Understanding Cross-Conjugation for Organic Electronics

Comunicación a congresopi-Conjugated organic molecules have been the focus of interest since they have been probed as potential semiconducting materials,[1] suitable for replacing the widely used silicon technologies. Their structural, optical and conductive properties are now under study to improve their application in organic electronics and to make possible their ad hoc synthesis. In this sense, the knowledge of the pi-electron delocalization is crucial to stablish the relation between the properties and the function, enabling the development of a synthesis guide based on the specific application. The most acknowledged conjugated organic materials are those which present extended, linearlyconjugated pi-systems. [1,2] However, this is not the only way of pi-electron delocalization: homoconjugation, cross-conjugation, curved-conjugation, etc. constitute different electronic designs to achieve new organic materials. There is a relative high abundance in the organic world of cross-conjugated but limited comprehension. [1,2,3] Thus, the understanding of how cross-conjugation works in -electronic systems is of importance. Following this idea, in this project we show 4 different structures which present two perpendicular pi-conjugated paths and how the cross-conjugated property is revealed. On the one hand, two molecules based on thieno[3,4-c]pyrrole-4,6-dione quaterthiophenes[2,3] allow us toaccomplish the subject from the aromatic/quinoidal outlook, and, on the other hand, two molecules with an anthanthrone core make possible the study from the perspective of the substituent groups. [4]Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Cholesteric aggregation at the quinoidal-to-diradical border enabled stable n-doped conductor

Resumen de la comunicaciónSemiconductor materials constitute the heart of solar cells since they are responsible of the photovoltaic effect. For this reason, the search of new materials to improve the efficiency and stability of these devices is on the focus of the organic electronics. These semiconductors are typically formed by p-doped materials. Despite the relative high abundance of molecules suitable for photovoltaic purposes, that is, able of absorbing light and allowing the transport of the new created charges through them, n-doped organic semiconductors are not plentiful due to their well-known ambient instability.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Polyconjugation from molecular spectroscopy

Abstract de la comunicación oralThe discovery of the semiconducting properties of π-conjugated organic oligomers and polymers has been a turning point in the development of new electronic devices and transformed the study of these systems in an emerging research field. Since then, many efforts have been devoted to generate structural features that bring about new and outstanding properties for optoelectronics, spintronics and magnetic devices, nonlinear optics, or singlet fission processes. Since the behavior of the π-electrons determines the properties of these molecules, establishing not only the electron delocalization mechanism and its extension, but also which factors disturb the πelectron density is of utmost importance to enhance the proper performance of these materials and develop ad hoc synthesis for desired application. In this context, the coexistence of alternative π-electron delocalization frameworks with the main linearly conjugated sequence must be considered as the existence of contributing resonance structures can modify significantly the optical, electronic and molecular properties of the system under study. In this communication, three different policonjugation patterns are addressed and their influence on the π-systems is revealed through electronic and vibrational spectroscopies. Through-bond π-electron delocalization is exemplified by molecules with cross-conjugated and parallelly-conjugated frameworks. For the former, the two πconjugated pathways compete for the π-electron density in the common sections of the molecule. Conversely, parallel π-conjugated sequences do not share any fragment. On the other hand, through-space π-conjugation is demonstrated in spiro molecules, in which a proper spatial configuration allows the interaction between π-conjugated moieties disconnected by an insulating atom.RSEQ Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Diradicals shaped by double pi-conjugation: contribution from molecular spectroscopy.

En general, se ha encontrado que la deslocalización de los electrones π en las moléculas más pequeñas tiene lugar en los anillos de benceno, mientras que para los oligómeros de mayor longitud, debido a la configuración capa abierto de su estado electrónico fundamental, dicha deslocalización se produce preferentemente a través de los bordes tipo “silla” de la molécula. Esta deslocalización da lugar a un comportamiento tipo poliacetilénico para los oligorilenos que presentan un elevado carácter dirradical. La secuencia de π-conjugación lineal a través los bordes tipo “silla” establece la conexión entre los dos centros radicalarios que explica la configuración singlete del estado fundamental de estos sistemas, es decir, permite la activación del mecanismo de doble polarización de espín. El estudio de estas familias permite el establecimiento de una serie de pautas generales acerca del comportamiento de los electrones π en un sistema dirradical linealmente conjugado, de forma que en los capítulos siguientes se evaluará su alteración con la presencia de secuencias π-conjugadas alternativas.La presente tesis doctoral está enfocada al estudio de las estructuras electrónica y molecular de sistemas orgánicos que presentan varias secuencias de conjugación de los electrones π, así como de sus propiedades ópticas y electrónicas y su uso potencial en dispositivos electrónicos orgánicos. Para conseguir este propósito, las estructuras electrónicas y moleculares de siete sistemas diferentes han sido caracterizadas mediante espectroscopía de absorción electrónica UV-Vis-NIR y espectroscopías vibracionales Raman e IR. En todos los casos, los resultados obtenidos se han apoyado en cálculos químico-cuánticos, además de emplearse técnicas alternativas cuando ha sido posible (como resonancia paramagnética electrónica, conductancia de moléculas individuales o absorción de estados excitados). La investigación de estos sistemas orgánicos se ha realizado atendiendo a los diferentes modos de conjugación de los electrones π que presentan. El estudio de cada uno de estos modos ha sido abordado desde estructuras iniciales aromáticas y quinoides capaces de experimentar una transformación hacia sistemas de capa abierta, es decir, dirradicales. En la Sección A se ha realizado la caracterización de dos series de ciclopentaoligorrilenos linealmente monoconjugados, una de ellas de carácter aromático (CP-nR) y la segunda, quinoide (nR-2N). El hecho de que ambas familias presenten una transformación de capa cerrada a capa abierta en estado neutro al aumentar el tamaño del oligómero ha permitido realizar una descripción completa del comportamiento de la densidad de electrones π en una secuencia de conjugación lineal, tanto de carácter aromático como quinoide

Polyconjugation for Organic Electronics

Since the discovery of the semiconducting properties of π-conjugated organic oligomers and polymers, many efforts have been devoted to generating structural features that bring about new and outstanding properties for optoelectronics, spintronics and magnetic devices, non-linear optics, or singlet fission processes. In this sense, the play between the resonance and π-electron delocalization phenomena in π-conjugated organic materials is the origin of their semiconducting behavior. For this reason, establishing not only the electron delocalization mechanism and its extension, but also which factors disturb the π-electron density is of utmost importance to enhance the proper performance of the electronic devices and develop ad hoc synthesis for desired application.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Raman spectroscopy as a versatile tool to study organic biradicals

Since -conjugated organic molecules were probed as potential semiconducting materials, suitable for replacing the widely used silicon technologies, their structural, optical and conductive properties have been under study to improve their application in organic electronics and to make possible their ad hoc synthesis. In this sense, the modification of the -electron delocalization path is one of the available tools to tune the properties of the molecules to obtain the desired characteristics for the fabrication of these devices. One of the parameters employed to tailor -conjugated organic molecules for organic electronics is the diradical character. A progressive change in the diradical contribution to the ground electronic state structure can tune some of the main system features, highlighting the HOMO-LUMO energy gap and the aggregation mode. The main drawback of this approach is the loss of chemical stability when increasing the diradical character of these molecules. On the other hand, the -electron delocalization can be interrupted introducing a perpendicularly conjugated path. The competition of these two cross-conjugated patterns leads to a new 2-dimensional delocalization scenario that changes the electronic properties of the studied materials. In this project, we present a stable quinoidal quaterthiophene diradical that possess outstanding stability and conductivity properties. [1] The combination of the diradical character together with the possibility to delocalize the electron density through two different perpendicular paths explain its exceptional behavior in comparison with the other members of the series, or with its linearly conjugated analogues. The balance between these two properties has been evaluated through UV-Vis-NIR electronic spectroscopy and Raman and IR vibrational spectroscopy in the neutral and charged forms of the target molecule and similar non-cross-conjugated samples.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

SEQUENTIAL INDUCTION OF CHIRALITY IN POLY(PHENYLACETYLENE)S

Several hierarchical levels of chirality have been detected in functionalized poly(phenylacetylene)s (PPA).1 In this work we have studied the chirality induction throughout these levels in PPA functionalized with phenylglycine methyl ester groups, Fig. 1.2 These pendant groups force the PPA chain to lose its planar all-transoid shape to form helical structures. The chiral seed of the pendants, [(R)- or (S)-], dictates the preferent handedness of the helices, both the internal polyacetylene helical covalent backbone and the external helix formed by the side pendants which forms a complementary helix or counter-helix. In this work, we afford a full assessment of the interconnection between stereocenter and helix sources of chirality and the action of these polymers as chiral templates of other supra-molecular structures with inherited chiral properties. We then used VCD spectroscoy to demonstrate the chiral induction from the stereogenic centers to the backbone helix and from this to the pendant helix, which are largely promoted by two mechanisms: steric effects and hydrogen bonding. In addition, the VCD spectra supported that the helical setup of the pendants induces the solvent DMSO molecules to adopt a solvation helix around the polymer, thus proving how an achiral solvent becomes chirally organized owing to the template effect of the covalent polymer helices. A similar effect was observed in DMSO solutions of the monomeric units. Interestingly, this resulted in opposite helical sense to the one observed in the polymer with identical enantiomeric form.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Characterization of size-sorted particulated matter collected on solid substrates by laser-ionization mass spectrometry and laser-induced breakdown spectrometry

Resumen de trabajos realizados mediante excitación láser de material particulado y su posterior análisis mediante espectroscopía óptica de emisión o ionización.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Sequential Induction of Chirality in Helical Polymers: From the Stereocenter to the Achiral Solvent

This is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of the Physical Chemistry Letters, Copyright © 2018 American Chemical Society after peer review and technical edityng by the publisher. To access the final edited and published work see: https://pubs.acs.org/doi/10.1021/acs.jpclett.8b00519Several steps of chiral induction have been detected in poly(phenylacetylene)s among their different hierarchical levels of chirality by vibrational circular dichroism, namely, (i) from the stereogenic centers to the innermost polyacetylene helical covalent backbone (helixint), (ii) from this to the external helix (helixext) formed by the side phenyl pendants that form a complementary helix or counter-helix, and (iii) from this pendant helix to the helical solvation sphere (helixsolv.), the last one being observed along this work. The pendant to polyene backbone chiral induction determines the helical structure adopted by the polymer and therefore the solvation helix. This helical structure is promoted by two mechanisms: steric effects and hydrogen bonding. An important finding concerns the demonstration by VCD of how an achiral solvent becomes chirally organized owing to the template effect of the covalent polymer helices, an effect that is silent to other structural techniques such as ECD or AFM and that hence significantly broadens the scope of these previous analysesFinancial support from Ministerio de Ciencia e Innovación [CTQ2014-61470-EXP, CTQ2015- 69391-P, FPI (R. Rodríguez), FPU (S. Medina), Juan de la Cierva postdoctoral Fellowship FJCI- 2015-23531 (B.Nieto-Ortega)], Xunta de Galicia (GRC2014/040, Centro singular de investigación de Galicia accreditation 2016-2019, ED431G/09) and the European Regional Development Fund (ERDF) is gratefully acknowledgedS

Direct Magnetic Evidence, Functionalization, and Low-Temperature Magneto-Electron Transport in Liquid-Phase Exfoliated FePS3

Magnetism and the existence of magnetic order in a material is determined by its dimensionality. In this regard, the recent emergence of magnetic layered van der Waals (vdW) materials provides a wide playground to explore the exotic magnetism arising in the two-dimensional (2D) limit. The magnetism of 2D flakes, especially antiferromagnetic ones, however, cannot be easily probed by conventional magnetometry techniques, being often replaced by indirect methods like Raman spectroscopy. Here, we make use of an alternative approach to provide direct magnetic evidence of few-layer vdW materials, including antiferromagnets. We take advantage of a surfactant-free, liquid-phase exfoliation (LPE) method to obtain thousands of few-layer FePS3 flakes that can be quenched in a solvent and measured in a conventional SQUID magnetometer. We show a direct magnetic evidence of the antiferromagnetic transition in FePS3 few-layer flakes, concomitant with a clear reduction of the Néel temperature with the flake thickness, in contrast with previous Raman reports. The quality of the LPE FePS3 flakes allows the study of electron transport down to cryogenic temperatures. The significant through-flake conductance is sensitive to the antiferromagnetic order transition. Besides, an additional rich spectra of electron transport excitations, including secondary magnetic transitions and potentially magnon-phonon hybrid states, appear at low temperatures. Finally, we show that the LPE is additionally a good starting point for the mass covalent functionalization of 2D magnetic materials with functional molecules. This technique is extensible to any vdW magnetic familyE.B. acknowledges funds from Ministerio de Ciencia e Innovación in Spain (RTI2018-096075-A-C22, RYC2019- 028429-I). E.M.P. thanks the Spanish Ministerio de Ciencia e Innovación (PID2020-116661RB-I00) and Comunidad de Madrid (P2018/NMT-4367). M.G.H. and A.C.-G. acknowledge funds from European Union Horizon 2020 research and innovation program (Graphene Core3-Grant agreement no. 881603 Graphene-based disruptive technologies), EU FLAGERA through the project To2Dox (JTC-2019-009), and Comunidad de Madrid through the project CAIRO-CM project (Y2020/NMT-6661). A.C.-G. also acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 755655, ERC-StG 2017 project 2D-TOPSENSE) and the Ministry of Science and Innovation (Spain) through the project PID2020-115566RB-I00. M.L.R.G. acknowledges support by the Spanish Ministry of Science and Innovation through Research Project PID 2020- 113753RB-100. The National Centre for Electron Microscopy (ELECMI National Singular Scientific Facility) is also acknowledge for provision of access to corrected aberration microscopy facilities. CzechNanoLab Research Infrastructure supported by MEYS CR (LM2018110) is acknowledge