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Publications 2016


Modulation of the Exfoliated Graphene Work Function through Nitrile Imines Cycloaddition

M. Barrejón, M. J. Gómez-Escalonilla, J. L. G. Fierro, P. Prieto, J. R. Carrillo, A. M. Rodríguez, G. Abellán, M. C. López-Escalante, M. Gabás, T. López-Navarrete, F. Langa.

Physical Chemistry Chemical Physics, 2016, 18, 29582-29590.  DOI: 10.1039/C6CP05285A

After the feasibility of the 1,3-dipolar cycloaddition reaction between nitrile imines and exfoliated graphene by density functional theory calculations was proved, very few-layer graphene was effectively functionalized using this procedure. Hydrazones with different electronic properties were used as precursors for the 1,3-dipoles, and microwave irradiation as an energy source enabled the reaction to be performed in a few minutes. The anchoring of organic addends on the graphene surface was confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis. Ultraviolet photoelectron spectroscopy (UPS) was used to measure the work function and band gap of these new hybrids. Our results demonstrate that it is possible to modulate these important electronic valence band parameters by tailoring the electron richness of the organic addends and/or the degree of functionalization. 

Design of Assembled Systems Based on Conjugated Polyphenylene Derivatives and Carbon Nanohorns.

D. Iglesias, J. Guerra, M. V. Gómez, A. M. Rodríguez, P. Prieto, M. Prato, E. Vázquez, M. A. Herrero.

Chem. Eur. J., 2016, 22, 11643-11651. DOI: 10.1002/chem.201601282

Promising materials have been designed and fully characterised by an effective interaction between versatile platforms such as carbon nanohorns (CNHs) and conjugated molecules based on thiophene derivatives. Easy and non‐aggressive methods have been described for the synthesis and purification of the final systems. Oligothiophenephenylvinylene (OTP) systems with different geometries and electron density are coupled to the CNHs. A wide range of characterization techniques have been used to confirm the effective interaction between the donor (OTP) and the acceptor (CNH) systems. These hybrid materials show potential for integration into solar cell devices. Importantly, surface‐enhanced Raman spectroscopy (SERS) effects are observed without the presence of any metal surface in the system. Theoretical calculations have been performed to study the optimised geometries of the noncovalent interaction between the surface and the organic molecule. The calculations allow information on the monoelectronic energies of HOMO–LUMO orbitals and band gap of different donor systems to be extracted.

Diels–Alder reactions in confined spaces: the influence of catalyst structure and the nature of active sites for the retro-Diels–Alder reaction

Á. Cantín, M. V. Gomez, A. de la Hoz

Beilstein J. Org. Chem. 2016, 12, 2181–2188

Diels–Alder cycloaddition between cyclopentadiene and p-benzoquinone has been studied in the confined space of a pure silica zeolite Beta and the impact on reaction rate due to the concentration effect within the pore and diffusion limitations are discussed. Introduction of Lewis or Brønsted acid sites on the walls of the zeolite strongly increases the reaction rate. However, contrary to what occurs with mesoporous molecular sieves (MCM-41), Beta zeolite does not catalyse the retro-Diels–Alder reaction, resulting in a highly selective catalyst for the cycloaddition reaction.

Thematic issue on Green Chemistry. Editor. L. Vaccaro

New insights in the mechanism of the microwave-assisted Pauson-Khand reaction

A. M. Rodriguez, P. Prieto

New insights in the mechanism of the microwave-assisted PausoneKhand reaction

Tetrahedron 72 (2016) 7443-7448

A complete analysis of the stereoselectivity observed in the PausoneKhand reaction has been performed using computational calculations. The differences observed in the stereoselectivity when this reaction is performed either by conventional means or under microwave conditions have also been studied. The mechanisms suggested by MagnuseSchore and by Gimbert were used as a model in this investigation. The outcomes show that the observed diastereoselectivity is consistent with the mechanism proposed by Gimbert et al. Moreover, the high activation energy of the process could be responsible for the observed improvement under microwave irradiation.

Microwave Assisted Green Chemistry

A. de la Hoz, A. Díaz-Ortiz, P. Prieto

Alternative Energy Sources for Green Chemistry. Chapter 1. pp. 1-33

RSC Green Chemistry No. 47.

G. Stefanidis, A. Stankiewicz Eds.

Royal Society of Chemistry. ISBN: 9781782621409

Since the first publications on the use of microwave irradiation in synthetic chemistry, it was clear that this methodology would have a marked influence in all areas of this discipline. Reduction of reaction times, improved yields, modifications of selectivities, increased product purities and simplification of work-up procedures were described and, in most cases, these conditions and results could not be achieved by classical heating. This methodology can be included within the concept of Green Chemistry because the strong absorption of microwave irradiation by one component of the reaction would lead to shorter reaction times and improved energy efficiency. Moreover, the synergy with solvent-free conditions, solid catalysts and green solvents has expanded the green applications of this non-conventional energy source. Finally, the use of flow systems, another green methodology, has permitted the scale-up of microwave-assisted reactions under green conditions.

Triazine-Carbon Nanotubes: New Platforms for the Design of Flavin Receptors

M. I. Lucí†o, F. Pichler, J. R. Ramí†rez, A. de la Hoz, A. Sá‚nchez-Migallón, C. Hadad, M. Quintana, A. Giulani, M. V. Bracamonte, J. L. G. Fierro, C. Tavagnacco, M. A. Herrero, M. Prato, E. Vá‚zquez

Chem. Eur.J2016, 22,8879 –8888

The synthesis of functionalised carbon nanotubes as receptors for riboflavin (RBF) is reported. Carbon nanotubes, both single-walled and multi-walled, have been functionalised with 1,3,5-triazines and p-tolyl chains by aryl radical addition under microwave irradiation and the derivatives have been fully characterised by using a range of techniques. The interactions between riboflavin and the hybrids were analysed by using fluorescence and UV/Vis spectroscopic techniques. The results show that the attached functional groups minimise the π-π stacking interactions between riboflavin and the nanotube walls. Comparison of p-tolyl groups with the triazine groups shows that the latter have stronger interactions with riboflavin because of the presence of hydrogen bonds. Moreover, the triazine derivatives follow the Stern–Volmer relationship and show a high association constant with riboflavin. In this way, artificial receptors in catalytic processes could be designed through specific control of the interaction between functionalised carbon nanotubes and riboflavin.

Bistriazine-based streptocyanines. Preparation, structural determination and optoelectronic properties

F. León, P. Elizalde, P. Prieto, A. Sánchez-Migallón, A. M. Rodríguez, A. de la Hoz.

Dyes Pigments 2016, 131, 307–319
A series of bistriazine-based streptocyanines has been selectively prepared. A variety of substituents has been introduced into the triazine ring with p-phenylenediamine as a conjugated spacer between the triazine and the streptocyanine moieties. Fukui indices have been used to explain the different sequential reactivity of the chlorine atoms in the triazine ring. 1D- and 2D-DNMR spectroscopy and computational calculations have been carried out to explain the dynamic behavior of these complex systems, which can be explained by the presence of a Cl … H bond. This method was used to build conjugated systems and to show the interaction between the triazine part, the spacer, and the streptocyanine moiety. A study of the optoelectronic properties has been performed by UV–vis and fluorescence spectroscopy. Streptocyanine-based bistriazines are violet-blue emitters and large Stokes shifts of more than 6000 cm−1 were observed. The title compounds showed interesting properties which have potential for use in optoelectronic devices.

Synthesis of Imine-Derived Triazines with Donor-Acceptor Properties

D. R. Corrochano, A. de la Hoz, A. M. Sánchez-Migallón,, R. Caballero, J. R. Ramírez

J. Clean. Prod.  2016, 118, 223-226.

The design of new systems with Donor–Acceptor properties is of great interest for the construction of optoelectronic new devices. Considering the strong supramolecular interaction of triazines with graphene a series of imine-derived triazines with Donor–Acceptor properties have been designed. These compounds have been prepared in good to excellent yields (47–92%) using Green conditions, i.e. microwave irradiation in the absence of an acid catalyst. Their properties as Donor–Acceptor systems have been studied by Ultraviolet–visible and fluorescence spectroscopy and by electrochemical studies. These imine derived triazines are blue-violet emitters (ca. 396 nm) and show large Stokes shifts (c.a. 6700 cm−1) and the electrochemical studies shows a high degree of communication between the acceptor triazines and the donor moieties (oxidation potentials up to 1.10 V). These characteristics makes them excellent candidates for the interaction with graphene and the construction of optoelectronic devices, as blue Light Emitting-Diodes (LEDs).

Inside Cover: Stereoselective Synthesis of 1,3-Diaminotruxillic acid derivatives: An Advantageous Combination of CH-ortho-Palladation and on-flow [2+2]-photocycloaddition in microreactors.

Chem. Eur.J2016, 144–152

The stereoselective synthesis of 1,3-diaminotruxillic acid derivatives has been achieved in high yields and short reaction times. The procedure starts from simple 5(4H)- oxazolones and is based on an efficient combination of C[BOND]H orthopalladation, [2+2]-photocycloaddition on continuous flow microreactors using visible light from LED sources, and hydrogenation to selectively afford the epsilon isomer. More information can be found in the Full Paper by E. P. Urriolabeitia, M. V. Gómez, C. Cativiela et al. on page 144 ff.

Stereoselective Synthesis of 1,3-Diaminotruxillic acid derivatives: An Advantageous Combination of CH-ortho-Palladation and on-flow [2+2]-photocycloaddition in microreactors.

Elena Serrano, Alberto Juan, Angel Garcia-Montero, Tatiana Soler, Francisco Jimenez-Marquez, Carlos Cativiela, M. Victoria Gomez, Esteban Urriolabeitia

Chem. Eur.J.2016, 22,144 –152

The stereoselective synthesis of ε-isomers of dimethyl esters of 1,3-diaminotruxillic acid in three steps is reported. The first step is the ortho-palladation of (Z)-2-aryl-4-aryliden-5(4H)-oxazolones 1 to give dinuclear complexes 2 with bridging carboxylates. The reaction occurs through regioselective activation of the ortho-C[BOND]H bond of the 4-arylidene ring in carboxylic acids. The second step is the [2+2]-photocycloaddition of the C[DOUBLE BOND]C exocyclic bonds of the oxazolone skeleton in 2 to afford the corresponding dinuclear ortho-palladated cyclobutanes 3. This key step was performed very efficiently by using LED light sources with different wavelengths (465, 525 or 625 nm) in flow microreactors. The final step involved the depalladation of 3 by hydrogenation in methanol to afford the ε-1,3-diaminotruxillic acid derivatives as single isomers.

Green Synthesis of luminescent blue emitters based on bis-triazines with naphthalene as p-conjugated spacer

J. R. Ramírez, A. Ruiz-Carretero, M. Herrero. A. Sánchez-Migallón, A. de la Hoz

Dyes Pigments, 2016, 124, 203-209.

A new series of luminescent blue emissive bistriazines is described. Bistriazines with a naphthalene spacer were prepared using a green methodology that involved microwave irradiation, solvent free conditions and a reaction time of only 10 min. The synthesis was followed by a simple purification procedure. D-σ-A-σ-π-σ-A-σ-D systems were constructed using 1,5-naphthylidene as a planar π-bridge and different donor substituents were attached to the triazine ring. UV–vis and fluorescence spectroscopy showed that the increased conjugation in bistriazines with respect to monotriazines resulted in a 40-fold increase in the photoluminescence quantum yield (ΦF). The bistriazines were efficient blue emitters with ΦF values up to 0.87. The aggregation behavior and the optical and thermal properties of these systems have been studied. The bistriazines showed good thermal stability in conjunction with high ΦF values and they are therefore very promising materials for use in optoelectronic devices.

Self-assembly of T-shape 2H-benzo[d][1,2,3]-triazoles. Optical waveguide and photophysical properties

I. Torres, J. R. Carrillo, A. Díaz-Ortiz, R. Martín, M. V. Gómez, L. Stegemann, C. A. Strassert, J. Orduna, J. Buendía, E. E. Greciano, J. S. Valera, E. Matesanz, L. Sánchez, P. Prieto

RSC Adv., 2016, 6, 36544–36553

T-Shaped 2H-benzo[d][1,2,3]triazole derivatives have been synthesized by Sonogashira coupling reactions under microwave irradiation. DFT calculations were performed in order to understand the structure–property relationships – an aspect that is of vital importance for the rational design of organic selfassemblies for optoelectronic applications. Concentration-dependent 1H Pulse Field-Gradient Spin-Echo (PFGSE) NMR spectroscopy and UV/Vis spectrophotometry indicated the absence of a tendency for the aggregation of single molecules in solution. In contrast, in the solid state these compounds form organized aggregates and these were studied by scanning electron microscopy (SEM), which showed the influence that the peripheral substitution has on the morphology of the aggregates. For example, methoxy-substituted benzotriazoles self-assemble into thick and crystalline needle-like structures. However, the unsubstituted triazoles give rise to flower-like aggregates. Interestingly, the aggregates formed by benzotriazole 1c exhibit waveguide properties.