Search

In this study, a set of 10 positional indolocarbazole (ICz) isomers substituted with dicyanomethylene groups connected via para or meta positions are computationally investigated with the aim of exploring the efficiency of structural isomerism and substitution position in controlling their optical and electronic properties. Unrestricted density functional theory (DFT), a spin-flip time-dependent DFT approach, and the multireference CASSCF/NEVPT2 method have been applied to correlate the diradical character with the energetic trends (i.e., singlet–triplet energy gaps). In addition, the nucleus-independent chemical shift together with ACID plots and Raman intensity calculations were used to strengthen the relationship between the diradical character and (anti)aromaticity. Our study reveals that the substitution pattern and structural isomerism represent a very effective way to tune the diradical properties in ICz-based systems with meta-substituted systems with a V-shaped structure displaying the largest diradical character. Thus, this work contributes to the elucidation of the challenging chemical reactivity and physical properties of diradicaloid systems, guiding experimental chemists to produce new molecules with desirable properties.

Carbon-bridged bis(aminoaryl) oligo(para-phenylenevinylene)s have been prepared and their optical, electrochemical, and structural properties analyzed. Their radical cations are class III and class II mixed-valence systems, depending on the molecular size, and they show electronic couplings which are among the largest for the self-exchange reaction of purely organic molecules. In their dication states, the antiferromagnetic coupling is progressively tuned with size from quinoidal closed-shell to open-shell biradicals. The data prove that the electronic coupling in the radical cations and the singlet–triplet gap in the dications show similar small attenuation factors, thus allowing charge/spin transfer over rather large distances.

Amphiphilic and lipophilic donor–acceptor naphthalimide–oligothiophene assemblies exhibiting almost identical intramolecular properties, but differing in their intermolecular interactions, have been synthesized. Here we analyze the effect of replacing the normally used lipophilic alkyl chains with hydrophilic ones in directing molecular aggregation from an antiparallel to a parallel stacking. This different molecular packing of the amphiphilic, NIP-3TAmphi, and lipophilic, NIP-3TLipo, systems is assessed by electronic spectroscopies, scanning electronic microscopy and DFT quantum-chemical calculations. Theoretical calculations indicate that the presence of amphiphilic interactions promotes a face-to-face parallel arrangement of neighbor molecules, which induces improved electronic coupling and therefore enhances the charge transport ability and photoconducting properties of this type of materials. Time of flight and photoconducting measurements are used to determine the impact of the amphiphilic and lipophilic interactions on their possible performance in optoelectronic devices.

We have performed a multiscale approach to study the influence of peripheral substitution in the semiconducting properties of discotic liquid-crystalline triindoles. Charge carrier mobility as high as 1.4 cm V s was experimentally reported for triindoles substituted with alkynyl chains on the periphery (Gómez-Lor et al. Angew. Chem., Int. Ed., 2011, 50, 7399-7402). In this work, our goal is to get a deeper understanding of both the molecular electronic structure and microscopic factors affecting the charge transport properties in triindoles as a function of the spacer group connecting the central cores with the external alkyl chains (i.e., alkyne or phenyl spacers groups). To this end, we first perform Quantum Mechanical (QM) calculations to assess how the peripheral substitution affects the electronic structure and the internal reorganization energy. Secondly, boxes of stacked molecules were built and relaxed through molecular dynamics to obtain realistic structures. Conformational analysis and calculations of transfer integrals for closed neighbours were performed. Our results show that the insertion of ethynyl spacers between the central aromatic core and the flexible peripheral chains results in lower reorganization energies and enhanced intermolecular order within the stacks with a preferred cofacial 60° staggered conformation, which would result in high charge-carrier mobilities in good agreement with the experimental data. This work allows a deeper understanding of charge carrier mobility in columnar phases, linking the structural order at the molecular level to the property of interest, i.e. the charge carrier mobility. We hope that this understanding will improve the design of systems at the supramolecular level aiming at obtaining a more defined conducting channel, higher mobility and smaller fluctuations within the column.

Radical cations and dications of [n]CPP from n = 5 to n = 12 have been studied by Raman spectroscopy and density functional theory. Small [n]CPP dications owe their stability to the closed-shell electronic structure imposed by cyclic conjugation surpassing the destabilizing effect of ring strain and of the electron deficiency of the charged states. Large [n]CPP dications mitigate cyclic strain by forming diradicals. The Raman spectra reflect the balance among cyclic conjugation, cyclic strain and biradicaloid stabilization by finding an unexpected turning point in the frequency behavior of the G vibrational modes as a function of size. These Raman data represent the vibrational fingerprint of this rare form of conjugation which is central to stabilize both cations and dications of [n]CPP macrocycles.

We present a joint theoretical and experimental study of a series of cyclic indole tetramers aimed at understanding the fundamental electronic properties of this 3D platform and evaluating its potential in the construction of new semiconductors. To this end, we combined absorption and Raman spectroscopy, cyclic voltammetry, and spectroelectrochemistry with DFT calculations. Our results suggest that this platform can be easily and reversibly oxidized. Additionally, it has a HOMO that matches very well with the workfunction of gold, therefore charge injection from a gold electrode is expected to occur without significant barriers. Interestingly, the cyclic tetraindoles allow for good electron delocalization in spite of their saddle-shaped structures. The steric constraints introduced by N-substitution significantly inhibits ring inversion of the central cyclooctatetraene unit, whereas it only barely affects the optical and electrochemical properties (a slightly higher oxidation potential and a blueshifted absorption upon alkylation are observed).

New dimers with two triindole subunits bound together through different linkers (p-phenylene or diacetylene groups) have been synthesized and studied as model systems to determine the differences in the electron transfer ability of the two bridging units. Our results show that whereas a p-phenylene bridge nearly isolates the two subunits of the dimers a diacetylene bridge allows a high level of electronic connection between them.

Estudio y Conservación del Patrímonio Cultural es el nombre del cuarto congreso promovido por la Red de Ciencia y Tecnología para la Conservación del Patrimonio Cultural (TechnoHeritqage). La Red, financiada cntre 2011 y 20]4 por la Acción Complemenlllfia HAR201O-11432-E, del Ministerio de Economía y Compctiti\tidad; llega a 2015 como gran parte de la economía española: mermada en lo económico, pero fuerte en cuanto se relaciona con el motor que impulsó su creación: el interés por el estudio y la conservación del Patrimonio Cultural, una herencia que trasciende a tas personas· de un lugar y momento determinado para cOJw¡;rtirse en propiedad de todos los seres humanos de todos los tiempos, presentes y venideros. En junio de 2011, recién nacida la iniciativa TechnoHeritage, tuvo lugar en Madrid, en la sede del Instituto del Patrimonio Cultural de España, la primera Reunión de la Red bajo el título de "Ciencia y Tecnología para la Conservación del Patrimonio Cultural". Concebida como un congreso nacional en el que !a prioridad fue dar u.n espacio a los diferentes grupos que comenzaron integrando la red para que se conocieran y pudieran exponer sus intereses, capacidades e instrumentación para poder cimentar colaboraciones y establecer una masa crítica que hiciera más fácil el acceso a diferentes proyectos y programas, nacionales y europeos. Fn¡to de esto fue la publicación de un primer libro de actas! en el que se publicaban 36 contribuciones. cada una rcferida a la actividad de uno de los grupos integrantes de la Red. La idea de que la Red debía ser una. plataforma que sirviera a todos los grupos para el establecimiento de relaciones tanto fonnales como informales, a nivel nacional. y europeo, se tradujo en la organización de dos congresos intcmadonales. El primero de ellos, organizado en 2012 en Santiago de Compostela b'\Ío el título "Science and Technology for the Conservation of Cultural Heritage", tuvo 160 asistentes de 10 países y dio origen a un libro de actas c, (i) M.A. Rogerjo~Candclern, e Saiz-]imenez (Eds.), Ciencia y Tecnologia para la Conservación de! Patrimonío cultural/. TechnoHeritage, Sevilla, 2011. (ii) M.A. Rogerio-Candelera, M. Lazzan, E. Cano (Eds.), Science and Technology for the conservation of cultural Heritage.CRC Press, Londres, 2013. (iii) M.A. Rogerio-Candelera (Ed.), Science, Technology and Cultural Heritage. CRC Press, Londres, 2014.

The electronic and photophysical properties of 6,11-dihydro-5H-diindolo[2, 3-a:2′,3′-c]carbazole, an asymmetric cyclic dehydrotrimer of indole, have been explored and compared to its symmetric analogue, 10,15-dihydro-5H- diindolo[3,2-a:3′,2′-c]carbazole (triindole), a well-known high hole mobility semiconductor. To this purpose, we use a joint experimental and theoretical approach that combines absorption and emission spectroscopies, cyclic voltammetry, and spectroelectrochemistry with DFT calculations. Lowering the symmetry of the triindole platform causes a red-shift of the absorption edge and emission maxima and improved the fluorescence quantum yield. Cyclic voltammetry and spectroelectrochemistry reveal the reversible nature of the two observable oxidation processes in the alkylated asymmetric triindoles together with an increase in the stabillity of their oxidized species. On the other hand, the insertion of alkyl groups on the nitrogen atoms results in a further fluorescence enhancement although larger reorganization energies are found. DFT and time-dependent (TD-DFT) calculations successfully support the experimental data and aid in the understanding of the tuning of the physicochemical properties of the triindole platform upon symmetry lowering toward their incorporation in electronic devices. © 2014 American Chemical Society.

Estado actual del conocimiento de la Sima del complejo kárstico de Palomas. Se ha presentado su enmarque geográfico y geológico y se ha valorado la historia de las investigaciones desarrolladas. Se han expuesto las actividades y tareas arqueológicas desarrolladas, así como una serie de analíticas científicas que ha realizado un equipo amplio de investigadores españoles y alemanes de diversas universidades y centros de investigación.

Amplified spontaneous emission (ASE) is observed, under optical pump, in polystyrene films doped with two pentathienoacene derivatives functionalised with thienyl-S,S-dioxide groups (compounds 2 and 3). The effect of the dioxide groups on the ASE properties is analysed by comparing the performance with that of its corresponding non-oxidized analogue (1). Films containing either 2 or 3 show ASE at 511 and 574 nm, respectively, when excited directly (at 435 nm) on their absorption bands, showing thresholds and linewidths larger than those obtained from films doped with 1, pumped at 355 nm. ASE is also observed under excitation at 355 nm, in samples containing 1 (host) and either 2 or 3 (guests), due to energy transfer from host to guest. For the blends with 3, the ASE threshold is lower than that obtained when the films are excited directly. Results are interpreted in terms of the photophysical parameters such as absorption capacity, fluorescence efficiency, singlet-to-triplet intersystem crossing leading to triplet-triplet re-absorptions, bimolecular energy-transfer efficiency, efficiency of internal conversion process, etc. State-of-the-art quantum chemical calculations are used in the interpretation of the experimental results.

Chromophores bearing a 2-dicyanomethylenethieno[3,2-b]thiophene moiety in their quinoidal form have been synthesized, exploring for the first time the reactivity of this system towards aldehydes. Their ground state polarization and linear and second-order nonlinear optical (NLO) properties have been determined by a combined experimental and theoretical study, and compared to those of analogous compounds featuring an aromatic thienothiophene unit. Due to the gaining of aromaticity, quinoid systems have been found to display more polarized electronic ground states and higher NLO responses with respect to their aromatic counterparts.

The vibrational, optical, and nonlinear optical (NLO) properties of a series of push-pull chromophores built around dithienylethylene-based (pi)-conjugating spacers have been investigated by UV-vis, IR, and Raman spectroscopies and electric field-induced second harmonic generation (EFISH) measurements. The effects of the strength of the acceptor group on the molecular electronic properties of these conjugated NLO chromophores have been addressed. The magnitude of the intramolecular charge transfer has been tested as a function of the acceptor strength and of the bridging of the spacer. Density functional theory (DFT) calculations have been performed to help the assignment of the main electronic and vibrational features of the NLO chromophores and to derive useful information about their molecular structures. EFISH measurements show that push-pull systems that contain strong electron-acceptor groups connected via a rigidified dithienylene spacer exhibit large values of uBo. Theoretical NLO calculations are in excellent agreement with experimental results. The geometrical and electronic properties calculated in solution reveal that chromophores become highly polarized as the dielectric constant of the solvent increases. The spectroscopic properties/structure relationships agree with the observation that Bo increases upon the covalent bridging of the spacer and with the increase of the acceptor strength.

The Raman spectra of a series of push-pull molecules containing probenzenoid or quinoid spacers which are substituted with 1,3-dithiol-2-ylidene as donor and dicyano-methylene or barbituric acid as acceptors have been analyzed. The experimental spectra have been assigned and interpreted according to density functional theory calculations. Correlations between the Raman spectra of the isolated spacers and of the substituted molecules have been done. Raman bands in the 1620-1560 cm-1 interval provide vibrational markers of the quinoid<-->aromatic structural evolution. This finding is supported by a careful inspection of geometrical parameters, namely, bond length alteration data and particular bond distances. As a result, the peak positions and relative intensities of these Raman features can be used to evaluate the benzenoid character of the spacer as a function of the donor/acceptor substitution pattern. This paper shows that Raman spectroscopy is a powerful spectroscopic tool for the analysis of the conjugational properties (i.e., intramolecular donor-->acceptor charge transfer) of new organic materials.

In this article, we present a computational study of the nonlinear optical properties of pyridine-based octupolar molecules in their neutral and fully triprotonated states. The effect of the core substitution and the degree of conjugation with the periphery has been also established and confirms the possibility of fine-tuning the nonlinear optical response. Computations involving the time-dependent density-functional theory approach serve to further explore the existence of excited states with nonzero dipole moment. From these results, the origin of the high second-order nonlinear optical activity upon protonation is addressed.

A series of tricyanovinyl (TCV)-substituted oligothiophenes was synthesized and investigated with a number of physical methods including UV/Vis, IR, and Raman spectroscopy, nonlinear optical (NLO) measurements, X-ray diffraction, and cyclic voltammetry. Mono- or disubstituted oligomers were prepared by the reaction of tetracyanoethylene with mono- or dilithiated oligomers. The comparative effects of the symmetric and asymmetric substitutions in the electronic and molecular properties have been addressed. These oligomers display dramatic reductions in both their optical and electrochemical band gaps in comparison with unsubstituted molecules. The analysis of the electronic properties of the molecules was assisted by density functional theory calculations, which are in excellent agreement with the experimental data. TCV substitution influences the energies of the frontier orbitals, especially with respect to the stabilization of LUMO orbitals. X-ray structural characterization of a monosubstituted oligomer exhibits -stacking with favorable intermolecular interactions. NLO results agree with the role of the intramolecular charge-transfer feature in the asymmetric samples. These results furthermore exalt the role of conformational flexibility in the disubstituted compounds and reveal an unexpected nonlinear optical activity for symmetric molecules. Regarding the electronic structure, the interpretation of the vibrational data reflects the balanced interplay between aromatic and quinoid forms, finely tuned by the chain length and substitution pattern. The electronic and structural properties are consistent with the semiconducting properties exhibited by these materials in thin film transistors (TFTs).