Aggregation-induced phosphorescence sensitization in two heptanuclear and decanuclear gold-silver sandwich clusters

A Highly NIR Emissive Cu16 Pd1 Nanocluster

The construction of stable copper nanoclusters (Cu-NCs) with near-infrared (NIR) emission that can be used for catalysis is highly desired, yet remains a challenge. Herein, an atomically precise bimetallic Cu/Pd NC with a molecular formula of Cu16 Pd1 L10 (PPh3 )2 (Pz)6 (Pz = 3,5-(CF3 )2 Pyrazolate, L = 4-CH3 OPhC≡C- ), abbreviated as Cu16 Pd1 , is synthesized. Single-crystal X-ray crystallographic analysis of Cu16 Pd1 reveals a Cu10 Pd1 kernel with pseudo-gyroelongated square bipyramid confirmation surrounded by other 6 Cu(I) ions and protected ligands. Interestingly, it exhibits strong NIR emission with the highest photoluminescence quantum yield (PLQY) among all the Cu NCs/Cu alloys (λem  > 800 nm) in the solid-state, and also displays NIR emission in solution. Experimental results and theoretical calculations suggest that the impressive NIR emission is attributed to abundant supramolecular interactions in the solid-state, including intramolecular metal-metal and intermolecular interactions. Of note, the bimetallic Cu16 Pd1 can catalyze the reduction of 4-nitrophenol. This work provides a novel method for synthesizing Cu/Pd NCs and reminds that the less studied Cu/Pd NC can serve as outstanding luminescent material, which is seldom noticed in atomically precise nanoclusters.

Photoluminescence control by atomically precise surface metallization of C-centered hexagold(i) clusters using N-heterocyclic carbenes

The properties of metal clusters are highly dependent on their molecular surface structure. The aim of this study is to precisely metallize and rationally control the photoluminescence properties of a carbon(C)-centered hexagold(i) cluster (CAu^I₆) using N-heterocyclic carbene (NHC) ligands with one pyridyl, or one or two picolyl pendants and a specific number of silver(i) ions at the cluster surface. The results suggest that the photoluminescence of the clusters depends highly on both the rigidity and coverage of the surface structure. In other words, the loss of structural rigidity significantly reduces the quantum yield (QY). The QY in CH₂Cl₂ is 0.04 for [(C)(Au^I-BIPc)₆Ag^I₃(CH₃CN)₃](BF₄)₅ (BIPc = N-isopropyl-N'-2-picolylbenzimidazolylidene), a significant decrease from 0.86 for [(C)(Au^I-BIPy)₆Ag^I₂](BF₄)₄ (BIPy = N-isopropyl-N'-2-pyridylbenzimidazolylidene). This is due to the lower structural rigidity of the ligand BIPc because it contains a methylene linker. Increasing the number of capping Ag^I ions, i.e., the coverage of the surface structure, increases the phosphorescence efficiency. The QY for [(C)(Au^I-BIPc²)₆Ag^I₄(CH₃CN)₂](BF₄)₆ (BIPc² = N,N'-di(2-pyridyl)benzimidazolylidene) recovers to 0.40, 10-times that of the cluster with BIPc. Further theoretical calculations confirm the roles of Ag^I and NHC in the electronic structures. This study reveals the atomic-level surface structure-property relationships of heterometallic clusters.

Electrostatic Interaction-Induced Aggregation-Induced Emission-Type AgAu Bimetallic Nanoclusters as a Highly Efficient Electrochemiluminescence Emitter for Ultrasensitive Detection of Glial Fibrillary Acidic Protein

Herein, the aggregation-induced emission (AIE)-type carboxymethyl chitosan (CMCS)@6-aza-2-thiothymine (ATT) templated AgAu bimetallic nanoclusters (CMCS@ATT-AgAu BMNCs) with superior electrochemiluminescence (ECL) emission were first synthesized to construct a biosensor for the ultrasensitive detection of glial fibrillary acidic protein (GFAP). Impressively, unlike the traditional AIE-type bimetallic nanoclusters (BMNCs) obtained by complicated multi-step synthesis, the AIE-type CMCS@ATT-AgAu BMNCs were prepared by the electrostatic interaction between the negatively charged ATT and positively charged CMCS, in which the molecule ATT was served as a capping and reducing agent of bimetal ions. In addition, a rapidly moving cholesterol labeled DNA walker was constructed to move freely on the lipid bilayer to increase its moving efficiency, and the well-regulated DNA was intelligently designed to further improve its walking efficiency for rapid and ultrasensitive detection of GFAP with a limit of detection (LOD) as low as 73 ag/mL. This strategy proposed an avenue to synthesize highly efficient BMNCs-based ECL emitters, which have great potential in ultrasensitive biosensing for early diagnosis of diseases.

Relativistic modulation of supramolecular halogen/copper interactions and phosphorescence in Cu(I) pyrazolate cyclotrimers

Described herein are the synthesis, structure, and photophysics of the iodo-substituted cyclic trinuclear copper(I) complex, Cu₃[4-I-3,5-(CF₃)₂Pz]₃ supported by a highly-fluorinated pyrazolate in comparison with its previously reported 4-Br/4-Cl analogues. The crystal structure is stabilised by multiple supramolecular interactions of Cu₃⋯I and hydrogen/halogen bonding. The photophysical properties and supramolecular interactions are investigated experimentally/computationally for all three 4-halo complexes vis-à-vis relativistic effects.

Selective and rapid extraction of trace amount of gold from complex liquids with silver(I)-organic frameworks

The design of adsorbents for rapid, selective extraction of ultra-trace amounts of gold from complex liquids is desirable from both an environmental and economical point of view. However, the development of such materials remains challenging. Herein, we report the fabrication of two vinylene-linked two-dimensional silver(I)-organic frameworks prepared via Knoevenagel condensation. This material enables selective sensing of gold with a low limit of detection of 60 ppb, as well as selective uptake of ultra-trace gold from complex aqueous mixtures including distilled water with 15 competing metal ions, leaching solution of electronic waste (e-waste), wastewater, and seawater. The present adsorbent delivers a gold adsorption capacity of 954 mg g^-1, excellent selectivity and reusability, and can rapidly and selectively extract ultra-trace gold from seawater down to ~20 ppb (94% removal in 10 minutes). In addition, the purity of recovered gold from e-waste reaches 23.8 Karat (99.17% pure).

Gold nanocluster with AIE: A novel photodynamic antibacterial and deodorant molecule

Designing long-lasting yet high-efficiency antimicrobial and deodorant agents is an everlasting goal for environmental and public health. Here we present the design of AIE-featured Au nanoclusters (NCs) for visible-light-driven antibacterial and deodorant applications. Owing to the intriguing AIE traits, the good harvest of visible-light, and rich surface chemistry, the AIE-featured Au NCs unprecedentedly exhibit excellent visible-light-driven antibacterial activities against gram-positive (≥98.5%) and gram-negative bacteria (≥99.94%), which is resulted from their photodynamic producibility of abundant reactive oxygen species including O₂^•-, •OH and H₂O₂ via O₂ reduction and subsequent H₂O₂ oxidation. In addition, the Au NCs are demonstrated to be biocompatible, and easy to be deployed for downstream antibacterial and deodorant applications. For example, the Au NCs-modified domestic materials (e.g., latex, ceramic glaze, organic fiber, and clothings) achieve long-lasting antibacterial efficiency of 99% and deodorant efficiency of >97.9% under visible-light irradiation. This work may shed light on designing novel AIE-featured metal NCs with photodynamic antibacterial and deodorant functions, enabling metal NCs and corresponding downstream materials to step into the photodynamic antibacterial and deodorant era.

Enhanced Fluorescence with Tunable Color in Doped Diphosphine-Protected Gold Nanoclusters

Rational control of the luminescent properties of ligand-protected coinage metal clusters has long been pursued but remains challenging. Here we explore the crucial structural and electronic factors governing the fluorescence of a diphosphine-protected [Au₁₃(dppe)₅Cl₂]³⁺ cluster by time-dependent density functional theory calculations. By substituting the central Au atom with group 5 to group 11 transition metal atoms, the emission wavelength is adjustable from red to blue, accompanied by enhanced fluorescence intensity compared with the undoped cluster. The evolution of light-emitting behavior upon doping and the corresponding roles of the dopant, Au cage, ligands, and their interplay are interpreted at the electronic structure level. In particular, strong dopant-Au cage interaction associated with large electron-hole overlap on the dopant are is a key factor to endow large emission energy and intensity. These theoretical results provide vital guidance for designing atomically precise nanoclusters with visible fluorescence and high quantum yield for practical uses.

A Reinterpretation of the Imidazolate Au(I) Cyclic Trinuclear Compounds Reactivity with Iodine and Methyl Iodide with the Perspective of the Inverted Ligand Field Theory

Coinage metal cyclic trinuclear compounds (CTCs) are an emerging class of metal coordination compounds that are valuable for many fine optoelectronic applications, even though the reactivity dependence by the different bridging ligands remains somewhat unclear. In this work, to furnish some hints to unravel the effect of substituents on the chemistry of Au(I) CTCs made of a specific class of bridging ligand, we have considered two imidazolate Au(I) CTCs and the effect of different substituents on the pyrrolic N atoms relative to classic metal oxidations with I₂ or by probing electrophilic additions. Experimental suggestions depict a thin borderline between the addition of MeI to the N-methyl or N-benzyl imidazolyl CTCs, which afford the oxidized CTC in the former and the ring opening of the CTC and the formation of carbene species in the latter. Moreover, the reactions with iodine yield to the oxidation of the metal centers for the former and just of a metal center in the latter, even in molar excess of iodine. The analysis of the bond distances in the X-ray crystal structures of the oxidized highlights that Au(III)-C and Au(III)-N bonds are longer than observed for Au(I)–C and Au(I)–N bonds, as formally not expected for Au(III) centers. Computational studies converge on the attribution of these discrepancies to an additional case of inverted ligand field (ILF), which solves the question with a new interpretation of the Au(I)–ligand bonding in the oxidized CTCs, which furnishes a new interpretation of the Au(I)-ligand bonding in the oxidized CTCs, opening a discussion about addition/oxidation reactions. Finally, the theoretical studies outputs depict energy profiles that are compatible with the experimental results obtained in the reaction of the two CTCs toward the addition of I₂, MeI, and HCl.

A revisitation of some classic oxidation reactions of gold centers in cyclic trinuclear compounds (CTCs) provides experimental results leading to the opportunity to delineate the effect of imidazole substituents in different outcomes from the reactions of CTCs with I₂ or MeI. Moreover, with the match between experimental and theoretical results, a new interpretation of the oxidation states of tetracoordinate gold as cases of inverted ligand field (ILF) is discussed.

Enhancing photoluminescence efficiency of atomically precise copper(I) nanoclusters through solvent-induced structural transformation

Atomically precise copper(I) nanoclusters (CuNCs) with high photoluminescence (PL) efficiency and relatively short lifetime could be promising non-precious metal-based phosphorescent emitters for organic light-emitting diodes (OLEDs), but the synthesis of...

Strongly phosphorescent and water-soluble gold(I)-silver(I)-cysteine nanoplatelets via versatile small biomolecule cysteine-assisted synthesis for intracellular hypochlorite detection

In biological systems, abnormal levels of hypochlorite (ClO^-) could result in cell dysfunctions. Herein, we report a facile, one-step and green approach based on the versatile small biomolecule cysteine both serving as reducing agent and ligand for synthesizing the strongly photoluminencent and water-soluble Au(I)-Ag(I)-cysteine complexes nanoplatelets (Au(I)-Ag(I)-Cys nanoplatelets) for intracellular hypochlorite detection. Multiple spectroscopic and microscopical tools have been used to characterize the resultant Au(I)-Ag(I)-Cys nanoplatelets. It was found that with the cysteine-assisted synthesis approach, the Ag(I) doping to the Au(I) complexes could form the supramolecular organometallic nanoplatelets. Inside, the Au(I)-Ag(I) metallophilic interactions showing an Au to Ag charge transfer property were formed, thereby enhancing the photoluminescence (PL) intensity via the charge transfer from the bioligand's S to the metal-metal center. The quantum yield (QY) was measured to show a maximum 16-fold enhancement (i.e., from 0.85 to 13.8%). Interestingly, in the presence of ClO^-, the metal-thiolate ligand structure of the as-synthesized Au(I)-Ag(I)-Cys nanoplatelets could be oxidatively damaged, causing the PL quenching, thereby producing the effect of biorecognition towards ClO^- anions. The ClO^--induced PL quenching produced two linear regions at ClO^- concentrations of 0.01-5.0 μM and 5.0-1000 μM with a limit of detection (LOD) of 8.0 nM (S/N = 3). The ClO^--induced PL quenching was specific over the other typical reactive oxygen species (ROS) and the potential interfering substances in biological samples. In addition, the Au(I)-Ag(I)-Cys nanoplatelets had good biocompatibility. Thus, they could be further developed as a biosensor for detecting endogenous ClO^- anions in living cells.

An insight, at the atomic level, into the polarization effect in controlling the morphology of metal nanoclusters

The polarization effect has been a powerful tool in controlling the morphology of metal nanoparticles. However, a precise investigation of the polarization effect has been a challenging pursuit for a long time, and little has been achieved for analysis at the atomic level. Here the atomic-level analysis of the polarization effect in controlling the morphologies of metal nanoclusters is reported. By simply regulating the counterions, the controllable transformation from Pt₁Ag₂₈(S-PhMe₂)_x(S-Adm)_18−x(PPh₃)₄ (x = 0–6, Pt1Ag28-2) to Pt₁Ag₂₄(S-PhMe₂)₁₈ (Pt1Ag24) with a spherical configuration or to Pt₁Ag₂₈(S-Adm)₁₈(PPh₃)₄ (Pt1Ag28-1) with a tetrahedral configuration has been accomplished. In addition, the spherical or tetrahedral configuration of the clusters could be reversibly transformed by re-regulating the proportion of counterions with opposite charges. More significantly, the configuration transformation rate has been meticulously manipulated by regulating the polarization effect of the ions on the parent nanoclusters. The observations in this paper provide an intriguing nanomodel that enables the polarization effect to be understood at the atomic level.

Based on the inter-conversion between Pt₁Ag₂₄(SR)₁₈ and Pt₁Ag₂₈(SR)₁₈(PPh₃)₄, an insight into the polarization effect in controlling the morphology of metal nanoparticles is presented.