–––––The department has been involved in the last years in several projects, financed by different public research agencies and private corporations, which are related with Multifunctional Molecular Materials, Molecular Nanoscience, and Molecule-Based Nanotechnology. In most of these projects the “bottom-up approach” has been extensively used since this approach takes advantage of Supramolecular Chemistry that permits to organize molecules in the solid state as well as molecular nano-objects on surfaces obtaining respectively bulk crystalline materials and nanostructurated surfaces with nanoscopic entities showing pre-designed physical –conductivity, magnetism, and optical - and chemical properties.

Multifunctional Molecular Materials. In this field we are involved in the design and preparation of the following kind of materials:

1.        Magnetic molecular materials. Our main objective has been to understand and optimize magnetic interactions between the unpaired electrons of open-shell organic molecules –free organic radicals- to create purely organic and metal-organic magnets. Special attention was paid to those materials combining magnetism with chirality being remarkable the preparation of one of the rare examples of enantiopure molecular magnets that shows a spin avalanche phenomenon.

2.        Electrically conducting molecular materials. We have developed synthetic routes that allow the preparation of different multisulfur p-donors, derived from tetrathiofulvalene (TTF). With these donors several new crystalline charge transfer complexes and salts have been prepared. Remarkable are the metallic conductivity observed for different TTF-derived compounds as well as the charge transfer salts showing magnetic properties along with metallic conductivities. One very new and interesting result is the multistability in a BEDT-TTF based molecular organic conductor that is able to be tuned between three different polymorphs with distinct magnetic and electrical properties by external stimuli.

Polymorphic transformations of the salt (BEDT-TTF)₂Br_1.3I_1.1Cl_0.6

3.        Nonlinear optical magnetic molecular materials. In this direction we have obtained for the first time purely organic open-shell molecules showing significant nonlinear optical activities that approach to the highest limit reported up to date. The octupolar nature of some of the optically active free radicals is also very interesting, since they are one of the scarce molecular species showing this special characteristic.

Molecular Nanoscience. In this field most of our objectives deal with Molecular Electronics both in Sensu Stricto -i.e. electronics at the molecule scale- and Sensu Lato; -i.e., electronics based on molecules. In particular we are working in the following research areas:

1.        Synthesis and characterization of new nanostructurated electrically conductive thin-films. These new kind of nanocomposite polymeric materials show relevant mechanical, electrical and optical properties that permit to use them as sensors and circuits. Thus, such nanocomposite polymers are transparent and flexible showing conductivities that can be modified from superconductors to semiconductors by changing the components. Moreover, such thin films have one conducting surface while the other one is dielectric and can be patterned by a heath source expanding the possible applications.

Metallic film formed by the (BET-TTF)₂Br·₃ H₂O salt and a resistance drawn by a laser on the conducting surface of the film.

 2.        Preparation and study of new single-molecule magnets, such as Mn12 complexes, of hybrid nature as nanoscopic devices for information magnetic storage devices with very high densities and also for quantum computation (qubits) purposes. Interesting are also the results we have already obtained addressed to obtain nano-patterned surfaces with these single-molecule magnets and that are showed in the figure.

AFM image of a nanopatterned surface of biphenyl Mn₁₂ single molecule magnet  fabricated on a large area of a substrate of native silicon oxide deposited onto Si(100)

3.        Synthesis and study of new molecular organic wires for electronic transport to be used as nanoscopic electronic components. We are studying the electron transfer phenomenon within these molecular nano-objects that ranges from 1 to 4 nm trying to understand the different molecular parameters that influence such a phenomenon.

4.        Preparation and manipulation of optically active chiral bidimensional surfaces, composed of metallic surfaces and organic molecules, with potential application in catalysis. Thus, we have been investigating supramolecular organizations obtained by the self-assembling of molecules on different surfaces and how the chiral information of the molecules is transmitted to such supramolecular organizations. Particularly interesting is the analogy existing in the resulting 3-D (crystals) and 2-D (surfaces) supramolecular organizations.

A high-resolution STM image of a racemic formamide (9.6 x 9.6 nm2, 1.0 nA, -0.58 V) at the 1-heptanol/graphite interface

5.      Bidimensional surfaces patterned with different electroactive molecules as TTF have also been prepared and studied being able to modify the patterning with the modification of the TTF derivative. Interestingly scanning tunneling spectroscopy at the individual molecule level reveals rectifying behaviour, independent of the molecular ordering.

6.        Synthesis preparation and study of organic field effect transistors is being pursued and very interesting results had been obtained with the preparation of organic field effect transistors (OFETs) based on single crystals of tetrathiafulvalene derivatives, which show the highest charge carrier mobility found for an organic device prepared from solution. This result is very important since the combination of high performance and solution processability makes these materials very promising for technological applications. The maximum mobility observed in these crystals has been as high as 3.5 cm²/Vs with an ON/OFF > 10⁶. In addition , the comparison of the device performances using crystals of very similar molecules but with different crystal packing allowed for the focused investigation of the influence of the intermolecular interactions on the electronic transport properties. OFETs based on a family of TTFs were studied and a clear correlation between the crystal structure and the electrical characteristics was observed

7.        Development of new bistable molecular devices with nanoscopic sizes -molecular switches- having electronic, optic and/or magnetic functionalities. In this field we have been working with bi- (or multi-) stable molecules showing valence tautomerism phenomena in which the different states of the molecules show different magnetic and optical properties. The discovery of a completely new type of compounds showing valence tautomers was remarkable.     

                                     Multiproperty multistate electrochemical switch based on a Ferrocene substituted radical

 8.        Synthesis and study of new molecular nanoporous materials with magnetic properties that show new physico-chemical phenomena –confined reactions, multifunctional properties, magnetic sensors, etc. For this research activity we have been using different open-shell molecules as metal ligands for obtaining metal-organic open-frameworks that present nanoporous and magnetic properties. Remarkable is the preparation of a molecular magnetic sponge that might be used as sensor in the future.

View of the crystal packing of MOROF-1 showing the channels formed by the hexagonal pores with dimensions 3.1 x 2.8 nm

Molecule-based Nanotechnology. In this area, one of the most relevant contributions developed at the NMMO, in collaboration with several industrial partners, has been the development of a new method for the preparation of nanocrystalline powders of molecular compounds. This method, named DELOS^®, permits to control the particle size and size distribution and uses compressed fluids (CO₂) as an alternative solvent to the organic ones. This new crystallization procedure has several ecological benefits and has been patented in several countries. Until now we have applied this new method for industrial crystallizations in the pharmaceutical and polymeric sectors obtaining drugs with new performances and characteristics and also for the obtaining of very small crystals of single molecule magnets.

Mn12 single molecule magnet microcrystals processed by DELOS®