Eva M. García-Frutos

Instituto de Ciencia de Materiales de Madrid, Madrid, Madrid, Spain

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Publications (25)69.03 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    The Journal of Physical Chemistry C. 02/2014; 118(10):5470–5477.
  • Eva M. Garcia-Frutos
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    ABSTRACT: 1D π-conjugated organic micro- or nanostructures keep all the advantages found in organic single crystals, e.g. high crystallinity, but without the tricky growth associated with large-sized crystals. They also present low-cost processing, solution processable materials, and large-area fabrication, and are compatible with flexible substrates. Electronic and optical properties of 1D π-conjugated organic micro- and nanomaterials can be tuned by changing their size at the central core or chemical modification of the aromatic substituents, among other alternatives. Current challenges are to find and develop an accurate control of the morphology, size, degree of uniformity, and alignment of the micro- and nanometer-sized organic single crystals, for future applications in miniaturized devices.
    J. Mater. Chem. C. 05/2013; 1(23):3633-3645.
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    ABSTRACT: We report on a new p-type organic semiconductor single crystal, 5,10,15-trimethyl-10,15-dihydro-5H-diindolo[3,2-a:3’,2’-c]carbazole (N-trimethyltriindole). This molecule crystallizes forming a highly ordered columnar structure in which stacked molecules are situated at two alternating distances (3.53 Å and 3.68 Å) along the column as determined by single crystal X-ray diffraction analysis. These short intermolecular distances between adjacent units, make this system an ideal candidate for charge-transport processes along the stacks.Relevant parameters for transport (i.e. internal reorganization energies, transfer integral) have been estimated by DFT calculations at a 6-311G(d,p)/B3LYP level of theory. As a double check for the transfer integral, the electronic band structure of a one-dimensional stack of molecules has been computed. The electronic properties of this material have been studied both theoretically and experimentally. Its HOMO value is found to coincide with Au work function (ΦAu = 5.1 eV), thus low barriers are expected for hole injection from gold electrodes. The hole mobility of this material has been predicted theoretically considering a hopping-type mechanism for the charge-transport and determined experimentally at the space charge limited current (SCLC) regime of the current–voltage measurements. Both theoretical and experimental values are in good agreement. The high hole mobility (μmin = 0.4 cm2 V−1 s−1) of this material points towards its useful application in the organic electronics arena. N-Trimethyltriindole single crystals constitute an essential model to study transport properties of triindole-based materials and to design new derivatives with improved electronic performance.
    Organic Electronics 04/2013; · 3.84 Impact Factor
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    ABSTRACT: A set of chiral discotic phenylacetylenes has been synthesized by threefold Sonogashira-coupling between different ethynylbenzenes and triiodobenzenes. The resultant bulk materials are fully characterized by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction. The octopolar nature of the target compounds is studied by UV-Vis absorption spectroscopy and hyper-Raleigh-scattering in solution. Optimization of the donor-acceptor substitution yields both, high hyperpolarizability values and appreciable mesomorphic properties. A simple thin film device for second harmonic generation has been prepared from the nitro-substituted liquid crystalline derivative.
    The Journal of Organic Chemistry 11/2012; · 4.56 Impact Factor
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    ABSTRACT: Chemists worldwide are making strong efforts toward finding an organic semiconductor with optimum charge-transport stability and processability properties, approaching the problem from several angles. The number and variety of organic semiconductors have expanded exponentially during the past few years, allowing their classification and identification of the advantages and drawbacks of the different candidates, and leading to an increasingly better understanding of factors affecting charge carrier mobility. In this Perspective, we present different types of materials available, classified according to their supramolecular order. As it will be shown, high intermolecular order, although beneficial for charge transport, may compromise processability. The required balance between processing and high mobility can be achieved only through an adequate design at both the molecular and supramolecular levels.
    06/2012;
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    ABSTRACT: A comprehensive series of systematically functionalized C3-symmetric hexakis (para-substituted) triindoles has been studied for its linear and second-order nonlinear optical properties. The carbazole-derived triindole central core is electron rich and electron donating. The peripheric substitution pattern, resulting in a donor–donor or a donor–acceptor charge transfer, is reflected in the UV–vis absorption spectra, where a lower energy charge-transfer band is observed for the donor–acceptor pattern. On-resonance all compounds exhibit a strongly enhanced second-order nonlinear optical response, critically dependent on the particular wavelength but showing no clear correlation with the charge-transfer character imparted by the peripheral substituents. Nonetheless, extremely large values are obtained: we measured the highest value ever reported for octupolar compounds in transparent conditions on-resonance. Off-resonance significantly smaller values are found, which are very similar for all compounds and show no correlation with the charge-transfer character as well. Both observations have been unambiguously confirmed by (linear and nonlinear) spectroelectrochemistry on a donor–donor structure, effectively transforming this to an acceptor–donor structure (by oxidizing the donor triindole core to an electron-accepting triindole-based cation radical). The strong wavelength dependence of the first hyperpolarizability values around resonance is clearly shown to be overwhelmed by dispersion effects and not to be determined by the charge-transfer pattern in these octupolar materials. This finding provides insight for independent tuning of the linear absorptive properties, determined by the charge-transfer pattern, and the second-order nonlinear polarizability, not determined by this pattern but strongly dispersive.
    The Journal of Physical Chemistry C. 05/2012; 116(22):12312–12321.
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    ABSTRACT: We report the synthesis, mesomorphic behavior, and mobility values of a series of highly ordered N-substituted triindole-based columnar liquid crystals. Shortening the length of N-alkylic substituents from N-dodecyl to N-methyl chains results in a drastic approach of the disks within the columns and in an impressive increase in charge carrier mobility. An study of aggregation in solution provide insights into the intermolecular forces responsible of the reduction of the intrastack distance as the size of the N-alkyl chains is decreased and offer evidence of stabilization of the columns by the contribution of cooperative CH−π interactions. The materials presented here exhibit mobility values, even in totally misaligned columnar phases, that may compete with those of the best polycrystalline organic semiconductors, without the need of costly vacuum evaporation processes.
    Chemistry of Materials. 01/2012; 25(2):117-121.
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    ABSTRACT: We present a series of differently substituted star-shaped hexaaryltriindoles with tunable light-emitting properties. The deep blue emission is unchanged by donor peripheral substituents while an increasing acceptor character produces a reduction of the optical gap, an increased Stokes shift and eventually leads to the appearance of a new electronic level and to the simultaneous deep blue (413 nm) and green (552 nm) emission in solution. Quenching by concentration increases with the acceptor character but is lower as the tendency of these compounds to aggregate is stronger. Solution processed thin films present optical and morphological qualities adequate for device fabrication and similar electronic structure compared to solutions with an emission range from 423 nm up to 657 nm (red), demonstrating the possibility of tuning the energy levels by chemical functionalization. We have fabricated and characterized single-layer solution processed organic light emitting diodes (OLED) to investigate the influence on transport and emission properties of the substituting species. We analyzed the I–V response using a single-carrier numerical model that includes injection barriers and non-uniform electric-field across the layer. As a result, we obtained the electric field dependence of the mobility for each device. Best results are obtained on the most electron rich derivative functionalized with six donor methoxy groups. This material shows the highest emission efficiency in solid state, due to aggregation-induced enhancement, and better transport properties with the highest mobility and a very low turn-on voltage of 2.8 V. The solution processed OLED devices produce stable deep blue (CIE coordinates (0.16, 0.16)) to white (CIE coordinates (0.33, 0.3)) emission with similar luminous efficiencies.
    Organic Electronics 01/2012; 13(10):2138. · 3.84 Impact Factor
  • Angewandte Chemie International Edition 06/2011; 50(32):7399-402. · 11.34 Impact Factor
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    ABSTRACT: New π-extended discotic liquid crystals based on heptacyclic triindole have been synthesized and their mesomorphic behaviour investigated. The synthesis of π-extended compounds was carried out by oxidative cyclodehydrogenation of differently substituted star-shaped hexaaryltriindoles to afford the planar derivatives with an extended core. Extending the conjugation in these materials results in a significant increase in the order and range of the mesophases. The influence of the peripherally attached groups in the mesomorphic and electronic properties offers a great opportunity to further tune the properties of these compounds intended to their incorporation in devices.
    Journal of Materials Chemistry 04/2011; 21(19):6831-6836. · 5.97 Impact Factor
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    ABSTRACT: We introduce a new family of stable high-mobility organic π-type semiconductors based on the electron-rich 10,15- dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole (triindole) extended π-conjugated system. This platform tends to form columnar stacks of the aromatic cores maximizing π-orbital overlap between adjacent molecules, thus paving the way for the one-dimensional migration of charge carriers along the columns. In addition these compounds have two different types of positions that can be functionalized independently offering the possibility of tuning their electronic properties as well as their morphology through chemical functionalization. The integration of the optimized triindole derivatives into solution processed devices as active layer is explored in this work.
    Proc SPIE 08/2010;
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    ABSTRACT: The synthesis and aggregation properties of a series of differently substituted star-shaped hexaaryltriindoles both in solution and in the solid state are being reported. While these molecules do not show any significant intermolecular aggregation in CDCl(3), it has been possible to induce aggregation by increasing the polarity of the solvent and therefore facilitating the occurrence of solvophobic forces. A study of the influence of the electronic character of peripheral substituents on the self-association behavior in solution has shown that increasing the electron-donor character of the substituents facilitates self-association while derivatives substituted with electron-acceptor substituents do not self-assemble. The electronic nature of the substituents also has an influence in the geometry of the stacking of these derivatives observed in the solid state. While unsubstituted hexaphenyl triindole self-assemble in a staggered face-to-face arrangement, attaching six cyano functional groups results in an offset stacking. The influence of the substituents in the strength and geometry of the stacking tendency contrasts with the trend expected for an aggregation induced solely by pi-pi interactions, but can be explained considering an important contribution of multiple cooperative CH-pi interactions.
    The Journal of Organic Chemistry 02/2010; 75(4):1070-6. · 4.56 Impact Factor
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 31(33).
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    ABSTRACT: The search of new organic molecules with improved properties is of fundamental relevance for hybrid organic-inorganic based devices (OLED, FET, PV, injection layers, flexible large area devices, lasers, etc.). Triindole based materials present extended aromatic cores with disk-like geometry that allow tailoring their electronic properties through chemical functionalization. In this work we present an optical and electronic study of new triindole based single crystals. Pistacking gives rise to highly ordered columnar structures yielding to high mobilities, around 0.4 cm2V-1s-1. External oxidation is found to increase orders of magnitude the conductivity. Slight modifications of this platform modify substantially the crystallization dynamics and therefore the quality of the thin films obtained by spin coating from solutions with different solvents. The morphology, stability and properties of the optimized films are found to be promising for device fabrication. A comparative study of the absorption and emission efficiency of solutions and thin films of the different derivatives is presented. The first tests for OLED and OFET devices are under way.
    Proc SPIE 08/2009;
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    E. M. García-Frutos, B. Gómez-Lor
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    ABSTRACT: Much effort is being dedicated to develop small organic molecules for their use in organic electronic devices, for which a key parameter is the mobility of charge within the active organic layers. Important advances achieved in this field have been therefore connected to the enhancement of the charge carrier mobility of organic semiconductors. In this communication we present a new family of stable high-mobility organic p-type semiconductors based on the electronrich 10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole (triindole) platform. We show how it is possible to tune their electronic properties as well as their supramolecular organization through chemical functionalization.
    Proc SPIE 08/2009;
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    ABSTRACT: PbII ethynyl- and butadiynyl-bridged bis(phthalocyaninates) 1a–d, peripherally functionalized with n-butoxy moieties, have been synthesized by using Pd-catalyzed cross-coupling methodologies. Preliminary open-aperture Z-scan experiments with nanosecond pulses at 550 nm on solutions of PbII bis(phthalocyaninates) 1b and 1d show strong reduction of the transmission at high intensities, although an irreversible optical behaviour is observed at the experimental time scale. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
    Annalen der Chemie und Pharmacie 05/2009; 2009(19):3212 - 3218. · 3.10 Impact Factor
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    ABSTRACT: A new series of C(3)-symmetrical N-(hetero)arylmethyl triindoles has been synthesized in a straightforward procedure. The structure and conformation in the solid state have been determined for three derivatives (3, 4, and 6) by X-ray crystallographic analysis. In all three cases, the molecules adopt a tripodal conformation with all of the flexible arms directed towards the same side, thereby delimiting an inner cavity. Compound 6 crystallizes and forms C(3)-symmetric dimeric cagelike complexes. Guest molecules of chloroform and water are confined within the resulting cavities with stabilization by different intermolecular interactions; this highlights the potential of these compounds in the construction of supramolecular systems. A computational analysis has been performed to predict the most stable conformers. As a general trend, a preference for a conformation with all branches directed to the same side has been predicted. Comparison between theoretical and experimental results indicates that the computational level selected for the present study, B3LYP/6-31G*, is able to reproduce both the minimum energy conformations and the rotation barriers about the N--CH(2) bond.
    Chemistry 09/2008; 14(28):8555-61. · 5.83 Impact Factor
  • Eva M García-Frutos, Berta Gómez-Lor
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    ABSTRACT: A number of differently substituted phenylethynyl triindoles has been synthesized by 6-fold Sonogashira coupling in a key step. This new series of hexaalkynyl triindoles self-associate through arene-arene interactions in solution. The electronic communication of the external substituents with the central electron-rich triindole core has been demonstrated by means of cyclic voltammetry and optical absorption. A study of the effect of the electronic character of peripheral substituents on their self-association behavior is presented in an effort to shed light on the nature of the pi-stacking interactions.
    Journal of the American Chemical Society 08/2008; 130(28):9173-7. · 10.68 Impact Factor
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    ABSTRACT: Two functionalized phthalocyanine-based chromophore systems having two iodophthalocyaninatozinc(II) rings bound together through a butadiynyl linkage 1a,b have been synthesized by oxidative Eglinton coupling of the corresponding monomer, and fully characterized. The electronic characteristics of these extensively linearly pi-conjugated compounds were modulated by the introduction of different peripheral substituents into the phthalocyanine moieties and investigated by UV-visible spectroscopy. The reactivity of the two iodo substituents was explored to prepare a novel bisphthalocyanine containing two ethynylphenyl moieties, thus pointing out the possibility of incorporating other electro and/or photoactive moieties in the BisPc system, taking advantage of the iodo-functionalization.
    Journal of Inorganic Biochemistry 04/2008; 102(3):388-94. · 3.20 Impact Factor
  • Chemistry of Materials - CHEM MATER. 01/2008; 20(21):6589-6591.

Publication Stats

50 Citations
69.03 Total Impact Points

Institutions

  • 2011–2014
    • Instituto de Ciencia de Materiales de Madrid
      Madrid, Madrid, Spain
  • 2013
    • University Carlos III de Madrid
      Getafe, Madrid, Spain
  • 2008–2013
    • Spanish National Research Council
      • Instituto de Ciencia de Materiales de Madrid
      Madrid, Madrid, Spain
  • 2000–2009
    • Universidad Autónoma de Madrid
      • • Departamento de Química Orgánica
      • • Facultad de Ciencias
      Madrid, Madrid, Spain