Natural materials exhibit emergent mechanical properties as a result of their nanoarchitected, nanocomposite
structures with optimized hierarchy, anisotropy, and nanoporosity. Fabrication of such complex systems
is currently challenging because high-quality three-dimensional (3D) nanoprinting is mostly limited
to simple, homogeneous materials. We report a strategy for the rapid nanoprinting of complex structural
nanocomposites using metal nanoclusters. These ultrasmall, quantum-confined nanoclusters function
as highly sensitive two-photon activators and simultaneously serve as precursors for mechanical
reinforcements and nanoscale porogens. Nanocomposites with complex 3D architectures are printed,
as well as structures with tunable, hierarchical, and anisotropic nanoporosity. Nanocluster-polymer
nanolattices exhibit high specific strength, energy absorption, deformability, and recoverability. This
framework provides a generalizable, versatile approach for the use of photoactive nanomaterials in
additive manufacturing of complex systems with emergent mechanical properties.
Jin Tang, Ning Xu, An Ren, Liang Ma, Wenwu Xu, Zhongkang Han, Zijie Chen, Qi Li
Development of high-performance photoinitiator is the key to enhance the printing speed, structure resolution and product quality in 3D laser printing. Here, to improve the printing efficiency of 3D laser nanoprinting, we investigate the underlying photochemistry of gold and silver nanocluster initiators under multiphoton laser excitation. Experimental results and DFT calculations reveal the high cleavage probability of the surface S-C bonds in gold and silver nanoclusters which generate multiple radicals. Based on this understanding, we design several alkyl-thiolated gold nanoclusters and achieve a more than two-orders-of-magnitude enhancement of photoinitiation activity, as well as a significant improvement in printing resolution and fabrication window. Overall, this work for the first time unveils the detailed radical formation pathways of gold and silver nanoclusters under multiphoton activation and substantially improves their photoinitiation sensitivity via surface engineering, which pushes the limit of the printing efficiency of 3D laser lithography.
Jin Tang, Heyi Liang, An Ren, Liang Ma, Wei Hao, Yuqing Yao, Letian Zheng, Hanying Li,Qi Li We report a type of copper-nanocluster-polymer composites and showcase that their 3D nanolattices exhibit a superior combination of high strength, toughness, deformability, resilience and damage-tolerance. Notably, the strength and toughness of ultralight copper-nanocluster-polymer nanolattices in some cases surpass current best performers, including alumina, nickel, and other ceramic or metallic lattices at low densities. Additionally, copper-nanocluster-polymer nanolattices are super-resilient, crack-resistant, and one-step printed under ambient condition which can be easily integrated into sophisticated microsystems as highly effective internal protectors. Our findings suggest that, unlike traditional nanocomposites, the laser-induced interface and the high fraction of ultrasmall Cu 15 nanoclusters as crosslinking junctions contribute to the marked nonlinear elasticity of copper-nanocluster-polymer network, which synergizes with the lattice-topology effect and culminates in the exceptional mechanical performance.
Compared to molecular chemistry, nanochemistry is still far from being capable of tailoring particle structure and functionality at an atomic level. Numerous effective methodologies that can precisely tailor specific groups in organic molecules without altering the major carbon bones have been developed, but for nanoparticles, it is still extremely difficult to realize the atomic-level tailoring of specific sites in a particle without changing the structure of other parts (for example, replacing specific surface motifs and deleting one or two metal atoms). This issue severely limits nanochemists from knowing how different motifs in a nanoparticle contribute to its overall properties. We demonstrate a site-specific "surgery" on the surface motif of an atomically precise 23-gold-atom [Au23(SR)16]- nanoparticle by a two-step metal-exchange method, which leads to the "resection" of two surface gold atoms and the formation of a new 21-gold-atom nanoparticle, [Au21(SR)12(Ph2PCH2PPh2)2]+, without changing the other parts of the starting nanoparticle structure. This precise surgery of the nanocluster reveals the different reactivity of the surface motifs and the inner core: the least effect of surface motifs on optical absorption but a distinct effect on photoluminescence (that is, a 10-fold enhancement of luminescence after the tailoring). First-principles calculations further reveal the thermodynamically preferred reaction pathway for the formation of [Au21(SR)12(Ph2PCH2PPh2)2]+. This work constitutes a major step toward the development of atomically precise, versatile nanochemistry for the precise tailoring of the nanocluster structure to control its properties.
The origin of the near-infrared photoluminescence (PL) from thiolate-protected gold nanoclusters (Au NCs, <2 nm) has long been controversial, and the exact mechanism for the enhancement of quantum yield (QY) in many works remains elusive. Meanwhile, based upon the sole steady-state PL analysis, it is still a major challenge for researchers to map out a definitive relationship between the atomic structure and the PL property and understand how the Au(0) kernel and Au(I)–S surface contribute to the PL of Au NCs. Herein, we provide a paradigm study to address the above critical issues. By using a correlated series of “mono-cuboctahedral kernel” Au NCs and combined analyses of steady-state, temperature-dependence, femtosecond transient absorption, and Stark spectroscopy measurements, we have explicitly mapped out a kernel-origin mechanism and clearly elucidate the surface–structure effect, which establishes a definitive atomic-level structure–emission relationship. A ∼100-fold enhancement of QY is realized via suppression of two effects: (i) the ultrafast kernel relaxation and (ii) the surface vibrations. The new insights into the PL origin, QY enhancement, wavelength tunability, and structure–property relationship constitute a major step toward the fundamental understanding and structural-tailoring-based modulation and enhancement of PL from Au NCs.
Deciphering the complicated excited-state process is critical for the development of luminescent materials with controllable emissions in different applications. Here we report the emergence of a photo-induced structural distortion accompanied by an electron redistribution in a series of gold nanoclusters. Such unexpected slow process of excited-state transformation results in near-infrared dual emission with extended photoluminescent lifetime. We demonstrate that this dual emission exhibits highly sensitive and ratiometric response to solvent polarity, viscosity, temperature and pressure. Thus, a versatile luminescent nano-sensor for multiple environmental parameters is developed based on this strategy. Furthermore, we fully unravel the atomic-scale structural origin of this unexpected excited-state transformation, and demonstrate control over the transition dynamics by tailoring the bi-tetrahedral core structures of gold nanoclusters. Overall, this work provides a substantial advance in the excited-state physical chemistry of luminescent nanoclusters and a general strategy for the rational design of next-generation nano-probes, sensors and switches.
The ability to modulate nanoparticle (NP) assemblies with atomic precision is still lacking, which hinders us from creating hierarchical NP organizations with desired properties. In this work, a hierarchical fibrous (1D to 3D) assembly of Au NPs (21-gold atom, Au21)is realized and further modulated with atomic precision via site-specific tailoring of the surface hook (composed of four phenyl-containing ligands with a counteranion). Interestingly, tailoring of the associated counterion significantly changes the electrical transport properties of the NP-assembled solids by two orders of magnitude due to the altered configuration of the interacting π–π pairs of the surface hooks. Overall, our success in atomic-level modulation of the hierarchical NP assembly directly evidences how the NP ligands and associated counterions can function to guide the 1D, 2D, and 3D hierarchical self-assembly of NPs in a delicate manner. This work expands nanochemists’ skills in rationally programming the hierarchical NP assemblies with controllable structures and properties.
