Electrostatic-Driven Self-Assembly of Janus-like Monolayer-Protected Metal Nanoclusters

Solvent-Modulated Luminescent Spheroidal Assemblies of Cu8 Nanocluster for Volatile Amine Sensing

Cluster-assembled luminescent microstructures built with metal nanoclusters (NCs) represent a promising class of nanomaterials with diverse applications in photonics and sensing. In this work, we have designed a strategy to make a photoluminescent material by assembling atom-precise NCs of [Cu8(TFMPT)4(DPPE)4] (abbreviated as Cu8), where TFMPT is 4-hydroxy-6-(trifluoromethyl) pyrimidine-2-thiolate and DPPE is 1,2-bis(diphenylphosphino)ethane. Single-crystal X-ray diffraction (SC-XRD) reveals a unique tetracapped tetrahedral Cu8 core structure. Upon gradual addition of water (50-85 vol %) to the visibly nonluminescent dimethylformamide (DMF) solution of the clusters, a strong orange luminescence (emission at 625 nm under ultraviolet (UV) light) was observed. It is due to the formation of spheroidal assemblies of nanometer dimension. The cluster-assembled spheroids (CASs) are formed due to hydrophobic interactions among clusters as the concentration of water increases in the solution. Time-correlated single-photon counting reveals that the lifetime of luminescent aggregates is on a microsecond scale, which suggests phosphorescence. Such phosphorescent CASs show a fast response, high selectivity, and naked-eye detection of volatile amines (VAs). Spectroscopic studies and density functional theory (DFT) calculations provide an in-depth understanding of luminescence quenching of CASs and a mechanistic understanding of ammonia and trimethyl amine sensing. The limits of detection (LoD) of ammonia and trimethyl amine were measured to be 0.568 × 10-7 M (0.001 ppm) and 0.362 0.568 × 10-7 M (0.002 ppm), respectively. Overall, apart from enriching the family of copper clusters, this work additionally introduces a new photoluminescent material for volatile organic amine (VOA) compound sensing of environmental relevance.

Charge-Segregated Ion-Pairing Assemblies Comprising Dipolar π-Electronic Cations

Two pentamethine dyes with nearly identical structures but slightly different dipole moments were prepared as ion pairs. The ion pairs provided charge-segregated assemblies stabilized by dipole-dipole interactions between the positively charged π-electronic systems. The stacking structure of the bromo-substituted pentamethine cation was more stabilized by a larger dipole moment, as suggested by energy decomposition analysis. Depending on the packing arrangements, highly electric conductive properties were observed owing to charge-segregated structures, as also correlated with the theoretically estimated transfer integrals.

A molecular dynamics study on the ion-mediated self-assembly of monolayer-protected nanoclusters

We studied the effects of metal and molecular cations on the aggregation of atomically precise monolayer-protected nanoclusters (MPCs) in an explicit solvent using atomistic molecular dynamics simulations. While divalent cations such as Zn2+ and Cd2+ promote aggregation by forming ligand-cation-ligand bridges between the MPCs, molecular cations such as tetraethylammonium and cholinium inhibit their aggregation by getting adsorbed into the MPC's ligand shell and reducing the ligand's motion. Here, we studied the aggregation of Au25(SR)18 nanoclusters with two types of ligands, para-mercaptobenzoic acid and D-penicillamine, as prototypical examples.

The effect of ligands on the size distribution of copper nanoclusters: Insights from molecular dynamics simulations

Controlling the size distribution in the nucleation of copper particles is crucial for achieving nanocrystals with desired physical and chemical properties. However, their synthesis involves a complex system of solvents, ligands, and copper precursors with intertwining effects on the size of the nanoclusters. We combine molecular dynamics simulations and density functional theory calculations to provide insights into the nucleation mechanism in the presence of a triphenyl phosphite ligand. We identify the crucial role of the strength of the metal-phosphine interaction in inhibiting the cluster's growth. We demonstrate computationally several practical routes to fine-tune the interaction strength by modifying the side groups of the additive. Our work provides molecular insights into the complex nucleation process of protected copper nanocrystals, which can assist in controlling their size distribution and, eventually, their morphology.