Ultrafast transient absorption spectroscopy: principles and applications

The study of photophysical and photochemical processes crosses the interest of many fields of research in physics, chemistry and biology. In particular, the photophysical and photochemical reactions, after light absorption by a photosynthetic pigment-protein complex, are among the fastest events in biology, taking place on timescales ranging from tens of femtoseconds to a few nanoseconds. Among the experimental approaches developed for this purpose, the advent of ultrafast transient absorption spectroscopy has become a powerful and widely used technique.[1,2] Focusing on the process of photosynthesis, it relies upon the efficient absorption and conversion of the radiant energy from the Sun. Chlorophylls and carotenoids are the main players in the process. Photosynthetic pigments are typically arranged in a highly organized fashion to constitute antennas and reaction centers, supramolecular devices where light harvesting and charge separation take place. The very early steps in the photosynthetic process take place after the absorption of a photon by an antenna system, which harvests light and eventually delivers it to the reaction center. In order to compete with internal conversion, intersystem crossing, and fluorescence, which inevitably lead to energy loss, the energy and electron transfer processes that fix the excited-state energy in photosynthesis must be extremely fast. In order to investigate these events, ultrafast techniques down to a sub-100 fs resolution must be used. In this way, energy migration within the system as well as the formation of new chemical species such as charge-separated states can be tracked in real time. This can be achieved by making use of ultrafast transient absorption spectroscopy. The basic principles of this notable technique, instrumentation, and some recent applications to photosynthetic systems[3] will be described. Acknowledgements M. Moreno Oliva thanks the MINECO for a “Juan de la Cierva-Incorporación” research contract. References [1] U. Megerle, I. Pugliesi, C. Schriever, C.F. Sailer and E. Riedle, Appl. Phys. B, 96, 215 – 231 (2009). [2] R. Berera, R. van Grondelle and J.T.M. Kennis, Photosynth. Res., 101, 105 – 118 (2009). [3] T. Nikkonen, M. Moreno Oliva, A. Kahnt, M. Muuronen, J. Helaja and D.M. Guldi, Chem. Eur. J., 21, 590 – 600 (2015).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

An approach to reconcile the agile and CMMI contexts in product line development

Software product line approaches produce reusable platforms and architectures for products set developed by specific companies. These approaches are strategic in nature requiring coordination, discipline, commonality and communication. The Capability Maturity Model (CMM) contains important guidelines for process improvement, and specifies "what" we must have into account to achieve the disciplined processes (among others things). On the other hand, the agile context is playing an increasingly important role in current software engineering practices, specifying "how" the software practices must be addressed to obtain agile processes. In this paper, we carry out a preliminary analysis for reconciling agility and maturity models in software product line domain, taking advantage of both.Postprint (published version

Valorization of keratin biofibers for removing heavy metals from aqueous solutions

Four common waste keratin biofibers (human hair, dog hair, chicken feathers, and degreased wool) have been used as biosorbents for the removal of heavy metal ions from aqueous solutions. Different parameters of the biosorption processes were optimized in batch systems. For multiple-metal systems, consisting of a mixture of eight metal ions [Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II)], the total metal biosorption increased in the order: degreased wool¿>¿chicken feathers¿>¿human hair¿>¿dog hair. From the kinetic models tested, the pseudo-second-order model provided better results. Furthermore, biosorption isotherms of Pb(II) with the different keratin biofibers fitted the Langmuir model. Surface morphology of the biosorbents were analyzed before and after the sorption using Fourier transform infrared spectroscopy and scanning electron microscopy. The keratin biofibers tested are potentially good sorbents of metal ions, with degreased wool and chicken feathers being the more efficient onesPostprint (author's final draft

Organic ambipolar semiconductors for TFT applications

In the last years we have devoted some effort to the search of new high-mobility semiconductors with ambipolar performances, good processability and environmental stability. Our approach, which is one of the most widely used, consists in the combination of donor and acceptor moieties in the conjugated skeleton, which allows fine tuning of the frontier molecular orbitals. For OTFT 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. In particular, we have combined naphthaleneimide-derived moieties as electron accepting groups with electron-rich oligothiophene fragments. In these materials, we have found that the presence of ambipolar transport in these planar molecules can be understood on the basis of three interrelated properties: (i) the absence of skeletal distortions allows closer intermolecular pi-pi stacking and enhanced intramolecular pi-conjugation, (ii) increased pi-conjugation raises the HOMO energy, which approaches the Fermi level of common used electrodes; and (iii) more planar structures translate into lower Marcus reorganization energies. However, one of the limitations of these types of semiconductors is the presence of a molecular dipole moment, which forces the molecules to pack with pairwise intermolecular interactions orienting the naphthaleneimide cores in opposite directions, decreasing in some cases molecular orbitals overlapping. In recent contributions, we have devoted our efforts to analyze the effect of molecular interactions, through chemical modifications in order to induce parallel and antiparallel molecular packing, on the electronic properties of ambipolar semiconductors.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Understanding organic materials performance in field-effect transistors

Comunicación oralIn the last years, much of our effort has been devoted to the search and study of new high-mobility semiconductors for organic thin film transistors. The approach used for the materials design has been two-fold: (i) the combination of donor and acceptor moieties in the pi-conjugated skeleton, which allows fine tuning of the frontier molecular orbitals, being this necessary for achieving electron/hole or ambipolar transport and ambient stability; and (ii) rational selection of the type and positioning of specific solubilizing substituents ensuring processability, which is essential to make these materials scalable to industry. However, material processability should be attained minimizing a negative effect on charge transport. Therefore, proper energy levels, planar molecular conformations, close intermolecular pi-pi stacking and adequate thin film crystallinity need to be maintained upon alkyl substitution. In this communication, several examples of molecular and polymeric materials are shown. A rational design, guided by experimental and theoretical evidences, has prompted modifications on their conjugated skeletons, donor/acceptor subunits ratio and/or selection of proper alkyl solubilizing chains, which induce noticeable changes in their electronic performances. The main aim of these studies is the basic understanding of charge transport in organic materials. For this end, we will use Raman spectroscopy and DFT quantum-chemical calculations as important tools for materials characterization.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Chiroptical Spectroscopy of C3 Molecules

The relevance of molecules with C3 symmetry comes from the fact of many of them, upon assembling as columnar helical macromolecules, are ideal platform for electro-optical devices, for example as liquid crystals. The properties of these devices are highly dependent of the structure of the bulk aggregates, and consequently they can be controlled by modifying the position and nature of the stereocenters in the molecular building blocks. In this work we present an electronic and vibrational chiroptical study on a series of star-shaped molecules based on the octopolar C3-symmetric 1,3,5-(phenylene-ethynylene)-benzene block.Universidad de Málaga, Campus de Excelencia Internacional Andalucía Tec

Raman Spectroscopy and DFT calculations for the Electronic Structure Characterization of Conjugated Polymers

Flash presentationIn the last three decades, there has been a broad academic and industrial interest in conjugated polymers as semiconducting materials for organic electronics. Their applications in polymer light-emitting diodes (PLEDs), polymer solar cells (PSCs), and organic field-effect transistors (OFETs) offer opportunities for the resolution of energy issues as well as the development of display and information technologies1. Conjugated polymers provide several advantages including low cost, light weight, good flexibility, as well as solubility which make them readily processed and easily printed, removing the conventional photolithography for patterning2. A large library of polymer semiconductors have been synthesized and investigated with different building blocks, such as acenes or thiophene and derivatives, which have been employed to design new materials according to individual demands for specific applications. To design ideal conjugated polymers for specific applications, some general principles should be taken into account, including (i) side chains (ii) molecular weights, (iii) band gap and HOMO and LUMO energy levels, and (iv) suited morphology.3-6 The aim of this study is to elucidate the impact that substitution exerts on the molecular and electronic structure of π-conjugated polymers with outstanding performances in organic electronic devices. Different configurations of the π-conjugated backbones are analyzed: (i) donor-acceptor configuration, (ii) 1D lineal or 2D branched conjugated backbones, and (iii) encapsulated polymers (see Figure 1). Our combined vibrational spectroscopy and DFT study shows that small changes in the substitution pattern and in the molecular configuration have a strong impact on the electronic characteristics of these polymers. We hope this study can advance useful structure-property relationships of conjugated polymers and guide the design of new materials for organic electronic applications.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Conjugated Polymers for Organic Electronics: Structural and Electronic Characteristics

The use of organic materials to design electronic devices has actually presented a broad interest for because they constitute an ecological and suitable resource for our current "electronic world". These materials provide several advantages (low cost, light weight, good flexibility and solubility to be easily printed) that cannot be afforded with silicium. They can also potentially interact with biological systems, something impossible with inorganic devices. Between these materials we can include small molecules, polymers, fullerenes, nanotubes, graphene, other carbon-based molecular structures and hybrid materials. Actually these materials are being used to build electronic structures into electronic devices, like organic light-emitting diodes (OLEDs), organic solar cells (OSCs), and organic field-effect transistors (OFETs), constituting and already commercial reality. Some of them are used on a widespread basis1, and are the focus of some recent researches in molecules2,3 and polymers4-6 suitable for these purposes. In this study we analyze the electronic and molecular characteristics of some different π-conjugated structures in order to evaluate their potential as semiconducting materials for organic electronics. For this purpose we focus on the study of conjugated polymers with different backbones configurations: (i) donor-acceptor configuration, (ii) 1D lineal or 2D branched conjugated backbones, and (iii) encapsulated polymers. To achieve this goal, we use a combined experimental and theoretical approach that includes electronic spectroscopies (i.e., absorption, emission and microsecond transient absorption), vibrational Raman spectroscopy and DFT calculations. These structural modifications are found to provoke a strong impact on the HOMO and LUMO levels and the molecular morphology, and, consequently, on their suitability as semiconductors in organic electronic applications.References 1. S. R. Forrest, M. E. Thompson. Chem. Rev., 2007, 107, 923 2. R. C. González-Cano, G. Saini, J. Jacob, J. T. López Navarrete, J. Casado and M. C. Ruiz Delgado. Chem. Eur. J. 2013, 19, 17165 3. J. L. Zafra, R. C. González-Cano, M. C. Ruiz Delgado, Z. Sun, Y. Li, J. T. López Navarrete, J. Wu and J. Casado. J. Chem. Phys. , 2014, 140, 054706 4. M. Goll, A. Ruff, E. Muks, F. Goerigk, B. Omiecienski, I. Ruff, R. C. González-Cano, J. T. López Navarrete, M. C. Ruiz Delgado, S. Ludwigs. Beilstein J. Org. Chem., 2015, 11, 335. 5. D. Herrero-Carvajal, A. de la Peña, R. C. González-Cano, C. Seoane, J. T. López Navarrete, J. L. Segura, J. Casado, M. C. Ruiz Delgado, J. Phys. Chem. C, 2014, 118, 9899. 6. M. Scheuble, Y. M. Gross, D. Trefz, M. Brinkmann, J. T. López Navarrete, M. C. Ruiz Delgado, and S. Ludwigs, Macromolecules, 2015, 48, 7049.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Cyclic Triindoles and Tetraindoles: Substituent and Symmetry Effects on their Structural and Electronic Characteristics

During the last decade heptacyclic 10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole (triindole) has been extensively studied as a new π-conjugated platform in the construction of self-assembling materials for optoelectronics. Specially remarkably is the record hole mobility values determined on triindole liquid crystals.1 In order to facilitate the design of new materials on a molecular basis and establish clear guidelines to fine tuning electronic parameters, we have recently synthesized new triindole and tetraindole-based systems.2-3 Our joint experimental and theoretical investigation shows that N-substitution, symmetry lowering of the platform, and insertion of π-spacers in extended dimers strongly impact on the fundamental electronic properties of triindoles.2 In addition, saddle-shaped tetraindoles are found to be an interesting 3D rigid scaffold to obtain electroactive molecules with increased dimensionality.3 We hope that this study can not only advance useful structure-property relationships of conjugated indole-based systems but also guide the design of new materials with potential applications in organic electronics.References 1. E.M. García-Frutos, U.K. Pandey, R. Termine, A. Omenat, J. Barberá, J.L. Serrano, A. Golemme, B. Gómez-Lor, Angew. Chem. Int. Ed. 2011, 50, 7399 2. a) C. Ruiz, J.T. López Navarrete, M.C.Ruiz Delgado, B. Gómez-Lor, Org. Lett. 2015, 17, 2258−2261. b) C. Ruiz, E.M. García-Frutos, D.A. da Silva Filho, J.T. López Navarrete, M.C. Ruiz Delgado, and B. Gómez-Lor, J. Phys. Chem. C 2014, 118, 5470−5477 3. C. Ruiz, A. Monge, E. Gutiérrez-Puebla, I. Alkorta, J. Elguero, J. T. López Navarrete, M.C. Ruiz Delgado and B. Gómez-Lor, submittedUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Chamber specific expression of Myosin heavy chain 7b in the heart of vertebrates

In extant vertebrates, myosin heavy chain (MyHC) 6 and 7 are the main isoforms of atrial and ventricular myocardium respectively, whereas MyHC7b has been proposed to be an ancient cardiac isoform only expressed during embryonic development in modern species. In preliminary immunohistochemical studies of the heart of the lesser spotted dogfish (Scyliorhinus canicula; Chondrichthyes), we have observed that while MF20 labels homogeneously all the myocardium, A4.1025 labels the inflow cardiac segments (sinus venosus and atrium) but not the outflow segments (ventricle and conus arteriosus). In order to interpret these results, we have performed western and slot blots from samples of dogfish and hamster (Mesocricetus auratus) hearts, HPLC-ESI-MS/MS from dogfish samples, and immunohistochemistry in hearts of representative species of vertebrates, namely elasmobranchs, polypteriforms, acipenseriforms, teleosts and mammals, using MF20 and A4.1025 antibodies. Western and slot blot results confirmed the specificity of MF20 and A4.1025 for MyHC in dogfish, as well as their differential reactivity against different myocardial segments. HPLC-ESI-MS/MS using protein databases from Callorhinchus milii (Chondrichthyes) and Chordata revealed the presence of MyHC6 and 7 in all the dogfish myocardial segments, and of MyHC7b only in the outflow segments. Immunohistochemistry showed that while MF20 signals were homogeneous in all the myocardial segments of all the species studied, A4.1025 signals were restricted to the inflow myocardial segments in elasmobranchs, homogeneous in teleosts and acipenseriforms, and low in the ventricle of polypteriforms. It can be inferred that the A4.1025 antibody, as opposed to MF20, has a low affinity for MyHC7b, at least in the dogfish. In addition, we show that MyHC distribution in the cardiac chambers has changed during the evolution of gnathostomes.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.Study supported by grants CGL2017-85090-P and CGL2014-52356-P (Ministerio de Economía y Competitividad), FPU15/03209 (Ministerio de Educación, Cultura y Deporte), contract UMAJI75 (Junta de Andalucía, European Social Found), FEDER and Universidad de Málaga