Red-NIR luminescence of Mo6 monolayered assembly directly anchored on Au(001)

Octahedral molybdenum iodide clusters with pyrazole or pyrazolate ligands

Due to the combination of useful physicochemical properties (luminescence, X-ray contrast, etc.), octahedral molybdenum halide cluster complexes [Mo6X8L6]n have been the subject of active investigation during the last decades. The most common methods for synthesizing new compounds with organic ligands involve the use of silver salts of organic acids or the substitution of terminal methylate ligands. However, these methods often necessitate the use of special conditions, such as an inert atmosphere, absolute solvents, and silver salts, which can be costly. In contrast, aqua-hydroxo complexes formed by hydrolysis of many complexes are considered final unreactive products, despite the tendency for them to form. This work proposes a simple and affordable method for the preparation of hexaaqua and hexahydroxo iodide clusters of molybdenum from [Mo6I14]2- in a single step. Furthermore, the possibility of using such compounds as starting complexes for the synthesis of clusters with organic ligands such as pyrazole is discussed. The paper presents synthetic approaches, detailed characterization both in solid and in solution, and a study of the reactivity and luminescence properties of the obtained compounds.

Designed metal-organic π-clusters combining the aromaticity of the metal cluster and ligands for a third-order nonlinear optical response

The pivotal role of clusters and aromaticity in chemistry is undeniable, but there remains a gap in systematically understanding the aromaticity of metal-organic clusters. Herein, this article presents a novel metal-organic π-cluster, melding both metal-organic chemistry and aromaticity, to guide the construction of structurally stable Os-organic π-clusters. An in-depth analysis of these clusters reveals their bonding attributes, π-electronic composition, and origins of aromaticity, thereby confirming their unique metal-organic π-cluster properties. Furthermore, the Os5 cluster exhibits a promising third-order nonlinear optical (NLO) response, attributable to its narrow band gap and uniform electron/hole distribution, suggesting its potential as an optical switching material. This research introduces a fresh perspective on clusters, centered on delocalization, and broadens the domain of aromaticity studies. It also presents a novel method for designing efficient third-order NLO materials through consideration of the structure-activity relationship.

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

Phosphorescence, characterized by luminescent lifetimes significantly longer than that of biological autofluorescence under ambient environment, is of great value for biomedical applications. Academic evidence of fluorescence imaging indicates that virtually all imaging metrics (sensitivity, resolution, and penetration depths) are improved when progressing into longer wavelength regions, especially the recently reported second near-infrared (NIR-II, 1000-1700 nm) window. Although the emission wavelength of probes does matter, it is not clear whether the guideline of "the longer the wavelength, the better the imaging effect" is still suitable for developing phosphorescent probes. For tissue-specific bioimaging, long-lived probes, even if they emit visible phosphorescence, enable accurate visualization of large deep tissues. For studies dealing with bioimaging of tiny biological architectures or dynamic physiopathological activities, the prerequisite is rigorous planning of long-wavelength phosphorescence, being aware of the cooperative contribution of long wavelengths and long lifetimes for improving the spatiotemporal resolution, penetration depth, and sensitivity of bioimaging. In this Review, emerging molecular engineering methods of room-temperature phosphorescence are discussed through the lens of photophysical mechanisms. We highlight the roles of phosphorescence with emission from visible to NIR-II windows toward bioapplications. To appreciate such advances, challenges and prospects in rapidly growing studies of room-temperature phosphorescence are described.

From Solid-State Cluster Compounds to Functional PMMA-Based Composites with UV and NIR Blocking Properties, and Tuned Hues

New nanocomposite materials with UV-NIR blocking properties and hues ranging from green to brown were prepared by integrating inorganic tantalum octahedral cluster building blocks prepared via solid-state chemistry in a PMMA matrix. After the synthesis by the solid-state chemical reaction of the K₄[{Ta₆Brⁱ₁₂}Br^a₆] ternary halide, built-up from [{Ta₆Brⁱ₁₂}Br^a₆]^4- anionic building blocks, and potassium cations, the potassium cations were replaced by functional organic cations (Kat⁺) bearing a methacrylate function. The resulting intermediate, (Kat)₂[{Ta₆Brⁱ₁₂}Br^a₆], was then incorporated homogeneously by copolymerization with MMA into transparent PMMA matrices to form a brown transparent hybrid composite Ta@PMMA_brown. The color of the composites was tuned by controlling the charge and consequently the oxidation state of the cluster building block. Ta@PMMA_green was obtained through the two-electron reduction of the [{Ta₆Brⁱ₁₂}Br^a₆]^2- building blocks from Ta@PMMA_brown in solution. Indeed, the control of the oxidation state of the Ta₆ cluster inorganic building blocks occurred inside the copolymer, which not only allowed the tuning of the optical properties of the composite in the visible region but also allowed the tuning of its UV and NIR blocking properties.

Surface Plasmon Tunability of Core-Shell Au@Mo6 Nanoparticles by Shell Thickness Modification

Plasmon resonances of noble metal nanoparticles are used to enhance light-matter interactions in the nanoworld. The nanoparticles' optical response depends strongly on the dielectric permittivity of the surrounding medium. We show that the plasmon resonance energy of core-shell Au@Mo₆ nanoparticles can be tuned from 2.4 to 1.6 eV by varying the thickness of their Mo₆ cluster shells between zero and 70 nm, when the core diameter is fixed at 100 nm. We probe their plasmonic response by performing nanometer-resolution plasmon mapping on individual nanoparticles, using electron energy-loss spectroscopy inside a transmission electron microscope. Our experimental results are corroborated by numerical simulations performed using boundary element methods. The simulations predict a similar dependency for the extinction energy, showing that this effect could also be observed by light-optical experiments outside the electron microscope, although limited by the size distribution of the nanoparticles in solution and the substantial scattering effects.

Evidence of the Ambipolar Behavior of Mo6 Cluster Iodides in All-Inorganic Solar Cells: A New Example of Nanoarchitectonic Concept

Ambipolar materials such as carbon nanotubes, graphene, or 2D transition metal chalcogenides are very attractive for a large range of applications, namely, light-emitting transistors, logic circuits, gas sensors, flash memories, and solar cells. In this work, it is shown that the nanoarchitectonics of inorganic Mo₆ cluster-based iodides enable to form thin films exhibiting photophysical properties that enable their classification as new members of the restricted family of ambipolar materials. Thus, the electronic properties of the ternary iodide Cs₂[{Mo₆I₈ⁱ}I₆^a] and those of thin films of the aqua-complex-based compound [{Mo₆I₈ⁱ}I₄^a(H₂O)₂^a]·xH₂O were investigated through an in-depth photoelectrochemical study. Once hole/electron pairs are created, the holes and electrons turn to be transported simultaneously in opposite directions, and their lifetimes exhibit similar values. The ambipolar properties were demonstrated via the integration of [{Mo₆I₈ⁱ}I₄^a(H₂O)₂^a]·xH₂O as light harvesters in an all-solid solar cell. A significant photoresponse with a typical diode characteristic clearly provides evidence of the simultaneous transfer and transport of holes and electrons within the [{Mo₆I₈ⁱ}I₄^a(H₂O)₂^a]·xH₂O layer. The ambipolar behavior results, on the one hand, from the confinement of electrons imposed by the nanometric size of the molecular metal clusters and, on the other hand, from the poor electronic interactions between clusters in the solid state. Such molecular structure-based layers lead naturally to an intrinsic semiconducting behavior.

Revisiting properties of edge-bridged bromide tantalum clusters in the solid-state, in solution and vice versa: an intertwined experimental and modelling approach

Edge-bridged halide tantalum clusters based on the {Ta₆Br₁₂}⁴⁺ core have been the topic of many physicostructural investigations both in solution and in the solid-state. Despite a large number of studies, the fundamental correlations between compositions, local symmetry, electronic structures of [{Ta₆Brⁱ₁₂}L^a₆]^m+/n- cluster units (L = Br or H₂O, in solution and in the solid-state), redox states, and vibrational and absorption properties are still not well established. Using K₄[{Ta₆Brⁱ₁₂}Br^a₆] as a starting precursor (i: inner and a: apical), we have investigated the behavior of the [{Ta₆Brⁱ₁₂}Br^a₆]^4- cluster unit in terms of oxidation properties and chemical modifications both in solution (water and organic solvent) and after recrystallization. A wide range of experimental techniques in combination with quantum chemical simulations afford new data that allow the puzzling behavior of the cluster units in response to changes in their environment to be revealed. Apical ligands undergo changes like modifications of interatomic distances to complete substitutions in solution that modify noticeably the cluster physical properties. Changes in the oxidation state of the cluster units also occur, which modify significantly their physical properties, including optical properties, which can thus be used as fingerprints. A subtle balance exists between the number of substituted apical ligands and the cluster oxidation state. This study provides new information about the exact nature of the species formed during the transition from the solid-state to solutions and vice versa. This shows new perspectives on optimization protocols for the design of Ta₆ cluster-based materials.