Adamantane-type clusters: compounds with a ubiquitous architecture but a wide variety of compositions and unexpected materials properties

The research into adamantane-type compounds has gained momentum in recent years, yielding remarkable new applications for this class of materials. In particular, organic adamantane derivatives (AdR4) or inorganic adamantane-type compounds of the general formula [(RT)4E6] (R: organic substituent; T: group 14 atom C, Si, Ge, Sn; E: chalcogenide atom S, Se, Te, or CH2) were shown to exhibit strong nonlinear optical (NLO) properties, either second-harmonic generation (SHG) or an unprecedented type of highly-directed white-light generation (WLG) - depending on their respective crystalline or amorphous nature. The (missing) crystallinity, as well as the maximum wavelengths of the optical transitions, are controlled by the clusters' elemental composition and by the nature of the organic groups R. Very recently, it has been additionally shown that cluster cores with increased inhomogeneity, like the one in compounds [RSi{CH2Sn(E)R'}3], not only affect the chemical properties, such as increased robustness and reversible melting behaviour, but that such 'cluster glasses' form a conceptually new basis for their use in light conversion devices. These findings are likely only the tip of the iceberg, as beside elemental combinations including group 14 and group 16 elements, many more adamantane-type clusters (on the one hand) and related architectures representing extensions of adamantane-type clusters (on the other hand) are known, but have not yet been addressed in terms of their opto-electronic properties. In this review, we therefore present a survey of all known classes of adanmantane-type compounds and their respective synthetic access as well as their optical properties, if reported.

Synthesis of substituted triazole-pyrazole hybrids using triazenylpyrazole precursors

A synthesis route to access triazole-pyrazole hybrids via triazenylpyrazoles was developed. Contrary to existing methods, this route allows the facile N-functionalization of the pyrazole before the attachment of the triazole unit via a copper-catalyzed azide-alkyne cycloaddition. The developed methodology was used to synthesize a library of over fifty new multi-substituted pyrazole-triazole hybrids. We also demonstrate a one-pot strategy that renders the isolation of potentially hazardous azides obsolete. In addition, the compatibility of the method with solid-phase synthesis is shown exemplarily.

Symmetry-breaking dynamics in a tautomeric 3D covalent organic framework

The enolimine-ketoenamine tautomerism has been utilised to construct 2D covalent organic frameworks (COFs) with a higher level of chemical robustness and superior photoelectronic activity. However, it remains challenging to fully control the tautomeric states and correlate their tautomeric structure-photoelectronic properties due to the mobile equilibrium of proton transfer between two other atoms. We show that symmetry-asymmetry tautomerisation from diiminol to iminol/cis-ketoenamine can be stabilised and switched in a crystalline, porous, and dynamic 3D COF (dynaCOF-301) through concerted structural transformation and host-guest interactions upon removal and adaptive inclusion of various guest molecules. Specifically, the tautomeric dynaCOF-301 is constructed by linking the hydroquinone with a tetrahedral building block through imine linkages to form 7-fold interwoven diamondoid networks with 1D channels. Reversible framework deformation and ordering-disordering transition are determined from solvated to activated and hydrated phases, accompanied by solvatochromic and hydrochromic effects useful for rapid, steady, and visual naked-eye chemosensing.

Transition-Metal-Free Synthesis of Polyfluoro-Polyarylmethanes via Direct Cross-Coupling of Polyfluoroarenes and Benzyl Chlorides

The transition-metal-free direct cross-coupling between polyfluoroarenes and benzyl chlorides is reported. In this strategy, a variety of polyfluoro di-, tri- and tetra-arylmethanes was efficiently prepared with good to excellent yields in the presence of Mg turnings via a one-pot procedure. Significantly, this method provides a general approach for the synthesis of polyfluorinated polyarylmethanes.

Synthesis of Electron-Rich Porous Organic Polymers via Schiff-Base Chemistry for Efficient Iodine Capture

As one of the main nuclear wastes generated in the process of nuclear fission, radioactive iodine has attracted worldwide attention due to its harm to public safety and environmental pollution. Therefore, it is of crucial importance to develop materials that can rapidly and efficiently capture radioactive iodine. Herein, we report the construction of three electron-rich porous organic polymers (POPs), denoted as POP-E, POP-T and POP-P via Schiff base polycondensations reactions between Td-symmetric adamantane knot and four-branched “linkage” molecules. We demonstrated that all the three POPs showed high iodine adsorption capability, among which the adsorption capacity of POP-T for iodine vapor reached up to 3.94 g·g⁻¹ and the removal rate of iodine in n-hexane solution was up to 99%. The efficient iodine capture mechanism of the POP-T was investigated through systematic comparison of Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) before and after iodine adsorption. The unique π-π conjugated system between imine bonds linked aromatic rings with iodine result in charge-transfer complexes, which explains the exceptional iodine capture capacity. Additionally, the introduction of heteroatoms into the framework would also enhance the iodine adsorption capability of POPs. Good retention behavior and recycling capacity were also observed for the POPs.

Gating Effects for Ion Transport in Three-Dimensional Functionalized Covalent Organic Frameworks

The development of bioinspired nano/subnano-sized (<2 nm) ion channels is still considered a great challenge due to the difficulty in precisely controlling pore's internal structure and chemistry. Herein, for the first time, we report that three-dimensional functionalized covalent organic frameworks (COFs) can act as an effective nanofluidic platform for intelligent modulation of the ion transport. By strategic attachment of 12-crown-4 groups to the monomers as ion-driver door locks, we demonstrate that gating effects of functionalized COFs can be activated by lithium ions. The obtained materials exhibit an outstanding selective ion transmission performance with a high gating ratio (up to 23.6 for JUC-590), which is among the highest values in metal ion-activated solid-state nanochannels reported so far. Furthermore, JUC-590 offers high tunability, selectivity, and recyclability of ion transport proved by the experimental and simulated studies.

Towards hydrogen and halogen bonded frameworks based on 3,5-bis(triazolyl)pyridinium motifs

Construction of supramolecular assemblies using hydrogen and halogen bonding between anions and the 3,5-bis(triazolyl)pyridinium motif was investigated.

Direct radical functionalization methods to access substituted adamantanes and diamondoids

Adamantane derivatives have diverse applications in the fields of medicinal chemistry, catalyst development and nanomaterials, owing to their unique structural, biological and stimulus-responsive properties, among others. The synthesis of substituted adamantanes and substituted higher diamondoids is frequently achieved via carbocation or radical intermediates that have unique stability and reactivity when compared to simple hydrocarbon derivatives. In this review, we discuss the wide range of radical-based functionalization reactions that directly convert diamondoid C-H bonds to C-C bonds, providing a variety of products incorporating diverse functional groups (alkenes, alkynes, arenes, carbonyl groups, etc.). Recent advances in the area of selective C-H functionalization are highlighted with an emphasis on the H-atom abstracting species and their ability to activate the particularly strong C-H bonds that are characteristic of these caged hydrocarbons, providing insights that can be applied to the C-H functionalization of other substrate classes.

Design of solvatomorphic structures based on a polyboronated tetraphenyladamantane molecular tecton

A series of solvatomorphic structures of tetrakis(4-dihydroxyborylphenyl)adamantane were investigated.

Diamondoid architectures from halogen-bonded halides

Halide ions and tetraiodoethynyl-featured tetraphenylmethane are successfully assembled into robust diamond-like networks in the presence of tetraphenylphosphonium cations.

Fast and efficient synthesis of microporous polymer nanomembranes via light-induced click reaction

Conjugated microporous polymers (CMPs) are materials of low density and high intrinsic porosity. This is due to the use of rigid building blocks consisting only of lightweight elements. These materials are usually stable up to temperatures of 400 °C and are chemically inert, since the networks are highly crosslinked via strong covalent bonds, making them ideal candidates for demanding applications in hostile environments. However, the high stability and chemical inertness pose problems in the processing of the CMP materials and their integration in functional devices. Especially the application of these materials for membrane separation has been limited due to their insoluble nature when synthesized as bulk material. To make full use of the beneficial properties of CMPs for membrane applications, their synthesis and functionalization on surfaces become increasingly important. In this respect, we recently introduced the solid liquid interfacial layer-by-layer (LbL) synthesis of CMP-nanomembranes via Cu catalyzed azide–alkyne cycloaddition (CuAAC). However, this process featured very long reaction times and limited scalability. Herein we present the synthesis of surface grown CMP thin films and nanomembranes via light induced thiol–yne click reaction. Using this reaction, we could greatly enhance the CMP nanomembrane synthesis and further broaden the variability of the LbL approach.

Palladium-catalysed synthesis of triaryl(heteroaryl)methanes

Tetraarylmethane derivatives are desirable for a variety of applications, but difficult to access with modern C-C bond-forming reactions. Here we report a straightforward method for palladium-catalysed arylation of aryl(heteroaryl)methanes and diaryl(heteroaryl)methanes with aryl chlorides. This reaction enables introduction of various aryl groups to construct triaryl(heteroaryl)methanes via a C-H functionalization in good to excellent yield, and represents the first step towards a general transition metal catalysed synthesis of tetraarylmethanes.

Radical exchange reaction of multi-spin isoindoline nitroxides followed by EPR spectroscopy

The synthesis and exchange reaction of a rigid, isoindoline-functionalized tetraphenylmethane multi-spin system is described. The exchange reaction was followed using EPR spectroscopy.

Polycationic adamantane-based dendrons form nanorods in complex with plasmid DNA

Different HYDRAmers are synthesized and complexed to a model plasmid DNA. Appropriate chemical modifications can improve efficiently the complexation to get HYDRAplexes, in form of long nanorods, with very good DNA binding and protecting properties.

Layer-by-layer Synthesis and Transfer of Freestanding Conjugated Microporous Polymer Nanomembranes

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in combination with their outstanding thermal and chemical stability, and low densities. However, their insoluble nature causes problems in their processing since usually applied techniques such as spin coating are not available. Especially for membrane applications, where the processing of CMP as thin films is desirable, the processing problems have hindered their commercial application. Here we describe the interfacial synthesis of CMP thin films on functionalized substrates via molecular layer-by-layer (l-b-l) synthesis. This process allows the preparation of films with desired thickness and composition and even desired composition gradients. The use of sacrificial supports allows the preparation of freestanding membranes by dissolution of the support after the synthesis. To handle such ultra-thin freestanding membranes the protection with sacrificial coatings showed great promise, to avoid rupture of the nanomembranes. To transfer the nanomembranes to the desired substrate, the coated membranes are upfloated at the air-liquid interface and then transferred via dip coating.

Self-assembly. Selective assemblies of giant tetrahedra via precisely controlled positional interactions

Self-assembly of rigid building blocks with explicit shape and symmetry is substantially influenced by the geometric factors and remains largely unexplored. We report the selective assembly behaviors of a class of precisely defined, nanosized giant tetrahedra constructed by placing different polyhedral oligomeric silsesquioxane (POSS) molecular nanoparticles at the vertices of a rigid tetrahedral framework. Designed symmetry breaking of these giant tetrahedra introduces precise positional interactions and results in diverse selectively assembled, highly ordered supramolecular lattices including a Frank-Kasper A15 phase, which resembles the essential structural features of certain metal alloys but at a larger length scale. These results demonstrate the power of persistent molecular geometry with balanced enthalpy and entropy in creating thermodynamically stable supramolecular lattices with properties distinct from those of other self-assembling soft materials.

Self-assembly of a tetrapodal adamantane with carbazole branches into hollow spherical aggregates in organic media

A hydrophobic tetrapodal molecule is composed of carbazole units at the periphery linked by a phenyl spacer on an adamantane core. Tetrapodal adamantane self-assembles into hollow spherical aggregates with a multilayer membrane in organic media. The spherical assembly size is dependent on the organic solvent used. Hollow spheres can entrap guest molecules within their internal spaces. By increasing the concentrations of tetrapodal molecules, hollow spheres fused into necklace-shaped nanostructures and two-dimensional networks were obtained.

DNA-porphyrin hybrids as reaction centers for photosensitized ene reactions with singlet oxygen

Recent developments in DNA-mediated nanostructuring have paved the way for the development of novel reaction centers. As part of a project focused on nanostructured reaction centers for reactions catalyzed by porphyrins, we have developed a solid-phase synthesis of tetrakis(p-hydroxyphenyl)porphyrin-oligonucleotide hybrids. In these hybrids, up to four nucleic acid chains are linked to the phenolic substituents of the porphyrin via phosphodiester linkages. A representative hybrid with one oligonucleotide chain of the sequence TTAA was found to survive light irradiation under aerobic conditions for 2 h with less than 35% oxidation of the DNA chain. An assay measuring the diastereo- and enantioselectivity of the photosensitized ene reaction of mesitylol with singlet oxygen was set up that provides diastereomeric ratios via NMR of aliquots of the reaction solution. Enantiomers were separated gas chromatographically on a chiral stationary phase and were assigned based on the product distribution obtained with an enantiomerically enriched starting material. Our results are a starting point for the exploration of nanostructured reaction media based on DNA and porphyrins.

Solution-phase synthesis of branched DNA hybrids via H-phosphonate dimers

A method for the solution-phase synthesis of branched oligonucleotides with tetrahedral or pseudo-octahedral geometry is described that involves the coupling of 3'-H-phosphonates of protected dinucleoside phosphates and organic core molecules. The dimer building blocks are produced by a synthesis that requires no chromatographic purification and that produces the dimer H-phosphonates in up to 44% yield in less than three days of laboratory work. A total of seven different branched hybrids were prepared, including a new hybrid of the sequence (CG)(4)TBA, where TBA stands for tetrakis(p-hydroxybiphenyl)adamantane that assembles into a material from micromolar aqueous solution upon addition of MgCl(2).

An adamantane-based building block for DNA networks

DNA governs the storage and transfer of genetic information through generations in all living systems with the exception of some viruses. Its physicochemical nature and the Watson-Crick base pairing properties allow molecular constructions at nanometer length, thereby enabling the design of desired structural motifs, which can self-assemble to form large supramolecular arrays and scaffolds. The tailor-made DNAs have been an interesting material for such designed nanoscale constructions. However, the synthesis of specific structures with a desired molecular function is still in its infancy and therefore has to be further explored. To add a new dimension to this approach, we have synthesized a rigid three-way branched adamantane motif, which is capable of forming highly stable DNA networks. The moiety generated could serve as a useful building block for DNA-based nanoconstructions.