Aryl Diazonium Compounds Research Articles

Electrochemical Functionalization of Selectively Addressed MoS2 Nanoribbons for Sensor Device Fabrication

Tailoring the surface properties of 2D materials, such as transition metal dichalcogenides (TMDCs), at the nanoscale is becoming essential in the fabrication of various 2D material-based nanoelectronic devices. Due to the chemical inertness of their basal plane, the surface modification of 2D TMDCs is limited to their defective sites, often requiring special treatments, such as the conversion of the TMDC from its semiconducting into its metallic phase. In this work, we show that the basal plane of a semiconducting 2D TMDC, molybdenum disulfide (MoS2) can be modified electrochemically by electrografting of aryl-diazonium salt. To demonstrate the advantages of this method at the nanoscale, we perform electrografting of 3,5-bis(trifluoromethyl)benzenediazonium tetrafluoroborate on predefined MoS2 nanoribbons by addressing them individually via a different electrode. The ability to selectively address individually contacted 2D layers opens the possibility for specific surface modification of neighboring 2D nanostructures by different functional groups. This method could be extended to other aryl-diazonium compounds, and other 2D semiconducting materials.

Intrinsic Tunneling Characteristics of Aryl Alkane Monolayers Sandwiched Between Single-Layer Graphene Electrodes

In this study, we report on charge transport through aryl alkane monolayers sandwiched between single-layer graphene (SLG) electrodes. Raman spectroscopy identified the chemically grafting of aryl diazonium compounds onto bottom SLG electrodes. Current densities of three different aryl alkane monolayers were exponentially deceased with a correct decay coefficient (β) as the length of a tunneling barrier increased. Transition voltage measurements for variable lengths of alkyl chains showed that the SLG/monolayer/SLG arrangement provides the formation of a valid tunneling junction to observe intrinsic charge transport properties of the incorporated molecules. This study demonstrated the possible application of the SLG electrodes to the test beds of molecular junctions.

Grafting nanocorrals onto graphite

Nanomaterials The electrochemical reduction of a mixture of two aryl diazonium compounds on graphite can lead to the formation of an array of nanoscale corrals. Phan et al. found that reduction of 4-nitrobenzenediazonium or 3,5-bis- tert -butylbenzenediazonium (TBD) alone creates aromatic radicals that graft homogeneously to the graphite surface. However, mixtures of these compounds created a quasi-periodic array of open regions that ranged from 45 to 130 nanometers. Mixtures richer in the more sterically hindered TBD resulted in larger diameters. The authors suggest that open corrals form from nanobubble structures created by N2 released in the reduction process that prevent access of the reactants to the graphite surface. ACS Nano 10.1021/acsnano.9b00439 (2019).

Graphite and Graphene Fairy Circles: A Bottom-Up Approach for the Formation of Nanocorrals.

A convenient covalent functionalization approach and nanopatterning method of graphite and graphene is developed. In contrast to expectations, electrochemically activated dediazotization of a mixture of two aryl diazonium compounds in aqueous media leads to a spatially inhomogeneous functionalization of graphitic surfaces, creating covalently modified surfaces with quasi-uniform spaced islands of pristine graphite or graphene, coined nanocorrals. Cyclic voltammetry and chronoamperometry approaches are compared. The average diameter (45-130 nm) and surface density (20-125 corrals/μm2) of these nanocorrals are tunable. These chemically modified nanostructured graphitic (CMNG) surfaces are characterized by atomic force microscopy, scanning tunneling microscopy, Raman spectroscopy and microscopy, and X-ray photoelectron spectroscopy. Mechanisms leading to the formation of these CMNG surfaces are discussed. The potential of these surfaces to investigate supramolecular self-assembly and on-surface reactions under nanoconfinement conditions is demonstrated.

Wohl‐Ziegler Bromination of Electrografted Films for Optimizing Atom Transfer Radical Polymerization

AbstractElectrografting of aryldiazonium compounds to conducting surfaces is extensively used to alter the surface properties. The highly reactive aryl radical is the actual grafting reagent, which on one hand is pertinent for the efficiency of the procedure but, on the other hand, in some cases is problematic by introducing unwanted side reactions. The electrografting of e.g. 4‐(bromomethyl)benzenediazonium is often carried out with the aim of creating a film that may serve as initiator for a controlled atom transfer radical polymerization. Unfortunately, this is difficult to accomplish because of bromine abstraction reactions occurring during the grafting process, which diminish the bromine content of the grafted layer significantly. Yet, this problem may be resolved by enriching the initiator film with bromine through a Wohl‐Ziegler bromination prior to the polymerization. An alternative pathway consisting of grafting 4‐methylbenzenediazonium followed by a bromination reaction to introduce bromine atoms at the benzylic position is shown to work equally well. Additionally, bromination of grafted benzyl alcohol groups have been explored. Finally, the repaired bromine films are used as a platform for atom transfer radical polymerization.

Blocking Properties of Nickel Electrodes Modified with Aryldiazonium Compounds

Blocking Properties of Nickel Electrodes Modified with Aryldiazonium Compounds

An improved method for functionalisation of carbon nanotube spun yarns with aryldiazonium compounds

We report a method for modifying carbon nanotube (CNT) spun yarns with aryldiazonium salts that involves the pH controlled application of the diazonium salts to CNTs both during and after the yarn formation process. This largely facilitates the chemical accessibility to CNTs within the yarn, potentially enabling a more extensive and uniform modification. The modified CNT yarns were characterised by X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy, and also examined for their mechanical properties. The results demonstrated that a CNT spun yarn was effectively modified by this method without impairing the yarn integrity. The formation of oligomerised polyene structures on the CNT surfaces was observed. This modification resulted in an increase in tensile strength and Young’s modulus of the CNT yarn. The functional groups grafted on CNTs also provide opportunities to form crosslinks in the yarn to further improve mechanical properties.

On the interfacial chemistry of aryl diazonium compounds in polymer science

AbstractThis review emphasises the role of aryl diazonium compounds as a new class of coupling agents for grafting polymer thin layers onto carbon, diamond, metals, metal oxides, alloys, semi-conductors, ceramics, and polymers. Physical and chemical methods are first reported for anchoring aryl layers to the surfaces, then the review concentrates on the modification of the above substrates by thin polymer films via a range of the “grafting from” and “grafting onto” strategies. Some applications are described which highlight the important role that diazonium salts will continue to play in the near future in the polymer and surface sciences.

A Comparative Study of the Modification of Gold and Glassy Carbon Surfaces with Mixed Layers of In Situ Generated Aryl Diazonium Compounds

AbstractIn situ generated aryl diazonium cations were synthesized in the electrochemical cell by reaction of the corresponding amines with NaNO2 in aqueous HCl. This paper reports a study of the formation of mixed layers from in situ generated aryl diazonium cations. Firstly, glassy carbon (GC) and gold electrode surfaces were modified with five single in situ generated aryl diazonium salts to obtain their corresponding reductive potential followed by the modification of GC and gold surfaces with eight binary mixed layers of in situ generated aryl diazonium salts. The difference between GC and gold surfaces in terms of in situ formation of two‐component aryl diazonium salt films was compared. The behavior of the mixed layers formed from in situ generated aryl diazonium salts relative to diazonium salts that were pre‐synthesized prior to surface modification was also investigated. Cyclic voltammetry and X‐ray photoelectron spectroscopy were used to characterize the resulting modified GC and gold surfaces. It is found that for some aryl diazonium salts the potential at which reductive adsorption is achieved on gold and GC surfaces is significantly different. For the eight sets of binary mixed layers, the species with more anodic potential are more difficult to attach to the both GC and gold surfaces. The behavior of the mixed layers formed from in situ generated aryl diazonium salts and the pre‐synthesized diazonium salts is similar; which emphasizes the advantage of the in situ approach without any apparent difference in behavior to the presynthesized diazonium salts.

The synthesis of 5-amino-4-arylazo-3-methyl-1 H-pyrazoles and 5-aryl-3-methylpyrazole[3,4-e][1,2,3,4]tetrazines

AlCl 3-catalyzed coupling of 3-amino-5-methyl-1 H-pyrazole in water with different aryldiazonium compounds yielded 5-amino-4-arylazo-3-methyl-1 H-pyrazole derivatives in high yield; subsequent diazotization and cyclization realised the 5-aryl-3-methylpyrazole[3,4-e][1,2,3,4]tetrazine derivatives. The structure of these novel, hetarylazo dyes was confirmed by UV–vis, FT-IR, and 1H NMR spectroscopic techniques and elemental analysis. Optimal preparation conditions for 5-amino-4-phenylazo-3-methyl-1 H-pyrazole were determined with respect to the effects of the AlCl 3-catalyst, pH and temperature; the reaction mechanism of formation of the 5-aryl-3-methylpyrazole[3,4-e][1,2,3,4]tetrazines is discussed and the colours of the aminopyrazoles and pyrazolo-tetrazine dyes in a range of solvents are also discussed.

Self-assembly of functionalized single-walled carbon nanotubes prepared from aryl diazonium compounds on Ag surfaces

Self-assembly of the sidewall functionalized single-walled carbon nanotubes (SWNTs) has been performed on Ag surfaces. The covalently functionalized SWNTs with benzoic acid moieties are prepared via diazonium reactions from 4-aminobenzoic acid and isoamyl nitrite. Raman, infrared, thermal gravimetric analysis (TGA) data, and solubility increase of SWNTs have indicated the modification of the sidewall of SWNTs. The functionalized SWNTs appeared to be assembled on Ag surfaces through the carboxylate group as evidenced from the emerging ν s(COO −) peak at ∼ 1380 cm − 1 .

Indirect Reduction of Aryldiazonium Salts onto Cathodically Activated Platinum Surfaces: Formation of Metal−Organic Structures

Platinum phases of general formula [Pt(n-), M+, MX] can be electrogenerated from cathodic polarization in dry dimethylformamide containing a supporting electrolyte, MX. The reaction of these electrogenerated Pt phases as reducing agent with aryldiazonium salts was investigated for preparing controlled metal-organic interfaces and characterizing the reactivity of the "reduced platinum phases". In a two-step process, the "reduced platinum phase" locally reacts with aryldiazonium salts, leading to the attachment of aryl groups onto the metal surface in the previously modified areas. Detailed experiments using cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and in situ electrochemical atomic force microscopy (EC-AFM) were carried out to follow the reaction in solution with the example of NaI as supporting electrolyte (MX = NaI). These studies demonstrate the irreversible attachment of aryl groups onto the platinum electrode. Comparison between the direct electroreduction of aryldiazonium compounds (4-nitrophenyl- and 4-bromophenyldiazonium) on a platinum electrode and their reaction with [Pt2-, Na+, NaI] suggests that a similar general mechanism is responsible for the grafting. However in the second case, no applied potential is required to stimulate the binding thanks to the reductive properties of [Pt2-, Na+, NaI]. Competitive reduction of the organic layer and growth of the layer were observed and analyzed as a function of the injected charge used to initially produce [Pt2-, Na+, NaI]. Similar reactions are highly probable with other MX salts owing to the redox properties observed for this type of platinum phase ([Pt(n-), M+, MX]).

Preparative Fluorous Mixture Synthesis of Diazonium-Functionalized Oligo(phenylene vinylene)s

[structure: see text] A series of building blocks for the synthesis of oligo(phenylene vinylene)s (OPVs) and hybrid oligomers were prepared, and alternating Heck coupling and Horner-Wadswoth-Emmons (HWE) reactions were used to couple the building blocks. Model studies were carried out to optimize the reaction strategies. The products were made to bear aryl diazonium functionalities that allow them to be used as surface grafting moieties in hybrid silicon/molecule assemblies. A library of OPV and hybrid oligomer tetramers was synthesized using fluorous mixture synthesis (FMS). The fluorous tags, which are secondary amines bearing different numbers of fluorine atoms, were synthesized and used as phase tags in mixture synthesis. The tags and substrates were anchored together by triazene linkages. The mixture synthesis was monitored by analytical HPLC on a fluorous column, and isolation of final OPV and hybrid oligomer tetramers was achieved by preparative HPLC. At the end of the FMS, after demixing, the tagged products were detagged by cleaving the triazene linkage and generating a series of aryl diazonium compounds. The fluorous tags could be recovered and reused. The NMR spectra of the 1-aryl-3,3-dialkyltriazenes are discussed.

Highly Functionalized Carbon Nanotubes Using in Situ Generated Diazonium Compounds

The thermal reaction of single-wall carbon nanotubes with in situ generated aryl diazonium compounds is described and is compared to a previously reported, electrochemically induced reaction with preformed aryl diazonium salts.

Photochemically induced breakdown of rod-like micelles: light-induced viscosity changes

The photochemical decomposition of three types of azo compound is used to change the viscosities of surfactant solutions. The azo additives are solubilized in systems containing rod-like cetyl-pyridinium salicylate micelles, and decomposed by UV irradiation. For solubilized 4-hexyl-phenyl-diazonium chloride, the viscosity reduces to 14% of its initial value after photolysis. Aryl-diazonium compounds suffer from thermal instability. Sodium 3-alkyl-phenyl-azosulphonates, which are more stable in the solid phase and in aqueous solution, exhibit a strong tendency to decompose on contact with the micellar solution. In contrast, the compound 3-methyl-phenyl-azo-phenylsulphone is stable in the micelles. On UV irradiation the viscosity reduces to 6% of its value after solubilization. The concentration of azo additive required to produce the photorheological effect corresponds to one-seventh of the surfactant concentration. A quantum yield of 0.025 ± 0.002 has been determined for the photolysis at 308 nm in toluene and ethanol. On average, approximately 11 quanta per solubilized molecule are required to produce the viscosity breakdown. Gas chromatography—mass spectrometry (GC—MS) analysis reveals that alkyl-benzenes are the products of the photochemical reaction in the micellar system: these hydrocarbons decrease the viscosity, as they convert the rod-like micelles into small spherical aggregates.

Photolytic inhibition and labeling of proteins with aryl diazonium compounds.

In the course of preparing aryl azide derivatives for use as photoprobes, we have observed significant light sensitivity in the precursor aryl diazonium compounds. The photosensitive properties of this class of compounds are of interest since they will seek out cationic binding sites in biological targets, and can be employed to inhibit complementary targets at acid pH. The relationship between photolytic change in the structure of diazonium compounds and the corresponding change in function of a biological target are presented. Experiments are described in which the dark and light sensitive properties of a model diazonium compound, diazobenzene sulfonate (DBS), were determined. The ultraviolet spectra were used to evaluate the dark stability and light sensitivity of DBS. Chymotrypsin and trypsin served as functioning targets for further evaluation of the photochemical properties. Both enzymes are stable to the probe in the dark at acid pH. A rapid loss of enzyme activity was observed following flash photolysis of DBS-enzyme solutions. Photolytic incorporation of radioactive DBS into chymotrypsin was observed. Aryl diazonium salts can be employed to probe the availability of complementary sites in biological targets at different acid pH values.

Reduction of aryldiazonium compounds in nonpolar media

Reduction of aryldiazonium compounds in nonpolar media

Crown-cation complex effects. IV. Crown ether and quaternary ion mediated displacements in aryldiazonium compounds

Crown-cation complex effects. IV. Crown ether and quaternary ion mediated displacements in aryldiazonium compounds

Chemistry of sulfonylmethyl isocyanides. 11. Synthesis of 1,2,4-triazoles from tosylmethyl isocyanide and aryldiazonium compounds

Chemistry of sulfonylmethyl isocyanides. 11. Synthesis of 1,2,4-triazoles from tosylmethyl isocyanide and aryldiazonium compounds

3 The Medicinal Chemistry of 1,2,3-Triazines

Publisher Summary This chapter focuses on the medicinal chemistry of 1,2,3-benzotriazines (2), benzotriazines (3) fused at the c bond to an azino- or azolo-ring (x), and the important series of hetero-fused 1,2,3-triazines (4). Some of the chemical and biological properties of diazonium compounds have been summarized in the chapter. The close parallel between the chemical properties of aryldiazonium compounds and 1,2,3-triazines fused to an aromatic carbocyclic or heterocyclic ring has been repeatedly stressed in this chapter. A medicinally desirable diazonium compound would test the skills of the most talented pharmaceutical formulator because of the inherent instability of this structural type: fused 1,2,3-triazines on the other hand are, in general, stable crystalline compounds readily amenable to manipulation yet lacking little in chemical versatility. Only a small proportion of the many structurally diverse 1,2,3-triazines that have been prepared over the years have been examined for biological activity.