Recently, metal nanoclusters (MNCs) emerged as a new class of luminescent materials and have attracted tremendous interest in the area of luminescence-related applications due to their excellent luminous properties (good photostability, large Stokes shift) and inherent good biocompatibility. However, the origin of photoluminescence (PL) of MNCs is still not fully understood, which has limited their practical application. In this mini-review, focusing on the origin of the photoemission emission of MNCs, we simply review the evolution of luminescent mechanism models of MNCs, from the pure metal-centered quantum confinement mechanics to ligand-centered p band intermediate state (PBIS) model via a transitional ligand-to-metal charge transfer (LMCT or LMMCT) mechanism as a compromise model.

The availability of a range of excited states has endowed low dimensional quantum nanostructures with interesting luminescence properties. However, the origin of photoluminescence emission is still not fully understood, which has limited its practical application. Here we judiciously manipulate the delicate surface ligand interactions at the nanoscale interface of a single metal nanocluster, the superlattice, and mesoporous materials. The resulting interplay of various noncovalent interactions leads to a precise modulation of emission colors and quantum yield. A new p-band state, resulting from the strong overlapping of p orbitals of the heteroatoms (O, N, and S) bearing on the targeting ligands though space interactions, is identified as a dark state to activate the triplet state of the surface aggregated chromophores. The UV-Visible spectra calculated by time-dependent density functional theory (TD-DFT) are in quantitative agreement with the experimental adsorption spectra. The energy level of the p-band center is very sensitive to the local proximity ligand chromophores at heterogeneous interfaces.

Molecules confined in the nanocavity and nanointerface exhibit rich, unique physicochemical properties, e.g., the chromophore in the β-barrel can of green fluorescent protein (GFP) exhibits tunable bright colors. However, the physical origin of their photoluminescence (PL) emission remains elusive. To mimic the microenvironment of the GFP protein scaffold at the molecule level, two groups of nanocavities were created by molecule self-assembly using organic chromophores and by organic functionalization of mesoporous silica, respectively. We provide strong evidence that structural water molecules confined in these nanocavities are color emitters with a universal formula of {X+ ) groups as an anchoring point, and that the efficiency of PL is strongly dependent on the stability of the main emitter centers of the structural hydrated hydroxide complex (OH − •H 2 O), which is a key intermediate to mediate electron transfer dominated by proton transfer at confined nanospace. Further controlled experiments and combined characterizations by time-resolved steady-state and ultrafast transient optical spectroscopy unveil an unusual multichannel radiative and/or nonradiative mechanism dominated by quantum transient states with a distinctive character of topological excitation. The finding of this work underscores the pivotal role of structurally bound H 2 O in regulating the PL efficiency of aggregation-induced emission luminogens and GFP.

Intrinsically, free water molecules are colorless liquid. If it is colorful, why and how does it emit the bright colors? We provided direct evidences that, when water was trapped into...

Surface states—the electronic states emerging as a solid material terminates at a surface—are usually vulnerable to contaminations and defects. This fundamental limitation has prohibited systematic studies of the potential role of surface states in surface reactions and catalysis, especially in more realistic environments. We use the selective reduction of 4-Nitrophenol on silver-covered dendritic mesoporous silica nanospheres (DMSNs) as a prototype example, and show that the dynamic intermediate surface states (DISS) spatially formed by spin orbital coupling (SOC) in singly hydrated hydroxyl complex can significantly enhance the adsorption energy of both 4-Nitrophenol and BH4- anions, by promoting different directions of static electron transfer. The concept of DISS as an electron bath may lead to new design principles beyond the conventional d-band theory of heterogeneous catalysis.

Mesoporous silica nanoparticles with varied morphologies and pore structures were synthesized on the kilogram scale using cetyltrimethylammonium bromide and an anionic surfactant as co-templates.

It has been widely accepted that decreasing the pH value could enhance the reactivity of 4-Nitrophenol (4-NP) reduction accompanied with the pillage of H2, but excess hydrogen generation is wasteful and easy to lead to safety problems. Herein, we show that, contrast to previously reported results, interfacial adsorbed hydroxyl significantly promotes reduction of 4-NP using Ag-based nanoparticles (NPs) confined in dendritic mesoporous silica nanospheres (Ag@DMSNs) as a model catalyst at medium concentration of sodium hydroxide (NaOH). We provide strong evidences that adsorptive 4-NP and hydroxyl could spatially interact to form an intermediate state through p-p overlapping of O atoms at nanoscale interface of Ag NPs, which leads to electron redistribution and accelerates N=O bonds cleavage, and consequently accelerates the reduction of 4-NP. The findings of this work demonstrate that improving the catalytic performance can be holistically achieved through manipulating the weak interactions between reactant and enthetic species on the molecule level. Introduction: 4-Aminophenol (4-AP), the reduction product of 4-NP, is a potent intermediate for the manufacture of pharmaceuticals and dyes. 1 However, without the catalyst, the hydrogenation of 4-NP to 4-AP by NaBH4 is kinetically restricted due to kinetic barriers resulting from the large potential difference between 4-NP and BH4-. 2 In recent years, noble metal nanoparticles (MNPs) have been discovered to exhibit high catalytic activity for selective reduction of 4-NP in the presence of NaBH4, such as Ag NPs, 3 Au NPs, 4 Pd NPs, 5 and Pt NPs. 6 Among these MNPs catalysts, Ag-based catalysts are distinctive (easy preparation, relatively low cost, less toxicity, high activity and good stability) and have been extensively utilized for 4-NP reduction. 7 However, it should be noted that MNPs catalysts are susceptible to suffer from aggregating due to the Van der Waals forces and high surface free energy. 8 For 4-NP reduction on Ag-based catalysts, the formation of large metal particles largely affects the catalytic activity and reusable performance. Accordingly, silver nanoparticles anchored through organic (such as polymers and DNA) 9 or inorganic (such as glasses, metal oxides and zeolites) 10 templates have been proposed to address the above issues. Among them, dendritic mesoporous silica nanospheres (DMSNs) composed of cage-like spherical nanopores have been confirmed as a unique confinement matrix for the encapsulation of MNPs and enable their application in catalysis. 11 The catalytic performance of MNPs catalysts strongly depends on their microstructure (catalyst composition, exposed crystal face, defect sits, adsorbed species, etc.) and reaction microenvironment (pressure, solvent, pH etc.). Although the reduction of 4-NP is intensively studied as a model reaction, the reaction mechanism is not yet fully comprehended. It is widely accepted that the reduction of 4-NP follows a multistep reduction process and the 4-hydroxylaminophenol (Hx) is a relative stable inte...

Concerted electron and proton transfer is a key step for the reversible conversion of molecular hydrogen in both heterogeneous nanocatalysis and metalloenzyme catalysis. However, its activation mechanism involving electron and...