Imine-Based Architectures at Surfaces and Interfaces: From Self-Assembly to Dynamic Covalent Chemistry in 2D

Within the last two decades, dynamic covalent chemistry (DCC) has emerged as an efficient and versatile strategy for the design and synthesis of complex molecular systems in solution. While early examples of supramolecularly assisted covalent synthesis at surfaces relied strongly on kinetically controlled reactions for post-assembly covalent modification, the DCC method takes advantage of the reversible nature of bond formation and allows the generation of the new covalently bonded structures under thermodynamic control. These structurally complex architectures obtained by means of DCC protocols offer a wealth of solutions and opportunities in the generation of new complex materials that possess sophisticated properties. In this focus review we examine the formation of covalently bonded imine-based discrete nanostructures as well as one-dimensional (1D) polymers and two-dimensional (2D) covalent organic frameworks (COFs) physisorbed on solid substrates under various experimental conditions, for example, under ultra-high vacuum (UHV) or at the solid–liquid interface. Scanning tunneling microscopy (STM) was used to gain insight, with a sub-nanometer resolution, into the structure and properties of those complex nanopatterns

Photoisomerisation and light-induced morphological switching of a polyoxometalate–azobenzene hybrid

The functionalization of a spherical Keplerate-type polyoxometalate {Mo72V30} with a cationic azobenzene surfactant has been achieved through ionic self-assembly. The photoisomerisation reaction of this complex, which emerges in a light-triggered aggregation–disaggregation process, has been followed by 1H NMR spectroscopy, dynamic light scattering, absorption spectroscopy and scanning electron microscopy analyses

Synthesis and characterization of a new family of photoactive liquid crystalline polyesters based on a-methylstilbene

10.1002/pi.4507A liquid crystal polyester and two liquid crystal copolyesters containing a-methylstilbene moieties and aliphatic or aromatic spacers in the backbone were synthesized in good yields, with the aim of using them for photosensitive microcapsule preparation. The synthesized polymers were fully characterized with respect to thermal stability, type of mesophase, molecular weight and E¿Z photoisomerization. Combination of monomers with different structures allowed adjustment of the polymer characteristics such as degree of crystallinity and glass transition temperature, as verified using X-ray diffraction, polarized optical microscopy and differential scanning calorimetry. Quantitative 1H NMR and UV-visible experiments were performed in order to investigate E¿Z photoisomerization after photoirradiation at 364 nm. Finally, a membrane based on one of these polymers was prepared and it was found that its wettability increased on photoirradiation

Supramolecular complexes of cobalt(II), manganese(II) and cadmium(II) with bis(terpyridine) ligand as novel luminescent materials

Self-assembly of N6-donor bis(terpyridine) ligand L with transition metal ions: Co(II), Mn(II) and Cd(II) leads to a formation of three kinds of supramolecular complexes. In the electronic absorption and emission spectra of supramolecular complexes additional bands were observed what was ascribed to the coordination of ligand molecules to metal ions. Luminescence properties of these complexes strongly depend on the kind of metal ions and counter ions. The effective blue luminescence was observed in the case of Mn(II) and Cd(II) complexes in which all N-donor atoms of ligand molecules coordinate with the metal center

Graphene oxide-branched polyethylenimine foams for efficient removal of toxic cations from water

Highly porous foams based on graphene oxide functionalized with polyethylenimine are generated and used with unprecedented efficiency for adsorbing heavy metal ions. A multiscale analysis of the GO-BPEI nanocomposite provided evidence for the covalent grafting of BPEI on GO and the formation of low crystalline porous foams. The uptake experiments revealed that the GO-BPEI's adsorption of toxic cations is strongly dependent on the pH in range from 2 to 10, as a result of the different interactions at the supramolecular level between the metal ions and the GO-BPEI foam. The maximum uptake capacities for Cu(ii), Cd(ii) and Pb(ii) are achieved at pH = 5 and exhibit values as high as 1096, 2051 and 3390 mg g-1, respectively, being ca. over 20 times greater than standard sorbents like activated carbon. The GO-BPEI composite can be easily regenerated as proven by performing adsorption cycles. Also, the thermodynamic parameters including standard Gibbs free energy (ΔGo), the enthalpy change (ΔHo) and entropy change (ΔSo) revealed the exothermic and spontaneous nature of the adsorption process

Graphene oxide-mesoporous SiO2 hybrid composite for fast and efficient removal of organic cationic contaminants

In this study, we have developed a novel mesoporous SiO2 - graphene oxide hybrid material (SiO2NH2-GO) as highly efficient adsorbent for removal of cationic organic dyes from water. The fabrication of such a three-dimensional (3D) SiO2NH2-GO composite has been achieved via the condensation reaction between the amine units exposed on 3-aminopropyl-functionalized silica nanoparticles and the epoxy groups on surface of GO. As a proof-of-concept, SiO2NH2-GO was used for the removal of archetypical dyes from water and revealed outstanding maximum adsorption capacity towards methylene blue (MB), rhodamine B (RhB) and methyl violet (MV) at pH 10 reaching 300, 358 and 178 mg g−1 for MB, RhB and MV, respectively, thus outperforming the neat components of composite, i.e. GO and SiO2. Moreover, the adsorption process revealed that ∼99.7% of MB, RhB and MV have been removed in only 3 min thereby highlighting the superior nature of SiO2NH2-GO composite with respect to most of graphene oxide-based adsorbents of organic dyes. Finally, the composite was used in solid phase extraction (SPE) as column packing material, for continuous water purification, thus highlighting the great potential of SiO2NH2-GO for the large-scale removal of cationic dyes from aqueous solutions