Publications 2015

Microwaves in Green and Sustainable Chemistry.

In Environment, Energy and Climate change I: Environmental Chemistry of Pollutants and Wastes. The Handbook of Environmental Chemistry. Vol. 32. Pp. 405-428. Springer. 2015. ISBN: 978-3-319-12906-8

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

4-Aryl-3,5-bis(arylethynyl)aryl-4H-1,2,4-triazoles: Multitasking Skeleton as a Self-Assembling Unit

M. J. Pastor, I. Torres, C. Cebrián, J. R. Carrillo, A. Díaz-Ortiz, E. Matesanz, J. Buendía, F. García, J. Barberá, P. Prieto, L. Sánchez

Chem. Eur. J. 2015, 21, 1795 – 1802

The synthesis of a series of 4-aryl-3,5-bis(arylethynyl) aryl-4H-1,2,4-triazoles derivatives is reported and the influence exerted by peripheral substitution on the morphology of the aggregates generated from these 1,2,4-triazoles is investigated by SEM imaging. The presence of paraffinic side chains results in long fibrillar supramolecular structures, but unsubstituted triazoles self-assemble into thinner ribbons and needle-like aggregates. The crystals obtained from methoxy-substituted triazoles have been utilised to elaborate a model that helps to justify aggregation of the investigated 1,2,4-triazoles, in which the operation of arrays of CH···p non-covalent interactions plays a significant role. The results presented herein demonstrate the ability of simple molecules to behave as multitasking scaffolds with different properties, depending on peripheral substitution. Thus, although 1,2,4-triazoles without long paraffinic side chains exhibit optical waveguiding behaviour, triazoles endowed with peripheral paraffinic side chains exhibit hexagonal columnar mesomorphism.

Synthesis of Bright 1H-1,2,4-triazoles. A theoretical and Photophysical Study

C. Cebrián, J. de M. Muñoz, C. A. Strassert, P. Prieto, A. Díaz-Ortiz, A. de la Hoz

ChemPlusChem, 2015, 79, 1489-1497

A sustainable synthesis of alkenyl-1H-1,2,4-triazoles through the Hiyama reaction is reported, which employs water as solvent and sodium hydroxide to activate the silyl group under microwave irradiation, thereby leading to high product yields (51–93 %) in very short reaction times. Two substitution patterns were attained owing to the different reactivity of the third and fifth positions of the 1H-1,2,4-triazole unit, as evidenced by calculated condensed Fukui functions. Moreover, all compounds are good blue emitters (Φ_F up to 0.69) in THF solution, although they exhibit an optical behavior dependent on the substitution. Excited-state theoretical investigations by the configuration interaction singles method and time-dependent density functional theory were performed not only to support and elucidate the studied photophysical properties, but also to create a predictive model to reduce the cost and optimize the search for new blue emitters based on this class of alkenyl-1H-1,2,4-triazoles.

Swivel-Cruciform Stilbenes Based on Bithiophene.

A. García-Rodríguez, A. M. Rodríguez, P. Prieto, R. Andreu, S. Merino, J. Rodríguez-López

Eur. J. Org. Chem., 2015, 2394-2404

Bithiophene-based cruciforms with different stilbenoid arms at the 3,3′- and 5,5′-positions have been synthesized by various combinations of Suzuki and Horner–Wadsworth–Emmons (HWE) reactions. According to DFT calculations, the steric hindrance between the arms at the 3,3′-positions produces a twist angle of 57.6° between the two thiophene rings that form the 2,2′-bithiophene unit, an arrangement that leads to a swivel-cruciform structure. The UV/Vis spectra contained strong absorption bands at wavelengths consistent with a twisted molecule with little interaction between the arms. The ability of these compounds to form highly stable radical cations was demonstrated by cyclic voltammetry and this, together with their good solubility in organic solvents, indicates that these materials have potential for the development of solution-processed electronic devices.

4-Aryl-3,5-bis(arylethynyl)aryl-4H-1,2,4-triazoles: Multitasking Skeleton as a Self-assembling Unit.

M. J. Pastor, I. Torres, C. Cebrián, J. R. Carrillo, A. Díaz-Ortiz, E. Matesanz, J. Buendía, F. García, J. Barberá, P. Prieto, L. Sánchez

Chem. Eur. J., 2015, 21, 1795-1802.

The synthesis of a series of 4-aryl-3,5-bis(arylethynyl)aryl-4H-1,2,4-triazoles derivatives is reported and the influence exerted by peripheral substitution on the morphology of the aggregates generated from these 1,2,4-triazoles is investigated by SEM imaging. The presence of paraffinic side chains results in long fibrillar supramolecular structures, but unsubstituted triazoles self-assemble into thinner ribbons and needle-like aggregates. The crystals obtained from methoxy-substituted triazoles have been utilised to elaborate a model that helps to justify aggregation of the investigated 1,2,4-triazoles, in which the operation of arrays of CH⋅⋅⋅π non-covalent interactions plays a significant role. The results presented herein demonstrate the ability of simple molecules to behave as multitasking scaffolds with different properties, depending on peripheral substitution. Thus, although 1,2,4-triazoles without long paraffinic side chains exhibit optical waveguiding behaviour, triazoles endowed with peripheral paraffinic side chains exhibit hexagonal columnar mesomorphism.

Influence of Polarity and Activation Energy in Microwave–Assisted Organic Synthesis (MAOS).

A. M. Rodríguez, P. Prieto, A. de la Hoz, A. Díaz-Ortiz, J. I. García.

ChemistryOpen, 2015, 4, 308-317

The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol⁻¹ and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation

Determination of kinetic parameters within a single non-isothermal on-flow experiment by Nanolitre-NMR spectroscopy

A.M. Rodríguez, A. de la Hoz, F. Jiménez-Márquez, R.M. Fratila, P.A. Berneveld, V. Gómez-Almagro, A. Velders

Analytical Chem. 2015, 87, 10547-10555.

Conventional methods to determine the kinetic parameters for a certain reaction require multiple, separate isothermal experiments, resulting in time- and material-consuming processes. Here, an approach to determine the kinetic information within a single nonisothermal on-flow experiment is presented, consuming less than 10 μmol of reagents and having a total measuring time of typically 10 min. This approach makes use of a microfluidic NMR chip hyphenated to a continuous-flow microreactor and is based on the capabilities of the NMR chip to analyze subnanomole quantities of material in the 25 nL detection volume. Importantly, useful data are acquired from the microreactor platform in specific isothermal and nonisothermal frames. A model fitting the experimental data enables rapid determination of kinetic parameters, as demonstrated for a library of isoxazole and pyrazole derivatives.

Solvent-Free Microwave-Assisted Synthesis of 2,5-Dimethoxyphenylaminotriazines

J. R. Ramírez, R. Caballero, J. Guerra, A. Ruiz-Carretero, A. Sánchez-Migallón, A. de la Hoz

ACS Sustainable Chem. Eng., 2015, 3 (12), pp 3405–3411

The green synthesis of asymmetric star-shaped 2,5-dimethoxyphenylamino-1,3,5-triazine derivatives using microwave irradiation in the absence of solvent is described. The title compounds have been characterized, and their properties as donor–acceptor (D–A) systems have been studied by UV–vis, fluorescence spectroscopy and electrochemical studies. The formation of excimers and the aggregation of these star-shaped triazine systems have been demonstrated.

Applications of metal-free 1,2,4-triazole derivatives in materials science.

A. Díaz-Ortiz, P. Prieto, J. R. Carrillo, R. Martín, I. Torres.

Curr. Org. Chem. 2015, 19, 568-584

The 1,2,4-triazole system has shown excellent electron-transport and hole-blocking properties owing to its highly electron-deficient nature. Accordingly, a large number of 1,2,4-triazole derivatives have been described as having a wide variety of uses in materials science. Triazoles are widely used in transition-metal complexes or metal-organic frameworks (MOFs), but metal-free 1,2,4-triazole derivatives have also exhibited interesting and useful properties as materials. The use of these derivatives, either as small molecules or polymers, in light-emitting devices has allowed the fabrication of OLEDs, PHOLEDs and PLEDs with excellent properties. Other materials have exhibited liquid crystalline or optical waveguide behavior or have found applications in PEMFCs, organic photovoltaic cells and data storage devices. The aim of this review is to discuss the most important metal-free derivatives bearing 1,2,4- triazole moieties with applications as organic materials.