High-performance vitrimers from commodity thermoplastics through dioxaborolane metathesis.

Windmills, cars, and dental restoration demand polymer materials and composites that are easy to process, assemble, and recycle while exhibiting outstanding mechanical, thermal, and chemical resistance. Vitrimers, which are polymer networks able to shuffle chemical bonds through exchange reactions, could address these demands if they were prepared from existing plastics and processed with fast production rates and current equipment. We report the metathesis of dioxaborolanes, which is rapid and thermally robust, and use it to prepare vitrimers from polymers as different as poly(methyl methacrylate), polystyrene, and high-density polyethylene that, although permanently cross-linked, can be processed multiple times by means of extrusion or injection molding. They show superior chemical resistance and dimensional stability and can be efficiently assembled. The strategy is applicable to polymers with backbones made of carbon-carbon single bonds.

Directing the Self-Assembly Behaviour of Porphyrin-Based Supramolecular Systems.

The self-assembly behaviour of a library of tetra-amidated porphyrin molecules decorated with a variety of solubilizing wedges is investigated as dilute solutions in methylcyclohexane. Small changes in the solubilising wedge of the porphyrins resulted in different aggregated states, as evidenced by CD and UV/Vis absorption spectroscopy. The porphyrins form co-facially stacked H-aggregates, slip-stacked J-aggregates or a mixture of both. Detailed thermodynamic and kinetic analysis showed that in all cases the formation of J-aggregates proceeds via an isodesmic mechanism whereas H-aggregates are formed via a cooperative mechanism. It is shown that these aggregates assemble in a parallel pathway, in which both compete for the monomer, compared to a sequential pathway, in which one of the aggregates interconverts into the other. Interestingly, kinetic analysis of porphyrins that only form H-aggregates in thermodynamic equilibrium revealed that the competing pathway towards J-aggregates is operational in these systems as well. Our findings show that the balance between H- and J-aggregates depends on remarkably small changes in the architecture of the solubilising wedges.

Efficient routes to A3B-type meso-(4-carboxyphenyl) porphyrin derivatives.

A3B-type meso-(4-carboxyphenyl) porphyrins were prepared either by stepwise coupling of aniline substituents to meso-tetrakis(4-carboxyphenyl) porphyrin (TCPP) or by utilizing its partially protected trimethyl ester derivative. We demonstrate the high utility of this building block, which can be synthesized in very good yields by microwave-assisted Me3SnOH hydrolysis.

Small sized perylene-bisimide assemblies controlled by both cooperative and anti-cooperative assembly processes.

Cooperative aggregation of monomers into one-dimensional nanostructures typically results in elongated objects. Here we analyse in depth the self-assembly of an N-monoarylated perylene bisimide which shows characteristics of a cooperative growth mechanism but unexpectedly yields objects of small size, due to anti-cooperativity by attenuated growth.

Stealth rare earth oxide nanodiscs for magnetic resonance imaging.

Configuring RE(2) O(3) nanocrystals with pseudo-2D morphologies confers substantive gains in relaxivities over equivalent spherical counterparts. The most promising arises from Gd(2) O(3) whose ionic transverse and longitudinal relaxivities were as high as r(1) = 12.7 mM(-1) s(-1) and r(2) = 17.2 mM(-1) s(-1) (dispersed in H(2) O, T = 37 °C & B(0) = 1.41 T), pointing to new opportunities to achieve high contrast MRI while concomitantly affording longer half-life potential in vivo.

Plasmonic chiroptical response of silver nanoparticles interacting with chiral supramolecular assemblies.

Silver nanoparticles were prepared in aqueous solutions of chiral supramolecular structures made of chiral molecular building blocks. While these chiral molecules display negligible circular dichroism (CD) as isolated molecules, their stacking produced a significant CD response at room temperature, which could be eliminated by heating to 80 °C due to disordering of the stacks. The chiral stack-plasmon coupling has induced CD at the surface plasmon resonance absorption band of the silver nanoparticles. Switching between two plasmonic CD induction mechanisms was observed: (1) Small Ag nanoparticles coated with large molecular stacks, where the induced plasmonic CD decayed together with the UV molecular CD bands on heating the solution, indicating some type of electromagnetic or dipole coupling mechanism. (2) Larger Ag nanoparticles coated with about a monolayer of molecules exhibited induced plasmonic CD that was temperature-independent. In this case it is estimated that the low chiroptical response of a molecular monolayer is incapable of inducing such a large chiroptical effect, and a model calculation shows that the plasmonic CD response may be the result of a slight chiral shape distortion of the silver nanoparticles.

Processable cyclic peptide nanotubes with tunable interiors.

A facile route to generate cyclic peptide nanotubes with tunable interiors is presented. By incorporating 3-amino-2-methylbenzoic acid in the D,L-alternating primary sequence of a cyclic peptide, a functional group can be presented in the interior of the nanotubes without compromising the formation of high aspect ratio nanotubes. The new design of such a cyclic peptide also enables one to modulate the nanotube growth process to be compatible with the polymer processing window without compromising the formation of high aspect ratio nanotubes, thus opening a viable approach toward molecularly defined porous membranes.

Multicolour self-assembled fluorene co-oligomers: from molecules to the solid state via white-light-emitting organogels.

Five fluorene-based co-oligomers have been prepared to study their self-assembly in a wide range of concentrations, from dilute solutions to the solid state. Subtle changes to the chemical structures, introduced to tune the emission colours over the entire visible range, induce strong differences in aggregation behaviour. Only two of the fluorescent co-oligomer derivatives self-assemble to form soluble fibrils from which fluorescent organogels emerge at higher concentrations. In contrast, the other compounds form precipitates. Mixed fluorescent co-oligomer systems exhibit partial energy transfer, which allows the creation of white-light-emitting gels. Finally, a mechanism for the hierarchical self-assembly of this class of materials is proposed based on experimental results and molecular modelling calculations.

Multicolour self-assembled particles of fluorene-based bolaamphiphiles.

Bolaamphiphilic fluorene-based oligomers self-assemble in water to form fluorescent nanoparticles with tuneable emission colours covering the entire visible range, even including white.