6(DMA)2], where silver atoms and cyclohexanethiolate are connected to form a one-dimensional chain with helicity. Notably, silver atoms adopt different types of coordination modes and geometries. The photoluminescence properties of the one-dimensional (1D) chain structure were investigated, and it was found to exhibit excitation-dependent emission properties attributed to hydrogen-bonding interactions. Experimental and theoretical investigations corroborate the presence of triplet-emitting ligand-to-metal charge-transfer transitions.
RESUMEN
Anion-templated silver nanoclusters are fascinating to study because of their diverse structures, which are dictated by the nature of both anions and ligands. Here, we used the bulky 1-ethynyladamantane as one of the protecting ligands alongside trifluoracetate to successfully synthesize a chlorine-templated silver nanoclusterâCl@Ag19(C12H15)11(C2O2F3)7. Elucidation of its structure by single crystal X-ray diffraction revealed the structure to be a chlorine-centered Ag19 cage with protection by alkynyl and carboxylic ligands. This cluster is non-emissive at room temperature and showed green emission with a large Stokes shift at low temperature. The crystal structure was found to be quasi-isomeric with a previously reported Ag19 cluster protected by tert-butyl acetylene, which is emissive at room temperature. Detailed photoluminescence studies and structure-property correlation revealed that the arrangement of the silver skeleton which is influenced by the bulky substituent of the ligand might be responsible for the difference in emission properties.
RESUMEN
Astrocytes are essential to brain homeostasis and their dysfunction can have devastating consequences on human quality of life. Such deleterious effects are generally due in part to changes that occur at the cellular level, which may be biochemical or biomechanical in nature. One biomechanical change that can occur is a change in tissue stiffness. Brain tumors are generally associated with increased brain tissue stiffness, but the impact increased tissue stiffness has on astrocyte biomechanical behavior is poorly understood. Therefore, in this study we cultured human astrocytes on flexible substrates with stiffness that mimicked the healthy human brain (1 kPa), meningioma (4 kPa), and glioma (11 kPa) and investigated astrocyte biomechanical behavior by measuring cell-substrate tractions, strain energies, cell-cell intercellular stresses, and cellular velocities. In general, tractions, intercellular stresses, and strain energy was observed to increase as a function of increased substrate stiffness, while cell velocities were observed to decrease with increased substrate stiffness. We believe this study will be of great importance to the fields of brain pathology and brain physiology.
