Ana Martín-Lasanta

Ti(III)-catalyzed cyclizations of ketoepoxypolyprenes: control over the number of rings and unexpected stereoselectivities.

We describe a new strategy to control the number of cyclization steps in bioinspired radical (poly)cyclizations involving epoxypolyenes containing keto units positioned along the polyene chain. This approach provides an unprecedentedly straightforward access to natural terpenoids with pendant unsaturated side chains. Additionally, in the case of bi- and tricyclizations, decalins with cis stereochemistry have been obtained as a consequence of the presence of the ketone. The preferential formation of cis-fused adducts was rationalized using DFT calculations. This result is completely unprecedented in biomimetic cyclizations and permits the access to natural terpenoids with this stereochemistry, as well as to non-natural analogues.

Versatile Bottom-up Approach to Stapled π-Conjugated Helical Scaffolds: Synthesis and Chiroptical Properties of Cyclic o-Phenylene Ethynylene Oligomers†

Spring loaded: the smallest members of a family of carbon nanocoils (CNCs), adopting a fixed helical structure, have been synthesized by introduction of one or two staples in o-phenylene ethynylene oligomers. The chiroptical responses of the systems having enantiopure L-tartrate-derived staples confirmed the induced helicity. Theoretical studies suggest that these CNCs are pseudoelastic.

Toward Multiple Conductance Pathways with Heterocycle-Based Oligo(phenyleneethynylene) Derivatives

In this paper, we have systematically studied how the replacement of a benzene ring by a heterocyclic compound in oligo(phenyleneethynylene) (OPE) derivatives affects the conductance of a molecular wire using the scanning tunneling microscope-based break junction technique. We describe for the first time how OPE derivatives with a central pyrimidine ring can efficiently link to the gold electrode by two pathways presenting two different conductance G values. We have demonstrated that this effect is associated with the presence of two efficient conductive pathways of different length: the conventional end-to-end configuration, and another with one of the electrodes linked directly to the central ring. This represents one of the few examples in which two defined conductive states can be set up in a single molecule without the aid of an external stimulus. Moreover, we have observed that the conductance through the full length of the heterocycle-based OPEs is basically unaffected by the presence of the heterocycle. All these results and the simplicity of the proposed molecules push forward the development of compounds with multiple conductance pathways, which would be a breakthrough in the field of molecular electronics.

Development of a new dual polarity and viscosity probe based on the foldamer concept.

Small molecular probes able to act as sensors are of enormous interest thanks to their multiple applications. Here, we report on the development of a novel supramolecular dual viscosity and polarity probe based on the foldamer concept, which increases the resolution limits of traditional probes at low viscosity values (0-4 mPa·s). The applicability of this new probe has been tested with a supramolecular organogel.

Influence of the number of anchoring groups on the electronic and mechanical properties of benzene-, anthracene- and pentacene-based molecular devices.

One of the central issues of molecular electronics (ME) is the study of the molecule-metal electrode contacts, and their implications for the conductivity, charge-transport mechanism, and mechanical stability. In fact, stochastic on/off switching (blinking) reported in STM experiments is a major problem of single-molecule devices, and challenges the stability and reliability of these systems. Surprisingly, the ambiguous STM results all originate from devices that bind to the metallic electrode through a one-atom connection. In the present work, DFT is employed to study and compare the properties of a set of simple acenes that bind to metallic electrodes with an increasing number of connections, in order to determine whether the increasing numbers of anchoring groups have a direct repercussion on the stability of these systems. The conductivities of the three polycyclic aromatic hydrocarbons are calculated, as well as their transmission spectra and current profiles. The thermal and mechanical stability of these systems is studied by pulling and pushing the metal-molecule connection. The results show that molecules with more than one connection per electrode exhibit greater electrical efficiency and current stability.

Novel ortho-OPE metallofoldamers: binding-induced folding promoted by nucleating Ag(I)–alkyne interactions

We have developed a new family of ortho-oligophenylene ethynylene (o-OPE) metallofoldamers. The folding of these helicates is induced by nucleating carbon–metal interactions between Ag(I) cations and the alkynes of the inner core of the o-OPEs. These o-OPEs form metal–organic assemblies where at least three alkyne moieties are held in close proximity to form novel Ag(I)-complexes with the metal ion lodged into the helical cavity. NMR titration experiments and photokinetic studies have provided quantitative data about the thermodynamic and kinetic features of such binding/folding phenomena. X-ray diffraction and DFT studies have been performed to extract structural information on how the Ag(I) cation is accommodated into the cavity. The great simplicity and versatility of these new metallofoldamers open up the possibility to develop novel structures with applications in material science and/or in asymmetric catalysis.

Electronic properties of nanosize GNRs: The role of the anchoring groups

The electronic behavior of organic molecules, which could be considered as basic blocks of graphene nanoribbons, has been studied using Density Functional Theory and Non-Equilibrium Green Functions approaches. We have focused on the role that plays the molecule-metal contact, for this reason different configurations in the number and position of the contacts have been considered. We have noticed that the direct electron transport through the molecule is bigger than the diagonal one and the elimination of the π-cloud in the central benzene of the anthracene molecule involves important changes in the behavior of the whole device.