Computations on electroactive molecular materials: from donor–acceptor architectures to supramolecular polymers

En la presente tesis, se ha realizado un estudio teórico exhaustivo sobre una gran variedad de sistemas moleculares electroactivos con propiedades ópticas, electónicas y de autoensamblaje interesantes para ser explotadas en electrónica molecular y ciencia de nuevos materiales. Los resultados del trabajo de investigación se resumen en tres secciones de acuerdo con: Arquitecturas dador–acceptor covalentes Se han caracterizado teóricamente las propiedades electrónicas y ópticas de cromóforos dador–aceptor que absorben luz en todo el espectro visible. En particular, los cálculos DFT han proporcionado información sobre los regioisómeros más interesantes de exTTF-DCF para obtener un máximo beneficio en celdas solares sensibilizadas con colorantes (DSCs). Los tres regioisómeros posibles muestran características de absorción equivalentes en comparación con el análogo exTTF-TCF, con bandas de transferencia de carga intensas de baja energía calculadas en el intervalo visible. El derivado exTTF-DCF-A ha demostrado ser el colorante más prometedor debido a su anclaje más estable y su disposición perpendicular al unirse al semiconductor de TiO2. Asimismo, se han investigado cromóforos di-ramificados basados en el fragmento dador de hemiexTTF, que muestran bandas de transferencia de carga de baja energía y un desplazamiento al rojo de la absorción tras la inclusión del puente π-conjugado EDOT entre las unidades dador y aceptor. Los cálculos de primeros principios demuestran que el modo de adsorción más plausible de los colorantes di-ramificados sustituidos con carboxilo en dióxido de titanio es una coordinación monodentada del grupo ácido cianoacrílico en ambas ramas de anclaje. Esta coordinación cuenta con el anclaje más estable del colorante di-ramificado a la superficie del semiconductor, así como con dos amplias e intensas bandas LUMO que mejorarían la inyección de electrones en el semiconductor. Complejos dador–aceptor supramoleculares Se han estudiado complejos supramoleculares dador–aceptor bajo el marco DFT incluyendo correcciones de dispersión para ayudar a racionalizar el origen de las fuerzas que guían el autoensamblaje de nanoformas de carbono por receptores electroactivos. Los cálculos teóricos muestran que la incompatibilidad convexo–planar entre los anfitriones de porfirina y un derivado de fullereno C60 queda superada por fuertes interacciones no covalentes, que muestran una naturaleza electrostática predominante tras la sustitución metálica en la porfirina. Cálculos químico–cuánticos de receptores de porfirina ditópicos de fullereno C60 confirman una reducción de la densidad electrónica del receptor tras la inclusión del primer huésped de fullereno, de acuerdo con la cooperatividad negativa encontrada experimentalmente para estos sistemas. De forma interesante, la cinta de porfirina ditópica puede acomodar la segunda bola de C60 en una posición syn o anti. Los cálculos de primeros principios demuestran que la disposición syn es ~ 5 kcal mol−1 más estable, hecho que se explica por una interacción π–π estabilizante entre las dos bolas de fullereno que compensa parcialmente la cooperatividad negativa. Por otra parte, los agregados supramoleculares cóncavo-cóncavo inesperados se han calculado como los ensamblajes más estables para los complejos dador–aceptor de truxTTF•buckybowl. En estas configuraciones, no sólo interacciones π–π sino especialmente contactos CH···π son prominentes. Las estimaciones de energía libre para la asociación dador–aceptor indican que sólo los agregados escalonados (cóncavo–cóncavo) se forman en disolución, en buen acuerdo con la información de RMN experimental. Los cálculos teóricos confirman la existencia de bandas de transferencia de carga débiles a bajas energías descritas por la promoción de un electrón desde el dador de electrones truxTTF al buckybowl, que actúa como aceptor. La existencia de las correspondientes especies de separación de carga tras la fotoexcitación se ha confirmado mediante técnicas espectroscópicas en una fructífera colaboración con grupos de investigación experimental. Polímeros Supramoleculares Se han utilizado bloques de construcción electroactivos de tipo discótico para analizar teóricamente las propiedades de autoensamblaje en polímeros supramoleculares gobernados por interacciones no covalentes. En particular, se han calculado trisamidas N-centradas que sufren agregación supramolecular en forma de hélices columnares guiadas por interacciones π–π entre los núcleos aromáticos y, especialmente, por una red triple de enlaces de H entre las amidas. Este patrón de enlaces de H es el responsable de la cooperatividad del proceso de polimerización, que provoca un incremento en la energía de asociación y momento dipolar por unidad monomérica al aumentar el tamaño del polímero. El enfoque teórico multi-nivel empleado inequívocamente ha permitido la identificación del sentido helicoidal en función de la cadena alifática estereogénica, e indica un efecto insignificante de la conectividad de los grupos amida en la orientación helicoidal resultante. Por otro lado, se han estudiado derivados de pirenoimidazol que promueven el autoensamblaje en forma de organogeles con una emisión azul inesperada. Los cálculos teóricos demuestran, en sinergia con las evidencias experimentales, que el proceso de autoensamblaje se rige por las interacciones de los enlaces de H entre los grupos imidazol y amida junto con un gran número de interacciones CH···π entre la cadena alifática y los núcleos aromáticos de pireno. La ausencia de interacciones π–π entre los núcleos de pireneimidazol permite además explicar la preservación de las características de emisión de azul que exhiben dichos derivados tras la polimerización

Computational modeling of single- versus double-anchoring modes in di-branched organic sensitizers on TiO2 surfaces: structural and electronic properties

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Charge-transfer interactions between fullerenes and a mesoporous tetrathiafulvalene-based metal-organic framework

The design of metal-organic frameworks (MOFs) incorporating electroactive guest molecules in the pores has become a subject of great interest in order to obtain additional electrical functionalities within the framework while maintaining porosity. Understanding the charge-transfer (CT) process between the framework and the guest molecules is a crucial step towards the design of new electroactive MOFs. Herein, we present the encapsulation of fullerenes (C60) in a mesoporous tetrathiafulvalene (TTF)-based MOF. The CT process between the electron-acceptor C60 guest and the electron-donor TTF ligand is studied in detail by means of different spectroscopic techniques and density functional theory (DFT) calculations. Importantly, gas sorption measurements demonstrate that sorption capacity is maintained after encapsulation of fullerenes, whereas the electrical conductivity is increased by two orders of magnitude due to the CT interactions between C60 and the TTF-based framework

CarbonNanotubesConjugatedwithTriazole-BasedTetrathiafulvalene-TypeReceptorsfor C60Recognition

Fullerene receptors prepared by a twofold CuI -catalyzed azide-alkyne cycloaddition (CuAAC) reaction with -extended tetrathiafulvalene (exTTF) have been covalently linked to singlewalled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The nanoconjugates obtained were characterized by several analytical, spectroscopic and microscopic techniques (TEM, FTIR, Raman, TGA and XPS), and evaluated as C60 receptors by UV-Vis spectroscopy. The complexation between the exTTF-triazole receptor in the free state and C60 was also studied by UV-Vis and 1 H NMR titrations, and compared with analogous triazole-based tweezer-type receptors containing the electron-acceptor 11,11,12,12-tetracyano-9,10-anthraquinodimethane (TCAQ) and benzene rings instead of exTTF motifs, providing in all cases very similar values for the association constant (log Ka 3.0‒3.1). Theoretical density functional theory (DFT) calculations demonstrated that the enhanced interaction between the host and the guest upon increasing the size of the -conjugated arms of the tweezer is compensated by an increase in the energy penalty needed to distort the geometry of the host to wrap C60

Selective CO2 sorption using a compartmentalized coordination polymers with discrete voids

Carbon capture and storage with porous materials is one of the most promising technologies to minimize CO2 release into the atmosphere. Here, we report a family of compartmentalized coordination polymers (CCPs) capable of capturing gas molecules in a selective manner based on two novel tetrazole-based ligands. Crystal structures have been modelled theoretically under the Density Functional Theory (DFT) revealing the presence of discrete voids of 380 Å3. Single gas adsorption isotherms of N2, CH4 and CO2 have been measured, obtaining a loading capacity of 0.6, 1.7 and 2.2 molecules/void at 10 bar and at 298 K for the best performing material. Moreover, they present excellent selectivity and regenerability for CO2 in mixtures with CH4 and N2 in comparison with other reported materials, as evidenced by dynamic breakthrough gas experiments. These frameworks are therefore great candidates for separation of gas mixtures in the chemical engineering industry

Dual-mode chiral self-assembly of cone-shaped subphthalocyanine aromatics

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/jacs.0c07291Columnar polymers and liquid crystals obtained from π-conjugated cone-shaped molecules are receiving increasing interest due to the possibility of obtaining unconventional polar organizations that show anisotropic charge transport and unique chiroptical properties. However, and in contrast to the more common planar discotics, the self-assembly of conic or pyramidic molecules in solution remains largely unexplored. Here, we show how a molecular geometry change, from flat to conic, can generate supramolecular landscapes where different self-assembled species, each of them being under thermodynamic equilibrium with the monomer, exist exclusively within distinct regimes. In particular, depending on the solvent nature-aromatic or aliphatic-cone-shaped C3-symmetric subphthalocyanine 1 can undergo self-assembly either as a tail-to-tail dimer, showing monomer-dimer sigmoidal transitions, or as a head-to-tail noncentrosymmetric columnar polymer, exhibiting a nucleation-elongation polymerization mechanism. Moreover, the experimental and theoretical comparison between racemic and enantiopure samples revealed that the two enantiomers (1M and 1P) tend to narcissistically self-sort in the dimer regime, each enantiomer showing a strong preference to associate with itself, but socially self-sort in the polymer regime, favoring an alternate stacking order along the columnsFunding from the Spanish MINECO/MCIU [PGC2018-099568-B-I00, CTQ2017-85393-P, CTQ2017-84727-P, ERA-NET/European Commission/MINECO (UNIQUE, SOLAR-ERA.NET Cofund 2 N° 008/ PCI2019-111889-2), and RED2018-102331-T], the Generalitat Valenciana (SEJI/2018/035), and European Feder funds (PGC2018-099568-B-I00) is gratefully acknowledged. IMDEA Nanocien-cia acknowledges support from the “Severo Ochoa” Pro-gramme for Centres of Excellence in R&D (MINECO, Grant SEV2016-0686

Spin-Crossover Grafted Monolayer of a Co(II) Terpyridine Derivative Functionalized with Carboxylic Acid Groups

The synthesis and characterization of a new Co(II) spin-crossover (SCO) complex based on 4′-(4-carboxyphenyl)−2,2′:6′,2″-terpyridine ligand are reported. This complex can be successfully grafted on silver surface maintaining the SCO behavior. Thus, atomic force microscopy (AFM), matrix assisted laser desorption ionization - time-of-flight mass spectrometry (MALDI-TOF MS), Raman spectroscopy, and XPS measurements, upon surface deposition, evidence the formation of a monolayer of intact molecules grafted through carboxylate groups to the Ag surface. Three different techniques: Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), supported by first-principles calculations, confirm that the deposited molecules undergo a gradual spin transition with temperature. This phenomenon is unprecedented for a monolayer of molecules directly grafted onto a metallic surface from solution

Non-Centrosymmetric Homochiral Supramolecular Polymers of Tetrahedral Subphthalocyanine Molecules

This is the peer reviewed version of the following article: Angewandte Chemie - International Edition 54.8 (2015): 2543-2547, which has been published in final form at http://dx.doi.org/10.1002/anie.201411272. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-ArchivingA combination of spectroscopy (UV/Vis absorption, emission, and circular dichroism), microscopy (AFM and TEM), and computational studies reveal the formation of non-centrosymmetric homochiral columnar subphthalocyanine assemblies. These assemblies form through a cooperative supramolecular polymerization process driven by hydrogen-bonding between amide groups, π-π stacking, and dipolar interactions between axial B-F bondsFunding from MINECO (CTQ2011-24187, CTQ2011-23659, CTQ2011-23659 and 02, CTQ2012-31914, and CTQ2012-35513-C02-01), CAM (S2013/MIT-2841 FOTO-CARBON), GVA (PROMETEO/2012/053

Tuning the Optical Absorption of Sn-, Ge-, and Zn-Substituted Cs2AgBiBr6 Double Perovskites: Structural and Electronic Effects

Lead-free halide double perovskites (DPs) are highly tunable materials in terms of chemical composition and optical properties. One of the most widely reported DPs is Cs2AgBiBr6, which is envisaged as a promising absorber for photovoltaics. Nevertheless, its bandgap (around 1.9−2.3 eV) remains too large for common tandem solar cells. In this work, we report the mechanochemical synthesis of Sn-, Ge-, and Zn-substituted Cs2AgBiBr6 in powder form; their bandgaps reach 1.55, 1.80, and 2.02 eV, respectively. These differences are rationalized through density functional theory calculations, demonstrating combined electronic and structural (disorder) effects introduced by the divalent metal-cation substituents. Finally, we present the first vacuum-deposited thin films of the Sn-substituted DP, which also show a notable narrowing of the bandgap, and this paves the way toward its implementation in photovoltaic solar cells