Structural Water Molecules Confined in Soft and Hard Nanocavities as Bright Color Emitters

Abstract

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.

Origin of the Bright Photoluminescence of Thiolate-protected Gold Nanoclusters: Confined Structural Water Molecules as Real Emitters

“…The emission properties can be tuned by the solvent [68], thermal annealing treatment [77] and cations [19,78,79], etc. which was highly related to the hydration state of silver NCs [20,80], and the emission was unambiguously attributed to the behavior of structural water molecules (SWs) confined in nanoscale interface and/or space [67][68][69][70][71]. Based on the fundamentals of SWs, these elusive results as above discussed can be well understood.…”

“…Obviously, the bonding strength of σ' bonds perpendicular to the interface determines the energy and profile of π' and π'' bonds parallel to the interface direction, which regulates the spectral characteristics of steady-state absorption and emission spectra of Au NCs or aggregates (Figure 3). Differing from the d-band center theory for transition metals, a simple physical faramework named as the "p band intermidate states (PBIS)" model is proposed to illuminate the principles for modulating the PL properties of low-dimensional quantum nanodots, we also called it p-band model for simplicity [66,69]. Owing to the transient occupancy of p orbitals, the bonding electrons was delocalized at four region of electron interaction (two σ' bond, one π' bond and one π'' bond) as shown in the schematic electron cloud diagram (Figure 4b, bottom), imaging the electron pool at the nanosale interface.…”

“…We can conclude that both quantum size effect or AIE effect is not a personality for a certain type of materials or molecules but a common feature for luminescent materials, and metal-thiolate complexes bound on metallic core in good solvent or aggregated in the poor solvent can emit identical phosphorescence [52], which established a connection between quantum size effect and AIE effect. We would ask whether the common luminescent properties may not originated from the quantum dots or aggregates itself but a common species, such as ubiquitous water molecules suggested and investigated in our previous researches [66][67][68][69][70][71], adsorbed or confined in the nanoscale interface and/or space? Understanding the luminescent fundamentals of metal(I)-thiolate complexes with AIE characteristics can give better insight to both quantum size effect and AIE effect on luminescence for low-dimension quantum dots and AIEgens, respectively.…”

High Efficient and Stable Thiol-Modified Dendritic Mesoporous Silica Nanospheres Supported Gold catalysts for Gas-phase Selective Oxidation of Benzyl Alcohol with Ultra-Long Lifetime

“…For clarity, propyl segments were omitted. benzyl alcohol molecule, [42][43][44][45][46][47][48] and finally finished the catalytic cycle for the oxidation (Step 6).…”

Dynamic Pt-OH-•H2O-Ag Species Mediate Synergetic Electron and Proton Transfer for Catalytic Hydride Reduction of 4-Nitrophenol at Confined Nanoscale Interface

“…Recently, relying on the combined characterizations of absorption, excitation and photoluminescence spectrum and femto-second time-resolved ultra-fast transient absorption technique, an ensemble of dynamic intermediate states with π bonding characteristic, so called the p band states, stemming from the spatial overlapping of p orbitals of oxygen atoms in the hydrous hydroxyl (OH -) and/or oxy species at confined metal or nonmetal nano-interface, was unambiguously identified, which can be alternative radiation decay pathway for the electron transfer of excited states (33)(34)(35)(36). More recently, the p band dominated interfacial electron transfer theory successfully elucidates the reaction mechanism of several typical probe reactions at mono-metal catalysts (21,22,31,37).…”