Gas-Phase Azide Functionalization of Carbon

Building Co16-N3-Based UiO-MOF to Expand Design Parameters for MOF Photosensitization

The construction of secondary building units (SBUs) in versatile metal-organic frameworks (MOFs) represents a promising method for developing multi-functional materials, especially for improving their sensitizing ability. Herein, we developed a dual small molecules auxiliary strategy to construct a high-nuclear transition-metal-based UiO-architecture Co16-MOF-BDC with visible-light-absorbing capacity. Remarkably, the N3 - molecule in hexadecameric cobalt azide SBU offers novel modification sites to precise bonding of strong visible-light-absorbing chromophores via click reaction. The resulting Bodipy@Co16-MOF-BDC exhibits extremely high performance for oxidative coupling benzylamine (~100 % yield) via both energy and electron transfer processes, which is much superior to that of Co16-MOF-BDC (31.5 %) and Carboxyl @Co16-MOF-BDC (37.5 %). Systematic investigations reveal that the advantages of Bodipy@Co16-MOF-BDC in dual light-absorbing channels, robust bonding between Bodipy/Co16 clusters and efficient electron-hole separation can greatly boost photosynthesis. This work provides an ideal molecular platform for synergy between photosensitizing MOFs and chromophores by constructing high-nuclear transition-metal-based SBUs with surface-modifiable small molecules.

Metal-Organic Framework Thin Films as Ideal Matrices for Azide Photolysis in Vacuum

Studies on reactions in solutions are often hampered by solvent effects. In addition, detailed investigation on kinetics is limited to the small temperature regime where the solvent is liquid. Here, we report the in situ spectroscopic observation of UV-induced photochemical reactions of aryl azides within a crystalline matrix in vacuum. The matrices are formed by attaching the reactive moieties to ditopic linkers, which are then assembled to yield metal-organic frameworks (MOFs) and surface-mounted MOFs (SURMOFs). These porous, crystalline frameworks are then used as model systems to study azide-related chemical processes under ultrahigh vacuum (UHV) conditions, where solvent effects can be safely excluded and in a large temperature regime. Infrared reflection absorption spectroscopy (IRRAS) allowed us to monitor the photoreaction of azide in SURMOFs precisely. The in situ IRRAS data, in conjunction with XRD, MS, and XPS, reveal that illumination with UV light first leads to forming a nitrene intermediate. In the second step, an intramolecular rearrangement occurs, yielding an indoloindole derivative. These findings unveil a novel pathway for precisely studying azide-related chemical transformations. Reference experiments carried out for solvent-loaded SURMOFs reveal a huge diversity of other reaction schemes, thus highlighting the need for model systems studied under UHV conditions.

Fast and Versatile Functionalization of Glassy Carbon

A rapid procedure for the functionalization of glassy carbon surfaces (GCSs) is disclosed. A three-step sequence of bromomethylation, azide displacement, and copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) allows ethynylated molecules to be attached covalently to the carbon surface through a methylene functional group. Redox-active ethynyl ferrocene and [Ru^II(Cl)(DMSO)(ethynyl-TPA)]¹⁺ (DMSO = dimethylsulfoxide; TPA = tris(2-pyridylmethyl)amine) are attached with high coverages as assessed by cyclic voltammetry, and the elemental composition of the surface is confirmed by X-ray photoelectron spectroscopy. In less than 1 h, surface coverages of 1 × 10¹⁴ molecules/cm² are possible that exhibit good durability in both acidic and basic media. Attached [Ru^II(Cl)(DMSO)(ethynyl-TPA)]¹⁺ catalytically oxidizes alcohols, yet the currents and potentials are less impressive compared to an attachment without the intervening methylene group. The advantages of this covalent attachment procedure for GCSs are its short reaction times, mild reaction conditions, and the use of standard laboratory reagents and glassware, allowing for many types of ethynylated molecules to be attached rapidly to the surface.

Replacing amine by azide: Dopamine azide polymerization triggered by sodium periodate

Polydopamine (PDA) have been widely described for a range of biomedical and surface engineering applications. However the structure of PDA remains elusive due to the insoluble nature of the polymer....

Graphitic C2N3: An Allotrope of g-C3N4 Containing Active Azide Pentagons as Metal-Free Photocatalyst for Abundant H2 Bubble Evolution

A g-C₃N₄ allotrope, a curved leaf-like graphitic C₂N₃ (g-C₂N₃) with an intrinsic spontaneous polarization electric field (ISPEF), has been constructed for efficient solar energy conversion into H₂ energy via photocatalytic H₂O splitting. The curved leaf-like π-delocalization g-C₂N₃ was composed of aromatic azide pentagons and normal triazine hexagons obtained by cycloaddition between -C≡N groups from dicyandiamide polymerization and azide from the heat-treated polypyrrole fibers. Under light irradiation (λ > 420 nm), photo-generated charges are driven to separate efficiently and transfer from bulk to active sites of the surface under ISPEF that is opposite to the Coulomb field. Consequently, without any cocatalyst, g-C₃N₄ allotrope demonstrates a very high H₂-production activity of 14.9 mmol g^-1 h^-1 accompanied by a lot of H₂ bubbles, which is 2.6 times of g-C₃N₄ loading with Pt. In comparison with the reported metal-free photocatalysts or those supported with noble metals, g-C₃N₄ allotrope (i.e., leaf-like g-C₂N₃) is confirmed to be the best metal-free photocatalyst for H₂O splitting into H₂ fuel so far. The contructed leaf-like g-C₂N₃ with SPEF supplies a suitable platform for solar energy conversion into H₂ fuel, which actively contributes to clean energy production.

Immobilization of molecular catalysts for artificial photosynthesis

Artificial photosynthesis offers a way of producing fuels or high-value chemicals using a limitless energy source of sunlight and abundant resources such as water, CO2, and/or O2. Inspired by the strategies in natural photosynthesis, researchers have developed a number of homogeneous molecular systems for photocatalytic, photoelectrocatalytic, and electrocatalytic artificial photosynthesis. However, their photochemical instability in homogeneous solution are hurdles for scaled application in real life. Immobilization of molecular catalysts in solid supports support provides a fine blueprint to tackle this issue. This review highlights the recent developments in (i) techniques for immobilizing molecular catalysts in solid supports and (ii) catalytic water splitting, CO2 reduction, and O2 reduction with the support-immobilized molecular catalysts. Remaining challenges for molecular catalyst-based devices for artificial photosynthesis are discussed in the end of this review.

Quantitative Effects of Disorder on Chemically Modified Amorphous Carbon Electrodes

Real materials are disordered. This disorder influences the properties of these materials and the chemical processes that occur at their interfaces. Gaining a molecular-level understanding of the underlying physical manifestations caused by disordered materials is crucial to unraveling and ultimately controlling the efficiency and performance of these materials in a range of energy-related devices. This understanding necessitates measurement techniques through which disorder can be detected, quantified, and monitored. However, such quantitative measurements are notoriously difficult, as effects often average out in ensemble measurements. In this work, we describe how a combination of electrochemical and spatially resolved surface spectroscopy measurements illuminate a molecular-level picture of disorder in materials. Using amorphous carbon as an intrinsically disordered material, we covalently attached a monolayer of ferrocene. Interfacial electron transfer across the amorphous carbon-ferrocene interface is highly sensitive to disruptions of order. By systematically varying linker properties and surface loadings, the influence of lateral interactions between nonuniformly distributed ferrocene headgroups on ensemble electrochemical measurements is demonstrated. Electrochemical and imaging data collectively indicate that conformational flexibility of the ferrocene moieties provides a mechanism to elude repulsive and unbalanced lateral interactions, while rigid linkages provide direct information about the underlying disorder of the material. This study is the first of its kind to quantify and visualize molecular disorder and heterogeneity with an experimental model accessed through ensemble measurements.

Copper(ii) accelerated azide–alkyne cycloaddition reaction using mercaptopyridine-based triazole ligands

We report the synthesis, characterization and catalytic performance of a series of copper(ii) complexes supported by mercaptopyridine based traizole ligands.

Surface Immobilization of Molecular Electrocatalysts for Energy Conversion

Electrocatalysts are critically important for a secure energy future, as they facilitate the conversion between electrical and chemical energy. Molecular catalysts offer precise control of structure that enables understanding of structure-reactivity relationships, which can be difficult to achieve with heterogeneous catalysts. Molecular electrocatalysts can be immobilized on surfaces by covalent bonds or through non-covalent interactions. Advantages of surface immobilization include the need for less catalyst, avoidance of bimolecular decomposition pathways, and easier determination of catalyst lifetime. This Minireview highlights surface immobilization of molecular electrocatalysts for reduction of O₂ , oxidation of H₂ O, production of H₂ , and reduction of CO₂ .

Green click synthesis of β-hydroxy-1,2,3-triazoles in water in the presence of a Cu(ii)–azide catalyst: a new function for Cu(ii)–azide complexes

A new method for preparing 1,2,3-triazols via a [3+2]-cycloaddition reaction is introduced. The effect of reaction temperature on the epoxide ring opening reactions is also investigated.

Anodic Methods for Covalent Attachment of Ethynylferrocenes to Electrode Surfaces: Comparison of Ethynyl Activation Processes

The electrochemical oxidation of ferrocenes having an H- or Li-terminated ethynyl group has been studied, especially as it relates to their covalent anchoring to carbon surfaces. The anodic oxidation of lithioethynylferrocene (1-Li) results in rapid loss of Li(+) and formation of the ethynyl-based radical FeCp(η(5)-C5H4)(C≡C), (1, Cp = η(5)-C5H5), which reacts with the electrode. Chemically modified electrodes (CMEs) were thereby produced containing strongly bonded, ethynyl-linked monolayers and electrochemically controlled multilayers. Strong attachments of ethynylferrocenes to gold and platinum surfaces were also possible. The lithiation/anodic oxidation process is a mirror analogue of the diazonium/cathodic reduction process for preparation of aryl-modified CMEs. A second method produced an ethynylferrocene-modified electrode by direct anodic oxidation of the H-terminated ethynylferrocene (1-H) at a considerably more positive potential. Both processes produced robust modified electrodes with well-defined ferrocene-based surface cyclic voltammetry waves that remained unchanged for as many as 10(4) scans. Ferrocene derivatives in which the ethynyl moiety was separated from the cyclopentadienyl ring by an ether group showed very similar behavior. DFT calculations were performed on the relevant redox states of 1-H, 1-Li, and 1, with emphasis on the ferrocenyl vs ethynyl character of their high valence orbitals. Whereas the HOMOs of both 1-H and 1-Li have some ethynyl character, the SOMOs of the corresponding monocations are strictly ferrocenium in makeup. Predominant ethynyl character returns to the highest valence orbitals after loss of Li(+) from [1-Li](+) or loss of H(+) from [1-H](2+). These anodic processes hold promise for the controlled chemical modification of carbon and other electrode surfaces by a variety of ethynyl or alkynyl-linked organic and metal-containing systems.

Sequential “click” functionalization of mesoporous titania for energy-relay dye enhanced dye-sensitized solar cells

Energy relay dyes (ERDs) were immobilized in vicinity of energy-accepting injection dyes (IDs) via a sequential functionalization approach of mesoporous titania photo anodes in dye-sensitized solar cells.

Post-functionalization of graphitic carbon nitrides by grafting organic molecules: toward C–H bond oxidation using atmospheric oxygen

We present a feasible approach in the post-modification of carbon nitrides for the selective oxidation of 3,5,5-trimethylcyclohex-3-en-1-one.