Diseño y síntesis de sistemas curcuminoides para aplicaciones en electrónica molecular

Tesis presentada a la Universidad de Chile para optar al grado académico de Doctor en QuímicaLa electrónica molecular es una rama de la nanotecnología cuya finalidad es la utilización de moléculas individuales como componentes electrónicos. Si consideramos que una molécula es la estructura estable más pequeña, alcanzar este grado de miniaturización sería el objetivo final en la búsqueda de dispositivos electrónicos más eficientes. Para esto, es necesario entender cómo las propiedades intrínsecas de una molécula afectan el desempeño de estos dispositivos, con el fin de desarrollar sistemas moleculares que posean propiedades interesantes y sean capaces de formar contactos robustos y confiables. El objetivo de esta tesis es el diseño y estudio de sistemas moleculares que puedan ser utilizados en la construcción de dispositivos basados en electrónica molecular. Considerando esto, los sistemas curcuminoides son posibles candidatos para electrónica molecular debido a que presentan una estructura altamente conjugada y versatilidad sintética que permite modificar químicamente su estructura, modulando así las propiedades observadas. En este sentido, se propusieron dos líneas de trabajo para esta tesis: 1) la modificación de los anillos aromáticos terminales con el fin de utilizarlos como grupos de anclaje; y, 2) la modificación del grupo -dicetona central con el fin de modular sus propiedades opto-electrónicas. Durante esta tesis se obtuvieron 11 ligandos orgánicos (ligandos curcuminoides 1-6; derivados heterocíclicos 1a, 2a, 4a y 4aa; y un ligando pseudo-curcuminoide 7), y 16 compuestos de coordinación (complejos con BF2 1b, 2b, 4b, 6b y 7b; y complejos con metales de transición I-IX), estudiándose sus propiedades opto-electrónicas mediante espectroscopia UV-Vis y electroquímica, para finalmente realizar estudios de conductancia molecular en un dispositivo MCBJ. A partir de los resultados obtenidos queda manifestada la relevancia de los grupos de anclaje al permitir el acoplamiento molécula-electrodo; por otro lado, las modificaciones al grupo -dicetona, mediante la formación de heterociclos o compuestos de coordinación, permite modular la conductancia molecular debido a los cambios producidos en la estructura electrónica. Se espera que los resultados obtenidos en esta tesis contribuyan a expandir el conocimiento sobre la relación existente entre la estructura electrónica de las moléculas y su conductancia molecular, y así en el futuro poder desarrollar dispositivos basados en electrónica molecular.Molecular electronics is a branch of nanotechnology which aims to use single molecules as electronic components. If we consider that a molecule is the smallest stable structure, achieving this degree of miniaturization is the ultimate goal in the search for more efficient electronic devices. To accomplish this is necessary to fully understand how the intrinsic properties of a molecule affect the performance of such devices, aiming to develop molecular systems with interesting properties and with the ability to form strong and reliable contacts. The purpose of this thesis is to design and study molecular systems which could be applied in the development of devices based on molecular electronics. Considering this, curcuminoid systems are candidates for molecular electronics because they exhibit a highly conjugated system and synthetic versatility allowing to chemically modify its structure, thereby modulating the properties of these systems. In this sense, two research lines were proposed: 1) the modification of the terminal aromatic rings to use them as anchoring groups; and, 2) the modification of the central -diketone moiety in order to modulate its opto-electronic properties. For this thesis 11 organic ligands (curcuminoid ligands 1-6; heterocyclic derivatives 1a, 2a, 4a and 4aa; and a pseudo-curcuminoid ligand 7), and 16 coordination compounds (BF2 complexes 1b, 2b, 4b, 6b and 7b; and transition metal complexes I-IX) were obtained, their opto-electronic properties were studied through UV-Vis spectroscopy and electrochemistry, to finally perform single-molecule conductance measurements in a MCBJ device. From the results obtained, the relevance of the anchoring groups is clear, allowing the molecule-electrode coupling; on the other hand, the modifications to the -diketone group, through the formation of heterocycles or coordination compounds, allows the modulation of the molecular conductance due to the changes produced in the electronic structure. It is expected that the results obtained in this thesis will contribute to expand the knowledge related with the dependance between the electronic structure of the molecules and their molecular conductance, and in the future development of devices based on molecular electronicsConicy

Multiscale approach to the study of the electronic properties of two thiophene curcuminoid molecules

et al.We studied the electronic and conductance properties of two thiophene–curcuminoid molecules, 2-thphCCM (1) and 3-thphCCM (2), in which the only structural difference is the position of the sulfur atoms in the thiophene terminal groups. We used electrochemical techniques as well as UV/Vis absorption studies to obtain the values of the HOMO–LUMO band gap energies, showing that molecule 1 has lower values than 2. Theoretical calculations show the same trend. Self-assembled monolayers (SAMs) of these molecules were studied by using electrochemistry, showing that the interaction with gold reduces drastically the HOMO–LUMO gap in both molecules to almost the same value. Single-molecule conductance measurements show that molecule 2 has two different conductance values, whereas molecule 1 exhibits only one. Based on theoretical calculations, we conclude that the lowest conductance value, similar in both molecules, corresponds to a van der Waals interaction between the thiophene ring and the electrodes. The one order of magnitude higher conductance value for molecule 2 corresponds to a coordinate (dative covalent) interaction between the sulfur atoms and the gold electrodes.This work has been funded by the FONDECYT REGULAR grants 1110206,1140770, and 1140199, PAI-CONICYT 79150041, Conicyt PFCHA 21140734, ANILLO project Act 1117, Millenium Project RC120001, the Dutch funding agencies FOM and NWO/OCW, by the EU through a RISE (DAFNEOX) project, SEP-210165479 by the MICINN of Spain (projects CTQ2012-32247 and MAT2013-47869- C4-2-P). N.A.-A. and R.D.-T. also acknowledge financial support from MINECO through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496).Peer Reviewe

Formation of self-assembled monolayer of curcuminoid molecules on gold surfaces

We investigated the formation of self-assembled monolayers of two thiophene curcuminoid molecules, 2-thphCCM (1) and 3-thphCCM (2), on polycrystalline gold substrates prepared by immersion of the surfaces in a solution of the molecules during 24 h. The functionalized surfaces were studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Despite the fact that both molecules have the same composition and almost the same structure, these molecules exhibit different behavior on the gold surface, which can be explained by the different positions of the sulfur atoms in the terminal aromatic rings. In the case of molecule 1, the complete formation of a SAM can be observed after 24 h of immersion. In the case of molecule 2, the transition from flat-lying to upright configuration on the surface is still in process after 24 h of immersion. This is attributed to the fact that molecule 2 have the sulfur atoms more exposed than molecule 1.Fil: Berlanga, Isadora. Universidad de Chile; ChileFil: Etcheverry Berríos, Álvaro. Universidad de Chile; ChileFil: Mella, Andy. Universidad de Chile; ChileFil: Jullian, Domingo. Universidad de Chile; ChileFil: Gómez Andrade, Victoria Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Chile; ChileFil: Aliaga-Alcalde, Núria. Institució Catalana de Recerca i Estudis Avancats; España. Universitat Autònoma de Barcelona; EspañaFil: Fuenzalida, Victor. Universidad de Chile; ChileFil: Flores, Marcos. Universidad de Chile; ChileFil: Soler, Monica. Universidad de Chile; Chil

Single-Molecule Transport of Fullerene-Based Curcuminoids

We present experimental and theoretical studies of single-molecule conductance through nonplanar fullerocurcuminoid molecular dyads in ambient conditions using the mechanically controllable break junction technique. We show that molecular dyads with bare fullerenes form configurations with conductance features related to different transport channels within the molecules, as identified with filtering and clustering methods. The primary channel corresponds to charge transport through the methylthio-terminated backbone. Additional low-conductance channels involve one backbone side and the fullerene. In fullerenes with four additional equatorial diethyl malonate groups attached to them, the latter transport pathway is blocked. Density functional theory calculations corroborate the experimental observations. In combination with nonequilibrium green functions, the conductance values of the fullerocurcuminoid backbones are found to be similar to those of a planar curcuminoid molecule without a fullerene attached. In the nonplanar fullerocurcuminoid systems, the highest-conductance peak occurs partly through space, compensating for the charge delocalization loss present in the curcuminoid system.Financial support from the European Commission (COST Action MOLSPIN CA15128 and EU RISE (DAFNEOX) project SEP-210165479) is gratefully acknowledged. The work at the University of Chile was supported by Fondecyt Regular Project 1181080 (D.D.), Fondecyt Regular Project 1161775 (M.S.), Fondecyt Regular Project 1170524 (D.A.), and Fondequip EQM140055 and EQM180009 (D.D). Powered@NLHPC: this research was partially supported by the supercomputing infrastructure of the NLHPC (ECM-02). E.R. acknowledges MICIIN for grant PGC2018-093863-B-C21 and the Maria de Maeztu Excellence grant MDM-2017-0767, for the computer resources, technical expertise, and assistance provided by the Barcelona Supercomputing Centre and CSUC and to the Generalitat de Catalunya for an ICREA Academia award and grant 2017SGR1289. H.S.J.v.d.Z. acknowledges support from the Dutch Science foundation (NWO). N.A.-A. thanks MEC for grant MAT2016-77852-C2-1-R, to the Generalitat de Catalunya for the grant 2017SGR1277, and the Severo Ochoa Program for Centers of Excellence in R&D (SEV-2015-0496). This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement 724981). L.E. thanks the US National Science Foundation (NSF) for generous support of this work under the CHE-1801317 program. The Robert A. Welch Foundation is also gratefully acknowledged for an endowed chair to L.E. (grant AH-0033).Peer reviewe

Electric-field induced bistability in single-molecule conductance measurements for boron coordinated curcuminoid compounds

© 2018 The Royal Society of Chemistry. We have studied the single-molecule conductance of a family of curcuminoid molecules (CCMs) using the mechanically controlled break junction (MCBJ) technique. The CCMs under study contain methylthio (MeS-) as anchoring groups: MeS-CCM (1), the free-ligand organic molecule, and two coordination compounds, MeS-CCM-BF2 (2) and MeS-CCM-Cu (3), where ligand 1 coordinates to a boron center (BF2 group) and to a CuII moiety, respectively. We found that the three molecules present stable molecular junctions allowing detailed statistical analysis of their electronic properties. Compound 3 shows a slight increase in the conductance with respect to free ligand 1, whereas incorporation of BF2 (compound 2) promotes the presence of two conductance states in the measurements. Additional experiments with control molecules point out that this bistability is related to the combination of MeS- anchoring groups and the BF2 moiety within the structure of the molecules