Joaquín Barberá

Herein, we present the development of tunable chiral nanoporous materials capable of enantioselectively adsorbing racemic mixtures. The materials are based on hydrogen-bonded supramolecular structures formed from a melamine derivative as the central core and three peripheral dendrons functionalized with coumarin and azobenzene moieties that are organized in hexagonal columnar phases. Upon irradiation with circularly polarized light (CPL), the azobenzene units induce controlled chirality in the material, which is stabilized by photodimerization of the coumarin moieties, obtaining mechanically stable films. The elimination of the melamine template results in nanoporous materials that retain their homeotropic hexagonal columnar alignment. These materials show selective adsorption of one particular enantiomer of racemic mixtures of (hexan-2-yl)-4-nitroaniline. Pore chirality can be reversed by changing the handedness of the CPL, allowing nanoporous materials to adsorb predominantly one or the other enantiomer. These findings offer a versatile strategy for enantioselective separation with potential applications in pharmaceuticals and materials science.

We present a new family of halogen-bonded pyridinium salts where both ionic partners participate in halogen bonding, leading to self-assembled smectic phases with nanosegregated ionic channels and high ionic conductivity.

We demonstrate that the liquid crystal behavior of subphthalocyanine bowl-shaped aromatics is governed by their chirality and the number and nature of peripheral substituents.

Herein, we report the first examples of supramolecular systems from bent-core-based pillar[n]arenes through ionic bonds. These ionic materials have been prepared by the interaction of an amino-ended pillar[5]arene (P5N10) and three different carboxylic acids, including bent-core moieties. The bent-core units are based on ester, biphenyl, and azobenzene structures bearing two different flexible spacers between the carboxyl group and the central bent-core aromatic units. The ionic pairs segregate the molecular blocks, leading to columnar liquid crystal organizations. These ionic supramolecular compounds exhibit interesting results as proton-conductive materials. Furthermore, the introduction of azobenzene units in the bent-core structure has provided a photoresponse to the proton conduction materials. Interestingly, the amphiphilic character generated by the ionic pairs and the hydrophobic bent-core structures allows their molecular self-assembly in water solution, resulting in aggregates of appealing morphologies. The structural modifications of the bent-core units (i.e., connecting bonds at the lateral structure and spacer lengths) provide an attractive analysis on the relationship between the chemical structure and the morphology of the aggregates (fibers, chiral ribbons, nanotubes...). Additionally, the self-assembly process and evolution of the aggregates from fibers to nanotubes have been studied with several techniques.

We present two hydantoin isomers that self-assemble through hydrogen bonding in solution and in bulk, either in a bowl-shaped or planar rosette, resulting in remarkable liquid crystals and gelation properties.

An easy and fast method to functionalize pillararenes through ionic bonds to obtain interesting materials for their encapsulation properties and proton conduction.

A series of six polybenzylic dendrons with an alkynyl focal point were synthesized for their incorporation to gold nanoparticles. Five of these compounds showed columnar mesomorphism in a wide range of temperatures. These dendrons were reacted with gold nanoparticles stabilized with a combination of a dodecanethiol and 11-azidoundecane-1-thiol. The azido group of the last compound allowed the functionalization of the nanoparticles with the six polybenzylic dendrons by 1,3-dipolar cycloaddition between their alkynyl groups and the terminal azido groups of the thiols. A high efficiency of the cycloaddition process (47–69%) was confirmed by several experimental techniques and no decomposition or aggregation phenomena were detected in the dendron-coated nanoparticles. The involved mechanism and the resulting percentage composition of the final materials are discussed. The results of the ulterior growth of the nanoparticles by thermal treatment are influenced by the size and the shape of the dendron and the temperature of the process. The structures of the final nanoparticles were investigated by TEM, DSC, TGA, NMR and UV-Vis spectroscopy. These nanoparticles do not show liquid crystal properties. However, a melting process between a crystalline and a fluid phase is observed. In the solid phase, the nanomaterials prepared show a short-range interaction between nanoparticles with a 2D local hexagonal order. A near-field effect was observed in the UV-vis spectra by coupling of different surface plasmon resonance bands (SPR) probably due to the short-range interactions. The main novelty of this work lies in the scarcity of previous studies of gold nanoparticles coated with dendrons forming themselves columnar mesophases. Most of the studies reported in the literature deal with gold nanoparticles coated with calamitic mesogens. Additionally, the effect of the thermal treatment, which in a previous paper was shown to increase the mean size of the nanoparticles without increasing their size polydispersity, has been studied in these materials.

Highly sensitive magnetometry reveals paramagnetism in dendrimer-coated gold nanoparticles. Different types of such nanoparticles, as a result of (i) functionalizing with two distinct Percec-type dendrons, linked to gold via dodecanethiol groups, and (ii) postsynthesis annealing in a solvent-free environment that further promotes their growth have been prepared. Ultimately, for each of the two functionalization configurations, we obtain highly monodisperse and stable nanoparticles of two different sizes, with spherical shape. These characteristics allow singling out the source of the measured paramagnetic signals as exclusively arising from the undercoordinated gold atoms on the surfaces of the nanoparticles. Bulk gold and the functional groups of the ligands contribute only diamagnetically.

Monodisperse dendrimer-coated gold nanoparticles with a spherical shape have been obtained by direct reduction of HAuCl₄ with sodium borohydride in the presence of dodecanethiol as a stabilizer and subsequent functionalization by ligand exchange reaction with polybenzylic thiolated dendrons. The substitution pattern of the dendrimeric units plays a fundamental role in the rate of the functionalization exchange process and consequently conditions the size and the polydispersity of the NPs obtained. An ulterior growth process occurs by thermal stimuli (150 °C) in a solvent-free environment. This method, carried out in mild conditions, allows the formation of highly monodisperse gold NPs with different sizes for different time reactions, and we discuss the mechanisms involved in this process. Finally, we demonstrate the chemical composition and stability of our compounds by structural, thermal, and chemical characterization of the samples before and after thermal treatment.