Espaciadores Vinilénicos en Oligómeros Aromáticos: Espectroscopia Molecular en el Límite de la Alta Correlación pi-Electrónica

En la presente Tesis Doctoral se propone evaluar el impacto que diferentes perfiles de conjugación tienen sobre las propiedades electrónicas y estructurales de oligómeros basados en unidades repetitivas aromáticas y heteroaromáticas. En particular, se ha hecho hincapié en la combinación/implementación de espaciadores tipo vinilénico entre unidades aromáticas, explorando así nuevas estrategias para la optimización de la -conjugación molecular (reducción del gap HOMO — LUMO): (i) la variación de la planaridad / rigidez estructural y (ii) la funcionalización de las moléculas con unidades dadoras o aceptoras. Con este fin se ha desarrollado un protocolo de estudio basado en la realización, en primer lugar, de un análisis espectroscópico en detalle de las moléculas en estado neutro. Para establecer las principales relaciones estructura—propiedad se han combinado técnicas experimentales y modelización químico-cuántica básica. De forma complementaria, las especies cargadas de cada serie han sido evaluadas, prestando especial atención a la elucidación de la configuración electrónica de los sistemas objeto de estudio, para su clasificación como capa cerrada o capa abierta y, en este último caso, determinar la multiplicidad de espín del estado fundamental. Finalmente, se han estudiado los fenómenos de valencia mixta, de acuerdo a la teoría de Marcus, de los sistemas derivados de las series funcionalizadas con grupos electroactivos. De este modo, se ha puesto de manifiesto el efecto que tiene sobre dichos fenómenos la naturaleza del puente conjugado que conecta los centros redox

Methamphetamine removal from aquatic environments by magnetic microrobots with cyclodextrin chiral recognition elements

The growing consumption of drugs of abuse together with the inefficiency of the current wastewater treatment plants toward their presence has resulted in an emergent class of pollutants. Thus, the development of alternative approaches to remediate this environmental threat is urgently needed. Microrobots, combining autonomous motion with great tunability for the development of specific tasks, have turned into promising candidates to take on the challenge. Here, hybrid urchin-like hematite (α-Fe2O3) microparticles carrying magnetite (Fe3O4) nanoparticles and surface functionalization with organic β-cyclodextrin (CD) molecules are prepared with the aim of on-the-fly encapsulation of illicit drugs into the linked CD cavities of moving microrobots. The resulting mag-CD microrobots are tested against methamphetamine (MA), proving their ability for the removal of this psychoactive substance. A dramatically enhanced capture of MA from water with active magnetically powered microrobots when compared with static passive CD-modified particles is demonstrated. This work shows the advantages of enhanced mass transfer provided by the externally controlled magnetic navigation in microrobots that together with the versatility of their design is an efficient strategy to clean polluted waters.Web of Science202

Donor-acceptor polymers for applications in organic electronics and photovoltaics

We have synthesized a new series of high-mobility polymeric semiconductors with good processability and excellent environmental stability for organic electronics and photovoltaics. Using these materials, solar cells were fabricated with power conversion efficiencies of up to 8.7% and remarkable fill factors of 76-80%.MINECO, Junta de Andalucí

Organic Materials: The Effect of Subtle Modifications on Device Performance

In the search of new high-mobility polymeric semiconductors with good processability and excellent environmental stability, diverse synthetic strategies have been approached. One of the most widely used consists in the alternation of donor and acceptor moieties in the conjugated skeleton, which allows fine tuning of the polymer frontier molecular orbitals. For organic field effect transistors (OFETs) applications, low-lying HOMOs are essential to resist air oxidation and thus increase device stability. However, if the HOMO energy is too low, the resulting barrier to hole injection may compromise the transistor performance. Thus, a delicate balance between these two effects is needed. Furthermore, high performance solution-processable materials require the correct selection and positioning of the specific solubilizing substituents in order to achieve proper HOMO and LUMO energy levels, planar molecular conformations, close intermolecular π-π stacking, and proper thin film crystallinity. Following these two combined strategies, diverse polymeric materials with great performances in both OFETs and solar cells, and having remarkable air stability, have been synthesized and characterized. , This contribution will analyze how small modifications in their molecular structures can have a great impact on the device performance.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Oligo(3,4-etilendioxitiofeno-vineleno)s

Desde el descubrimiento de las propiedades conductoras del poliacetileno (PA)1 han sido muchas las modificaciones en la síntesis química que, manteniendo la estructura de enlaces conjugados, es decir, alternancia de dobles y sencillos, han buscado mejorar los niveles de movilidad o rendimientos cuánticos, modulación de absorciones y emisiones o estabilidad entre muchas cualidades. Probada la eficacia de incluir grupos vinileno entre anillos de tiofeno a nivel de -conjugación2, en esta comunicación presentamos la caracterización de una nueva serie oligómeros constituida por cadenas de tienileno-vinileno (nTV) de distinta longitud (dímero a tetrámero) con las posiciones beta de los tiofenos funcionalizadas con grupos etilendioxi (EDO) (Figura 1). El objetivo de este nuevo diseño químico es reforzar la estabilidad de la cadena conjugada de los nTV a través de las interacciones intramoleculares asociadas a los grupos EDO3, así como mejorar las propiedades de las especies oxidadas. De este modo, se detallarán las conclusiones más relevantes obtenidas de los estudios realizados de espectroscopia de absorción y emisión, para evaluar las propiedades del estado excitado, espectroscopia Raman con el fin de caracterizar la estructura molecular de esta nueva serie, así como voltametrías cíclicas y medidas de espectro- y espectroelectroquímica UV-VIS-NIR, que nos ayudaran a profundizar en la naturaleza de las especies oxidadas.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Allocation of Ambipolar Charges on an Organic Diradical with a Vinylene–Phenylenediyne Bridge

Two redox and magnetically active perchlorotriphenylmethyl (•PTM) radical units have been connected as end-capping groups to a bis(phenylene)diyne chain through vinylene linkers. Negative and positive charged species have been generated, and the influence of the bridge on their stabilization is discussed. Partial reduction of the electron-withdrawing •PTM radicals results in a class-II mixed-valence system with the negative charge located on the terminal PTM units, proving the efficiency of the conjugated chain for the electron transport between the two terminal sites. Counterintuitively, the oxidation process does not occur along the electron-rich bridge but on the vinylene units. The •PTM radicals play a key role in the stabilization of the cationic species, promoting the generation of quinoidal ring segments

Camouflaged Holes Assist Negative Charge Motion in Radical-Anion Molecular Wires

Charge transfer in molecular wires over varying distances is a subject of great interest in the field of molecular electronics. By increasing the distance between the electroactive centers, transport mechanisms generally accounted for on the basis of tunneling or superexchange operating over small distances, progressively gives way to hopping assisted transport. However, the underlying molecular sequential steps that likely take place during hopping and the operative mechanism occurring at intermediate distances have received much less attention given the difficulty in assessing detailed molecular-level information. We describe here the operating mechanisms for unimolecular electron transfer in the ground state of radical-anion mixed-valence derivatives occurring between their terminal perchlorotriphenylmethyl/ide groups through thiophene-vinylene oligomers that act as conjugated wires of increasing length up to 30 Å. In this sense, while in the shorter radical-anions a flickering resonance mechanism is the operative one, in the larger molecular wires, as a unique finding, the net transport of the electron is assisted by an electron-hole delocalization.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Interrogating the CISS effect in chiral and paramagnetic organic radicals : the impact of the molecular spin over the total spin polarization

Continuous research on new chiral molecular materials brings new exciting properties to the field of molecular electronics. The discovery of the chirality-induced spin selectivity (CISS) effect has expanded the list of applications for chiral structures, opening promising avenues for their exploitation in molecular spintronics. In this work, the persistent propeller-like organic perchlorotriphenylmethyl (PTM) radical is investigated as a potential spin filter combining chirality and paramagnetism. In particular, two different PTM derivatives, mono- and bis-functionalized, with one or two terminal alkyne groups have been used for the preparation of enantioenriched solid-state assemblies. The analysis of their chiroptical properties reveals that the functionalization does not play a crucial role in their final conformational stability and highlights the dissimilarities of the racemization barriers in solution and solid states. Spin-dependent electrochemical and charge transport measurements of enantioenriched PTM-based self-assembled monolayers did not reveal the existence of the CISS effect. Density functional theory quantum transport calculations show that the most dominant contribution to the spin polarization would not be CISS-related polarization, but the one intrinsically associated with the radical spin. Nevertheless, at room temperature this contribution is affected by thermal fluctuations averaging to a net zero spin polarization

Operative Mechanism of Hole-Assisted Negative Charge Motion in Ground States of Radical-Anion Molecular Wires

Charge transfer/transport in molecular wires over varying distances is a subject of great interest. The feasible transport mechanisms have been generally accounted for on the basis of tunneling or superexchange charge transfer operating over small distances which progressively gives way to hopping transport over larger distances. The underlying molecular sequential steps that likely take place during hopping and the operative mechanism occurring at inter mediate distances have received much less attention given the difficulty in assessing detailed molecular-level information. We describe here the operating mechanisms for unimolecular electron transfer/transport in the ground state of radical-anion mixed-valence derivatives occurring between their terminal perchlorotriphenylmethyl/ide groups through thiophene−vinylene oligomers that act as conjugated wires of increasing length up to 53 Å. The unique finding here is that the net transport of the electron in the larger molecular wires is initiated by an electron− hole dissociation intermediated by hole delocalization (conformationally assisted and thermally dependent) forming transient mobile polaronic states in the bridge that terminate by an electron−hole recombination at the other wire extreme. On the contrary, for the shorter radical-anions our results suggest that a flickering resonance mechanism which is intermediate between hopping and superexchange is the operative one. We support these mechanistic interpretations by applying the pertinent biased kinetic models of the charge/spin exchange rates determined by electron paramagnetic resonance and by molecular structural level information obtained from UV−vis and Raman spectroscopies and by quantum chemical modeling

Fingerprints of Through-Bond and Through-Space Exciton and Charge π-Electron Delocalization in Linearly Extended [2.2]Paracyclophanes

New stilbenoid and thiophenic compounds terminally functionalized with donor–donor, acceptor–acceptor, or donor–acceptor moieties and possessing a central [2.2]­paracyclophane unit have been prepared, and their properties interpreted in terms of through-bond and through space π-electron delocalization (i.e., π-conjugations). Based on photophysical data, their excited-state properties have been described with a focus on the participation of the central [2.2]­paracyclophane in competition with through-bond conjugation in the side arms. To this end, two-photon and one-photon absorption and emission spectroscopy, as a function of temperature, solvent polarity, and pressure in the solid state have been recorded. Furthermore, charge delocalization through the [2.2]­paracyclophane in the neutral state and in the oxidized species (radical cations, dications and radical trications) has been investigated, allowing the elucidation of the vibrational Raman fingerprint of through-space charge delocalization. Thus, a complementary approach to both “intermolecular” excitation and charge delocalizations in [2.2]­paracyclophane molecules is shown which can serve as models of charge and exciton migration in organic semiconductors