Fabrication of Water-Soluble, Green-Emitting Gold Nanoclusters with a 65% Photoluminescence Quantum Yield via Host–Guest Recognition

Abstract

Metal nanoclusters (NCs) as a new type of fluorescent material have been extensively explored because of their attractive set of features such as their ultrafine size, low toxicity, and excellent photostability. However, little progress has been made in producing water-soluble, homogeneous, and ultrabright metal NCs. In this study, gold NCs (AuNCs) with a photoluminescence quantum yield (QY) as high as 65% are synthesized in water through a simple blending route. Weak emission is observed from the 6-aza-2-thiothymine-protected AuNCs (ATT-AuNCs); however, the fluorescence intensity can be prominently enhanced by introducing L-arginine (Arg) into the capping layer. The fluorescence enhancement mechanism is systematically investigated by the measurements of ultraviolet−visible absorption spectroscopy, photoluminescence spectroscopy, fluorescence lifetime spectroscopy, transmission electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, 1 H nuclear magnetic resonance, and calculations from density functional theory, with results isolating the vital role of the ligand shell and ruling out the effect of the gold core. The supramolecular host−guest assemblies formed between ATT capped on the gold core and the guanidine group of Arg make the capping ligands of ATT rigid. Subsequently, the intramolecular vibration and rotation of ATT are greatly suppressed, which reduce the nonradiative relaxation of excited states and, as a result, predominantly increase the luminescence QY of ATT-AuNCs. Further experiments demonstrate that a small change in guanidine substituents can arouse obvious changes in the photoluminescence features of NCs. We envision that this work will substantively contribute to the process of developing efficient synthetic routes to high-quality metal NCs.

Efficient and Monochromatic Electrochemiluminescence of Aqueous‐Soluble Au Nanoclusters via Host–Guest Recognition

“…[18] Thestrategy to enhance the ECL of the AuNCs via improving their shell rigidity provides an alternative to the strategy via covalent attachment of co-reactants to the AuNCs. [18] Thestrategy to enhance the ECL of the AuNCs via improving their shell rigidity provides an alternative to the strategy via covalent attachment of co-reactants to the AuNCs.…”

“…[18] As shown in Figure 1, the ATT-AuNCs displayed two well-defined absorption processes centered around 423 and 485 nm (dashed curve a) and demonstrated monochromatic PL around 532 nm with af ull width at half-maximum (FWHM) of 36 nm (solid curve a) and aP Lq uantum yield of 0.03 %. Because the rigid host-guest assemblies that are formed via hydrogen bonding between the ATToft he ATT-AuNCs and the guanidine group of ARG can hinder the intra- molecular vibration and rotation of ATTand thereby reduce the non-radiative relaxation of excited states, [18] the ARG/ ATT-AuNCs displayed ad ramatically enhanced PL of as imilar spectral nature to the ATT-AuNCs (solid curves a, b). Because the rigid host-guest assemblies that are formed via hydrogen bonding between the ATToft he ATT-AuNCs and the guanidine group of ARG can hinder the intra- molecular vibration and rotation of ATTand thereby reduce the non-radiative relaxation of excited states, [18] the ARG/ ATT-AuNCs displayed ad ramatically enhanced PL of as imilar spectral nature to the ATT-AuNCs (solid curves a, b).…”

“…[17] Inspired by these achievements,t he formation of rigid hostguest assemblies around the AuNCs was adopted herein to screen electrochemiluminophores with enhanced performance for the first time.6-aza-2-thiothymine(ATT)-protected AuNCs (ATT-AuNCs) and l-arginine (ARG) were chosen as models,s ince the host-guest recognition between ATTa nd ARG could form ARG/ATT-AuNCs with rigid host-guest assemblies on the outside (Figure 1, inset D). [18] TheA TT-AuNCs and ARG/ATT-AuNCs were prepared according to reported procedures with slight modifications (see Supporting Information). [18] As shown in Figure 1, the ATT-AuNCs displayed two well-defined absorption processes centered around 423 and 485 nm (dashed curve a) and demonstrated monochromatic PL around 532 nm with af ull width at half-maximum (FWHM) of 36 nm (solid curve a) and aP Lq uantum yield of 0.03 %.…”

Shortwave Infrared in Vivo Imaging with Gold Nanoclusters

“…17,25,33–35 In our case, the extended ligand shell contributes to the blue-shifted luminescence and higher QY, which is probably due to rigidification of the gold shell structure that contains several Au–S motifs. 13,36 To get the highest SWIR signal from Au NCs, we need to balance a higher QY but a shorter emission maximum with a lower QY but a longer emission maximum. Au NCs (1:1) treated with extra ligands (Figure 2a) provide the highest brightness in the SWIR, and we use these to demonstrate in vivo SWIR imaging.…”

Amphiphilicity Regulation of AgI Nanoclusters: Self‐Assembly and Its Application as a Luminescent Probe

“…[7][8][9][10] Although metal NCs have excellent luminescence in the solid state, they perform luminescence quenching in the single-molecule state,which limits their applications.Therefore, to improve the metalN Cs' fluorescence properties in solution state,s tudies about regulation of the luminescence properties of metal NCs have emergedr ecently. [11][12][13][14][15][16] Severalm ethods have been reported to enhance the luminescence of NCs in solution,s uch as ap hase-transfer method, regulation of the pH of the system,and inducing the formation of aggregates to enhancet he luminescence of the system. [17,18] For example, Wang et al reportedafacile methodf or the preparation of highly luminescent and stableC uN Cs by adjusting the pH value, and stableC uN Cs with aq uantum yield of 16.6 %w ere obtained.…”