A green chemistry procedure for a green chemistry catalyst

Título: A green chemistry procedure for a green chemistry catalyst
Subtítulo: A 3D-aromatic and photoredox catalyst, can be readily synthesized in high yield by a fast and clean solvent-free reaction. This innovative approach yields the desired molecules by simply heating the solid compounds to high temperature for a very short time

3,2,1 and stop! An innovative, straightforward and clean route for the flash synthesis of metallacarboranes
Ines Bennour, Ana M. Cioran, Francesc Teixidor, Clara Viñas
Green Chemistry 21, 1925, 2019
DOI: 10.1039/C8GC03943G

Figure: Schematic view of the valuable 3,2,1 and stop! synthetic procedure to achieve 3D shaped metallacarborane [Co(C2B9H11)2] derivatives.

As a target,Green Chemistry is the whole process aiming at producing chemical products that reduce or eliminate the use or generation of hazardous substances. Green chemistry goes beyond the synthesis and applies across the life cycle of a chemical product, including its use, and ultimate disposal.

By the judicious study of a desired compound, in our case a metallacarborane with a characteristic 3D shape, and with the formula [3,3’-Co(1,2-C2B9H11)2] has been possible by applying the concepts of green chemistry to create an alternative procedure to avoid hazardous substances. The process was designed to achieve the targeted metallacarborane at the shortest time while reducing waste and demand on energy.

In the paper cited below, a new, fast and environmentally-friendly solid state reaction for the syntheses of cobaltabis(dicarbollide) derivatives, [3,3’-Co(1,2-R2-1,2-C2B9H9)2] (R and R’= H, alkyl, aryl) is presented. Our approach is a significant improvement on the traditional syntheses in solution in both speed of reaction and generated yield. We demonstrate that the [3,3’-Co(1,2-C2B9H11)2] building reaction works well with starting plain, single or double Ccluster-substituted nido [7,8-C2B9H12]- clusters. However, care has to be taken when β-hydride elimination may take place because in this case the resulting [Co(C2B9H11)2] derivative may be different to the expected one based on the precursor nido cluster due to the β-hydride elimination, as commonly occurs in organometallic chemistry. The presence of substituents bearing a free pair of electrons also influences the complex formation. Meta-isomers also give rise to the corresponding cobaltabis(dicarbollide), [3,3’-Co(1,7-C2B9H11)2], but in this case, the reaction time needs to be increased. A suggested mechanism of the complexation reaction is proposed, based on identifying the chemical nature of the evolved gas, the pH of the mixture, the crystal structure of the target complex and the absence of Co2+ dismutation.

The fact that metallacarboranes can find many applications in materials, energy, catalysis, sensors/biosensors and medicine, among others makes this innovative, straightforward and clean route for their flash synthesis very valuable.

Ambipolar solution processed organic field-effect transistors (OFETs) and water-gated OFET with carbon-composite gate contact

Título: Ambipolar solution processed organic field-effect transistors (OFETs) and water-gated OFET with carbon-composite gate contact
Subtítulo: Unconventional solution processed organic field-effect transistors (OFETs): charge transfer complex as ambipolar semiconductor and carbon composite gate in electrolyte-gated OFET

Carbon-paste nanocomposites as unconventional gate electrodes for electrolyte-gated organic field-effect transistors: electrical modulation and bio-sensing
Jose Muñoz, Francesca Leonardi, Tayfun Özmen, Marta Riba-Moliner, Arantzazu González-Campo, Mireia Baeza, Marta Mas-Torrent
J. Mater. Chem. C 2019, 7, 14993
DOI: 10.1039/C9TC04929K

Solution-processed thin films of a charge transfer complex for ambipolar field-effect transistors
Tommaso Salzillo, Antonio Campos, Marta Mas-Torrent
J. Mater. Chem. C 2019, 7, 1025
DOI: 10.1039/C9TC03064F

Figure: (Left) Crystalline thin film of a charge transfer complex prepared from a solution of a donor and acceptor molecules blended with polystyrene as a binding polymer. (Right) Electrolyte-gated field-effect transistor in which the gate contact is a composite carbon based electrode composed of carbon-nanotubes functionalised with β-cyclodextrines.

Solution processed organic field-effect transistors (OFETs) are raising great interest for the development of low-cost electronics. Despite the impressive progress achieved in the last years, there is still plenty of room in terms of material engineering. Here, we highlight two recent works where we have used an unconventional material as active ambipolar semiconductor and another one where an alternative carbon-based electrode has been exploited as gate contact.

1) Charge transfer (CT) complexes are composed of a donor and acceptor molecule that crystallize together either in segregated or alternated stacks. They have been studied for a long time as organic conductors and, recently have also been attracting great interest as potential candidates for ambipolar semiconductors. However, their application in OFETs has been limited to ideal single crystals or to evaporated films, hindering their potential for real applications. Here, we report the preparation of thin films of a CT complex using a simple solution shearing technique and blending the precursors with a binding polymer. The resulting OFET devices exhibited ambipolar field-effect in environmental conditions. Thus, this work opens new perspectives for the application of CT complexes in electronic devices.

2) Nanocomposite paste electrodes using carbon nanotubes (CNTs) have been investigated for the first time in electrolyte-gated organic field-effect transistors (EGOFETs) as a replacement of conventional metal gate electrodes. The potential of using such non-conventional gate electrodes for sensing purposes has also been evaluated by investigating, as a proof of concept, the formation of a supramolecular complex between a CNT functionalised with β-cyclodextrin (β-CD) as a bio-recognition element and tryptophan, giving detection limits at picomolar levels. Accordingly, carbon-composite electrodes have been demonstrated to be a potential alternative to metal gate electrodes for the development of a new generation of highly sensitive carbon-based EGOFET bio-sensors.

Carboranes for the synthesis of innovative nanostructures

Título: Carboranes for the synthesis of innovative nanostructures

The Key to Controlling the Morphologies of Quantum Nanocrystals: Spherical Carborane Ligands
Abhishek Saini, Arpita Saha, Clara Viñas, Francesc Teixidor
Chem. Commun. 55, 9817-9820, 2019
DOI: 10.1039/c9cc03941d

Figure: Carboranes for the synthesis of innovative nanostructures application

Spherical boron ligands act as the pathway to achieve rare nanostructures in the Quantum regime, using a simple colloidal synthesis. Quantum Rings and Rods with intense photoluminescent properties can be synthesized in a single step synthesis, opening the door to bulk production of these fascinating nanomaterials, something never achieved before.

Carpet-like Graphene in polycristalline silicon carbide (SiC)

Título: Carpet-like Graphene in polycristalline silicon carbide (SiC)

Face dependent footprints of carpet-like graphene films grown on polycrystalline silicon carbide.
Cristina Ramírez, Eugenio García, Esther Barrena, Angel De Pablos, Manuel Belmonte, M. Isabel Osendi, Pilar Miranzo, Carmen Ocal
Carbon 153, 417-427, 2019
DOI: 10.1016/j.carbon.2019.07.031

Figure: Combination of different local probe and electron microscopies (SFM, KPFM,  RAMAN, FESEM images) as well as micro-Raman spectroscopy (purple spectrum) used to determine the dependence of the properties of graphene grown simultaneously on different facets of SiC.

The unique properties of graphene arise from its 2D structure but, in real applications, it cannot stand alone without a support. In this study, large-area, low-defect-density supported graphene is obtained by sublimation of silicon carbide (SiC). Employing polycrystalline SiC we compare graphene simultaneously grown on different facets at exactly the same conditions. We provide a reliable methodology to prepare continuous graphene on SiC components for scaling-up at low cost with controlled thickness, quality and stresses.

Flexible and lightweight organic molecular metal humidity sensor

Título: Flexible and lightweight organic molecular metal humidity sensor

On the Sensing Mechanisms of a Hydroresistive Flexible Film Based on an Organic Molecular Metal
Raphael Pfattner, Elena Laukhina, Laura Ferlauto, Fabiola Liscio, Silvia Milita, Anna Crespi, Victor Lebedev, Marta Mas-Torrent. Vladimir Laukhin, Concepció Rovira, Jaume Veciana
ACS Appl. Electron. Mater. 1, 9, 1781–1791, 2019
DOI: 10.1021/acsaelm.9b00322

Figure: Schematic illustration of reversible water uptake shown on top of SEM image taken from the cross section of a bilayer film. Insets: Electronic and structural phase transition of bilayer film with [(BEDT-TTF)5(Br4(H5O2))] as hydroresistive organic molecular metal.

We present the flexible bilayer film polycarbonate/polycrystalline organic molecular conductor as a promising material for humidity sensors which may be applied in a number of monitoring scenarios. The film is capable of monitoring air relative humidity levels from 15 up to 90 % as a well definite reproducible electrical signal.

Multifunctional molecular switches based on radical dendrimers.

Título: Multifunctional molecular switches based on radical dendrimers
Subtítulo: New radical dendrimers based on polyphosphorhydrazone (PPH) dendrimers fully functionalized with perchlorotriphenylmethyl (PTM) radicals as electrochemical molecular switches with optical (absorption and fluorescence) and magnetic responses.

Redox active PTM radical dendrimers as promising multifunctional molecular switches
Vega Lloveras, Flonja Liko, José L. Muñoz-Gómez, Jaume Veciana, José Vidal-Gancedo
Chem. Mater. 31, 22, 9400-9412, 2019
DOI: 10.1021/acs.chemmater.9b03015

Figure: Representation of the electrochemical switch (on/off) of PTM radical dendrimers (Gn(PTM·)x, n=0, 1, 2; x=6, 12, 24). The PTM molecule has two redox states, the radical (left) and anion (right) forms, which can be electrochemically interconverted. Radical dendrimers Gn(PTM·)x exhibit spin S=x.½ (EPR active), an absorbance band at 386 nm (yellow-brownish colour) and red fluorescence emission, and their corresponding anionic forms Gn(PTM-)x are diamagnetic species with S=0 (EPR silent), with a maximum absorbance band at ca. 520 nm (deep wine or purple colour) and are not fluorescent.

Nowadays, there is a great interest in using individual molecules as nanometer-scale switches and logic devices, with the aim of reaching higher power and smaller size. Demonstrating that one molecular switch can be turned on and off at room temperature, simply by applying a current to a neighboring molecule has interesting implications.

In this work, we report the synthesis and characterization of three generations of polyphosphorhydrazone (PPH) dendrimers, fully functionalized with 6, 12 and 24 redox active perchlorotriphenylmethyl (PTM) radicals in the periphery, capable of undergoing an electrochemical reversible switching (on/off) by multi-electron reduction and oxidation, for many cycles. An electrical input is used to trigger the physical properties of these radical dendrimers in a reversible way, modifying their optical and magnetic properties. Gn(PTM)x radical dendrimers are paramagnetic, exhibit an absorbance band at 386 nm and red fluorescence emission, if in radical state (on). When they are switched to their anion state, these dendrimers convert to diamagnetic species with a maximum absorbance band at ca. 520 nm and no fluorescence emission (off). Furthermore, in this work we open the perspective of controlling the exact number of electrons transferred during the switching process, that could lead not only to a two-state (on/off) but also to a multi-state switch in the near future.

In addition, the high electron accepting capacity of these radical dendrimers able to accept and donate up to 24 electrons per molecule at the same time at very accessible potentials and in a reversible way makes them good electron-reservoir molecules.

Undoubtedly, the high control over the synthesis, stability and reversibility of systems like the ones reported in this work, further supports the perspective of using macromolecules as scaffolds in the electronic devices of the future.

Organic free radicals: a new trend in optoelectronics and spintronics

Título: Organic free radicals: a new trend in optoelectronics and spintronics
Subtítulo: New perspectives in organic free radical molecules: when luminescence, chirality and magnetic activity result in a winning combination.

Organic Free Radicals as Circularly Polarized Luminescence Emitters
Paula Mayorga-Burrezo, Vicente G. Jiménez, Davide Blasi, Imma Ratera, Araceli G. Campaña, Jaume Veciana
Angew. Chem. Int. Ed. 58, 16282 –16288, 2019
DOI: 10.1002/anie.201909398

Figure: Molecular structures of optically and magnetically active enantiomers of one studied organic free radical

Over the past decades, increasing attention has been devoted to circularly polarized luminescence (CPL) up to becoming one of the most powerful and reliable spectroscopic tool for the analysis of a great variety of chemical systems. Resulting from the influence that chirality has over luminescent properties, the course of this technique is nowadays leaded by inorganic CPL emitters. However, it is known that pure organic samples with CPL activity may provide additional advantages (i.e. processability, lightness, transparency, etc.) and represent a hugely desirable option in several hot applications where toxicity factors are crucial (i.e., bioimaging). As a result, great efforts are currently being made for the development of these promising organic-based alternatives.

In this work, the study of CPL activity in organic free radicals emitters has been addressed for the first time, encouraged by the enhanced performance proved for magnetically active compounds in optics and optoelectronics. To this end, two triphenylmethyl (trityl) radical-based chlorinated derivatives, with propeller chirality, were considered, achieving an efficient chiral emission after the resolution of the racemic compounds.

Consequently, the pioneering approach here developed aims at laying the foundations for a new trend in optoelectronics and spintronics, where chiral, magnetic and luminescent properties can be used interchangeably in a single device. Thus, taking full advantage of the versatile nature of organic compounds will place us a step further in the miniaturization race of multifunctional nanomaterials.

Printed organic field-effect transistors using inks based on organic semiconducting molecules blended with insulating polymers

Título: Printed organic field-effect transistors using inks based on organic semiconducting molecules blended with insulating polymers
Subtítulo: The use of inks based on organic semiconducting molecules blended with insulating polymers results in large area crystalline films exhibiting high field-effect mobilities.

Organic semiconductor/polymer blend films for organic field-effect transistors
Sergi Riera-Galindo, Francesca Leonardi, Raphael Pfattner, Marta Mas-Torrent
Adv. Mater. Technol. 1900104, 2019
DOI: 10.1002/admt.201900104

Figure: Organic field-effect transistor based on a an organic semiconducting molecule/insulating polymer blended film.

The development of low‐cost organic electronics entails the processing of organic semiconductors employing solution‐based techniques in order to be able to print them at low temperature and on flexible substrates. Small conjugated semiconducting molecules can form highly ordered crystalline structures that give rise to high charge carrier mobilities. However, due to the low viscosity of their solutions, the preparation of large‐area uniform and reproducible films of these materials employing printing techniques can be very challenging. To circumvent this, a promising route is the use of blends of the organic semiconductors with insulating binding polymers. The resulting formulations are more viscous, facilitating the preparation of films covering large areas without facing dewetting issues and with high reproducibility.

Additionally, this approach typically gives rise to films with an enhanced crystallinity due to the vertical phase separation that takes place during the deposition, which works as a crystallisation process. Therefore, when the films are implemented in organic field‐effect transistor (OFETs), the devices exhibit a significantly improved performance in terms of mobility and stability. In this review paper, we describe the recent progress in the fabrication of OFETs based on inks of small semiconducting molecules with insulating polymers. Particular emphasis is placed on the morphology and structural characteristics of the films since they play a major role in determining the final electrical properties. Undoubtedly, the use of these types of blends results in more reliable and reproducible devices that can be fabricated on large areas and at low cost and, thus, this methodology brings great expectations for the implementation of organic semiconductors in real‐world applications.

Reversible switching of gold surface energy

Título: Reversible switching of gold surface energy
Subtítulo: Reversible switching of gold surface energy by near infrared irradiation using bistable Self Assembly Monolayers (SAMs) based on radical molecules

Effect of the Molecular Polarizability of SAMs on the Work Function Modification of Gold: Closed- versus Open-Shell Donor–Acceptor SAMs
Valentin Diez-Cabanes, Deyana Morales, Manuel Souto, Markos Paradinas, Francesca Delchiaro, Anna Painelli, Carmen Ocal, David Cornil, Jérôme Cornil, Jaume Veciana, Imma Ratera
Advanced Materials Technologies 4, 1800152, 2019
DOI: 10.1002/admt.201800152

Reversible switching of the Au(111) work function by near infrared irradiation with a bistable SAM based on a radical donor-acceptor dyad
Valentin Diez-Cabanes, Andrés Gomez, Manuel Souto, Nerea Gonzalez-Pato, Jérôme Cornil, Jaume Veciana, Imma Ratera
Journal of Materials Chemistry C 7, 7418, 2019
DOI: 10.1039/c9tc00906j

Figure: Reversible switching of gold WF by NIR irradiation using SAMs of D-A radicals.

In organic electronic devices, charge injection barriers at metal-organic interfaces can be tuned by modifying the work function (WF) of metallic electrodes using self-assembled monolayers (SAMs) of polar molecules. An interesting example of polar molecule is offered by donor–acceptor (D–A) dyads based on ferrocene (Fc) as electron-donor unit and a polychlorotriphenylmethyl radical as electron-acceptor unit, connected by a π-conjugated vinylene bridge. The magnitude of the shift in the charge injection barriers for this D–A systems is estimated by means of surface potential measurements performed by Kelvin probe force microscopy (KPFM). The experimental data has been rationalized by density functional theory calculations, which evidence the importance of presenting not only high molecular dipole moments but also low polarizabilities along the direction normal to the substrate to achieve high work function (WF) shifts of metals upon SAM formation.

Based on these findings, we have described the modification of the WF of Au(111) upon deposition of self-assembled monolayers (SAMs) of the two donor–acceptor (D–A) systems, the radical (Fc–PTM) dyad and its non-radical analogue. Interestingly, the WF of the radical SAM is significantly shifted by +250 when irradiated with NIR light recovering their original values when the irradiation is suppressed. This phenomena, is attributed to the bistable nature of this SAM in which neutral radical dyad molecules are excited into a zwitterionic state following a light driven intramolecular charge transfer (ICT) from the Fc unit to the PTM radical unit. Remarkable is the large WF shift attained, one of the highest values reported in the literature, and the unprecedented fact that it is achieved under irradiation in the IR region due to an intramolecular electronic reorganization. In contrast, the WF of the non-radical SAM does not change upon NIR irradiation since this SAM does not display bistability.

Substituents modulate the transport properties of chiral molecular conductors

Título: Substituents modulate the transport properties of chiral molecular conductors

Chiral EDT-TTF precursors with one stereogenic centre: substituent size modulation of the conducting properties in the (R-EDT-TTF)2PF6 (R = Me or Et) series
Nabil Mroweh, Pascale Auban-Senzier, Nicolas Vanthuyne, Enric Canadell, Narcís Avarvari
J. Mater. Chem C
7, 12664−12673, 2019
DOI: 10.1039/c9tc04243a

Figure: Depending on the R substituent in the (R-EDT-TTF) donor (center) two different conducting salts with 2:1 stoichiometry, [(R)-1]2PF6 (left) and  [(R)-2]2PF6 (right) can be prepared. The different donor layers lead to band formation with considerably different band width resulting with metals ([(R)-1]2PF6, left) or localized semiconductors ([(R)-2]2PF6, right).

Investigation of the influence of chirality on the transport properties requires the preparation of structurally different families of enantiopure conductors. Controlling the substituent bulkiness in the R-EDT-TTF donor leads, with the PF6 anion, to two different series of 2:1 enantiopure conducting salts with either metallic or activated conductivity.

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