Synthesis, Characterization and Deposition on Surfaces of Curcuminoids-based Systems

Abstract

Nanoscience and Nanotechnology have become research areas that promote the design and fabrication of novel devices with a number of different applications with the aim of satisfying the growing demand of the society regarding technological advances. The breakthrough in some of these subjects directly associates with the development of specific molecular systems with new and advanced features, applicable toward the development, at the nanoscale, of efficient materials that could act as molecular switches or active components in memory devices, transistors or sensors, among others. In this regard, promising molecular-based systems, to be applicable in these fields, are the so-called Curcuminoids (CCMoids). These molecules can present versatile structures, displaying always (i) a conjugated chain of seven carbon atoms, which confers the molecules with reasonable conductive properties; (ii) a β-diketone group located in the middle of the chain, that opens the possibility of coordinating with metallic centers, and (iii) two aromatic groups, located on both sides of the molecules that add fluorescent, redox active and optical properties, among others. The main goal of this thesis rest on the design and synthesis of new CCMoids that can be applied in different areas of nanoscience. Thus, different modifications on their structure were carried out in order to achieve interesting properties. The results obtained in this work have been grouped in five different sections; corresponding each one to a different area. This way:

(1) Molecular Magnetism: the first section is focused on the search of systems which display interesting magnetic properties, especially systems with single molecule magnet behavior. Thus, magneto-structural studies were performed by the synthesis of several coordination compounds using magnetic metallic centers (CoII and NiII) coordinate with a CCMoid ligand called 9Accm. In addition, a study of the influence of the paramagnetic centers on the fluorescent properties derived from the CCMoid ligand was also performed together with deposition studies on HOPG (highly oriented pyrolytic graphite).

(2) Molecular Electronic: the second section focuses on the study of the electronic transport of a new CCMoid system within a three terminal nanodevice containing few layer graphene (FLG) electrodes. This study centers in the improvement of the conductive properties of a previously measured CCMoid system, in which 9Accm was used as a nanowire in a molecular transistor by π-π stacking interactions with the graphene electrodes. The new CCMoid

contains an elongated conjugated skeleton that improves the anchoring properties of the final system with the FLG electrodes.

(3) Molecular Sensors: the third section is based on the immobilization of fluorescent CCMoids on surfaces and their used as chemical sensors for boron ions. The immobilization was carried out on functionalized SiO2 surfaces by the use of the Microcontact printing technique (μ-CP) that allowed the creation of fluorescent micropatterns on the surfaces. In addition, studies regarding the coordination of boron to the CCMoids attached on the surfaces and the effect in their fluorescent properties was performed to explore they as chemical sensors.

(4) Molecular Host-Guest Chemistry: the fourth section is focused on the fabrication of supramolecular host-guest systems based on CCMoids. In the first part, a study of the CCMoid acting as a guest was performed. In this case, a novel CCMoid molecule that contain a ferrocene group is inserted in different host cavities (cyclodextrin and cucurbituril). This study was performed in solution and on Au surfaces. On the other hand, the synthesis of another CCMoid was carried out to be used as a host, being the main ligand in the formation of molecular cages.

(5) Molecular Donor/Acceptor Chemistry: the fifth section is based on the study of the donor/acceptor properties of additional CCMoids with the idea of using them as components of organic photovoltaics cells (OPVs). For this study, the synthesis of two families of CCMoids with acceptor and donor moieties on the sides of the molecules was performed, and additional variations on their structure were achieved to assess their influence on the optical and electronic properties of the systems.

La nanociencia y la nanotecnología se han erigido como las áreas encargadas en diseñar y fabricar nuevos dispositivos cada vez más potentes y rápidos con el fin de satisfacer la creciente demanda tecnológica de nuestra sociedad. Una familia de moléculas muy prometedoras para ser aplicable en estos campos es la conocida como Curcuminoides (CCMoides) debido a su gran versatilidad. Esta tesis se centra en el diseño y síntesis de nuevos CCMoides para su posterior aplicación en diferentes campos de la nanociencia. Para ello, se han llevado a cabo distintas modificaciones en sus estructuras con el fin de conseguir propiedades interesantes. Los resultados obtenidos han sido agrupados en 5 secciones, cada uno de los cuales corresponde a un área de investigación diferente: (1) Magnetismo Molecular: La primera sección se centra en la búsqueda de sistemas que presenten propiedades de imán molecular. Para ello, se llevó a cabo un estudio magneto- estructural mediante la síntesis de varios compuestos de coordinación utilizando centros metálicos magnéticos (CoII y NiII) coordinados con el ligando CCMoide llamado 9Accm.

(2) Electrónica Molecular: La segunda sección se centra en el estudio del transporte electrónico de un nuevo sistema CCMoide como parte activa de un sistema de tres terminales que actúa como transistor molecular de efecto campo.

(3) Sensor Molecular: La tercera sección se centra en la inmovilización de CCMoides fluorescentes en superficies funcionalizadas que puedan actuar como sensores químicos de boro. Esta inmovilización se llevara a cabo en superficies de SiO2 mediante el uso de la técnica Microcontact printing.

(4) Huésped-Anfitrión Molecular: La cuarta sección se centra en la fabricación de sistemas supramoleculares huésped-anfitrión. El primer estudio se centra en la utilización de ligandos CCMoide (huésped), que interaccionan con dos sistemas (ciclodextrina y cucurbiturilo) (anfitriones). Por otro lado, se realizó la síntesis de un nuevo CCMoide con el objetivo de que pudiese actuar como anfitrión mediante la formación de cajas moleculares.

(5) Dador-Aceptor Molecular: La quinta sección se centra en el estudio de las propiedades aceptoras/dadoras de CCMoides para que puedan ser utilizados en la fabricación de celdas fotovoltaicas orgánicas (OPVs), llevándose a cabo la síntesis de dos familias de CCMoides con grupos aceptores y dadores.