Tian-Yi Luo

Orthogonal Ternary Functionalization of a Mesoporous Metal–Organic Framework via Sequential Postsynthetic Ligand Exchange

A sequential postsynthetic ligand exchange process was used to prepare a series of mono-, di-, and trifunctionalized mesoporous metal-organic frameworks (MOFs). Using this process, orthogonal functional groups were installed and thereafter postsynthetically modified with dye and quencher molecules. Microspectrophotometry studies were used to determine the distribution of the two orthogonal functional groups within the MOF crystals.

Silicon Nanoparticles with Surface Nitrogen: 90% Quantum Yield with Narrow Luminescence Bandwidth and the Ligand Structure Based Energy Law

Silicon nanoparticles (NPs) have been widely accepted as an alternative material for typical quantum dots and commercial organic dyes in light-emitting and bioimaging applications owing to silicons intrinsic merits of least toxicity, low cost, and high abundance. However, to date, how to improve Si nanoparticle photoluminescence (PL) performance (such as ultrahigh quantum yield, sharp emission peak, high stability) is still a major issue. Herein, we report surface nitrogen-capped Si NPs with PL quantum yield up to 90% and narrow PL bandwidth (full width at half-maximum (fwhm) ≈ 40 nm), which can compete with commercial dyes and typical quantum dots. Comprehensive studies have been conducted to unveil the influence of particle size, structure, and amount of surface ligand on the PL of Si NPs. Especially, a general ligand-structure-based PL energy law for surface nitrogen-capped Si NPs is identified in both experimental and theoretical analyses, and the underlying PL mechanisms are further discussed.

Tailoring the Structure of 58-Electron Gold Nanoclusters: Au103S2(S-Nap)41 and Its Implications

We report the synthesis and crystal structure determination of a gold nanocluster with 103 gold atoms protected by 2 sulfidos and 41 thiolates (i.e., 2-naphthalenethiolates, S-Nap), denoted as Au103S2(S-Nap)41. The crystallographic analysis reveals that the thiolate ligands on the nanocluster form local tetramers by intracluster interactions of C-H···π and π···π stacking. The herringbone pattern formation via intercluster interactions is also observed, which leads to a linearly connected zigzag pattern in the single crystal. The kernel of the nanocluster is a Marks decahedron of Au79, which is the same as the kernel of the previously reported Au102(pMBA)44 (pMBA = -SPh-p-COOH); this is a surprise given the much bulkier naphthalene-based ligand than pMBA, indicating the robustness of the decahedral structure as well as the 58-electron configuration. Despite the same kernel, the surface structure of Au103 is quite different from that of Au102, indicating the major role of ligands in constructing the surface structure. Other implications from Au103 and Au102 include (i) both nanoclusters show similar HOMO-LUMO gap energy (i.e., Eg ≈ 0.45 eV), indicating the kernel is decisive for Eg while the surface is less critical; and (ii) significant differences are observed in the excited-state lifetimes by transient absorption spectroscopy analysis, revealing the kernel-to-surface relaxation pathway of electron dynamics. Overall, this work demonstrates the ligand-effected modification of the gold-thiolate interface independent of the kernel structure, which in turn allows one to map out the respective roles of kernel and surface in determining the electronic and optical properties of the 58e nanoclusters.

Rare Earth pcu Metal–Organic Framework Platform Based on RE4(μ3-OH)4(COO)62+ Clusters: Rational Design, Directed Synthesis, and Deliberate Tuning of Excitation Wavelengths

The Td point group symmetry of rare earth (RE3+) metal clusters RE4(μ3-OH)4(COO)62+ makes them attractive building blocks for creating metal-organic frameworks (MOFs) with controllable topologies. Herein, we describe the design and synthesis of a series of isoreticular MOFs featuring pcu topology [MOF-1114(RE) and MOF-1115(RE)] with variable rare earth metal ions (RE3+ = Y3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+) and linear amino-functionalized dicarboxylate linkers of different lengths. In total, we report 22 MOFs that vary in both composition and structure yet share the same RE4(μ3-OH)4 cluster motif. We demonstrate that these pcu MOFs are cationic and that anion exchange can be used to affect the MOF properties. We also investigate the luminescence properties of a representative member of this MOF series [MOF-1114(Yb)] that exhibits near-infrared emission. We show that the excitation energy for Yb3+ sensitization can be carefully adjusted to lower energy via covalent postsynthetic modification at the amino group sites within the MOF.

Molecular “surgery” on a 23-gold-atom nanoparticle

Changes to surface motifs provide precise tailoring of nanoparticle properties. 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.

Shuttling single metal atom into and out of a metal nanoparticle

It has long been a challenge to dope metal nanoparticles with a specific number of heterometal atoms at specific positions. This becomes even more challenging if the heterometal belongs to the same group as the host metal because of the high tendency of forming a distribution of alloy nanoparticles with different numbers of dopants due to the similarities of metals in outmost electron configuration. Herein we report a new strategy for shuttling a single Ag or Cu atom into a centrally hollow, rod-shaped Au24 nanoparticle, forming AgAu24 and CuAu24 nanoparticles in a highly controllable manner. Through a combined approach of experiment and theory, we explain the shuttling pathways of single dopants into and out of the nanoparticles. This study shows that the single dopant is shuttled into the hollow Au24 nanoparticle either through the apex or side entry, while shuttling a metal atom out of the Au25 to form the Au24 nanoparticle occurs mainly through the side entry.Doping a metal nanocluster with heteroatoms dramatically changes its properties, but it remains difficult to dope with single-atom control. Here, the authors devise a strategy to dope single atoms of Ag or Cu into hollow Au nanoclusters, creating precise alloy nanoparticles atom-by-atom.

Programmable Topology in New Families of Heterobimetallic Metal–Organic Frameworks

Using diverse building blocks, such as different heterometallic clusters, in metal-organic framework (MOF) syntheses greatly increases MOF complexity and leads to emergent synergistic properties. However, applying reticular chemistry to syntheses involving more than two molecular building blocks is challenging and there is limited progress in this area. We are therefore motivated to develop a strategy for achieving systematic and differential control over the coordination of multiple metals in MOFs. Herein, we report the design and synthesis of a diverse series of heterobimetallic MOFs with different metal ions and clusters severally distributed throughout two or three inorganic secondary building units (SBUs). By taking advantage of the bifunctional isonicotinate linker and its derivatives, which can coordinatively distinguish between early and late transition metals, we control the assembly and topology of up to three different inorganic SBUs in one-pot solvothermal reactions. Specifically, M6(μ3-O) n(μ3-OH)8- n(CO2)12 (M = Zr4+, Hf4+, Dy3+) SBUs are formed along with metal-pyridyl complexes. By controlling the geometry of the metal-pyridyl complexes, we direct the overall topology to produce eight new MOFs with fcu, ftw, and previously unreported trinodal pfm crystallographic nets.

CCDC 1840494: Experimental Crystal Structure Determination

Related Article: Chong Liu, Svetlana V. Eliseeva, Tian-Yi Luo, Patrick F. Muldoon, Stephane Petoud, Nathaniel L. Rosi||Chemical Science|||doi:10.1039/C8SC03168A

Modulating the hierarchical fibrous assembly of Au nanoparticles with atomic precision

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.Constructing nanoparticle assemblies with atomic precision remains a major challenge in nanoscience. Here, the authors realize atomic‐level control over the 1D, 2D and hierarchical 3D assembly of Au nanoparticles by modulating the site‐specific surface ligands and associated counterions.

A Correlated Series of Au/Ag Nanoclusters Revealing the Evolutionary Patterns of Asymmetric Ag Doping

Doping of metal nanoclusters is an effective strategy for tailoring their functionalities for specific applications. To gain fundamental insight into the doping mechanism, it is of critical importance to have access to a series of correlated bimetal nanoclusters with different doping levels and further reveal the successive transformations. Herein, we report asymmetric doping of Ag into an Au21 nanocluster to form a series of new Au/Ag bimetal nanoclusters and the effects of doping on the evolution of size, structure, and properties based upon X-ray crystallography and optical spectroscopy analyses. The asymmetric doping discovered in the series reveals two important rules. First, the heteroatom doping-induced kernel transformation mechanism is revealed, explaining the successive conversions from Au21(S-Adm)15 with an incomplete cuboctahedral kernel to Au20Ag1(S-Adm)15 with a complete cuboctahedral Au12Ag1 kernel and then to Au19Ag4(S-Adm)15 with an icosahedral Au10Ag3 kernel. The electron density accumulated on the central Au atom(s) is rationalized to force an expansion of radial metal-metal bond angles, which triggers the cuboctahedral-to-icosahedral kernel conversion. This mechanism is generalized by elucidating several other cases. Second, through comparison of a series of seven nanoclusters (all protected by adamantanethiolate), we find that the unit cell symmetry of their crystals is correlated with the symmetry of the clusters kernel. Specifically, we observe a sequential change from triclinic to monoclinic to trigonal unit cell in the series with increasing kernel symmetry. The kernel structure-dependent optical properties are also discussed.