Robust Amide-Linked Fluorinated Covalent Organic Framework for Long-Term Oxygen Reduction Reaction Electrocatalysis.

The high energy demand of the evolving world opens the door to develop more sustainable and environmentally friendly energy sources. Oxygen reduction reaction (ORR) is a promising candidate, being the 2e- pathway of great interest for the green production of hydrogen peroxide. Metal-free covalent organic frameworks (COFs) electrocatalysts present a suitable alternative to substitute the noble-metals more commonly employed in this application. However, the lability of the linkages building up the framework raises an issue for their long-term use and application in aggressive media. Herein, a stable amide-linked COF is reported through post-synthetic modification of a previously reported imine-linked COF proven to be effective as an electrocatalyst, enhancing its chemical stability and electrochemical response. It is found that after the linkage transformation, the new electrocatalyst displays a higher selectivity toward the H2O2 production (98.5%) and an enhanced turnover frequency of 0.155 s-1, which is among the bests reported to date for metal-free and COF based electrocatalysts. The results represent a promising step forward for metal-free non pyrolyzed electrocatalysts, improving their properties through post-synthetic linkage modification for long-term operation.

Turn-On Solid-State Fluorescent Determination of Zinc Ion by Quinoline-Based Covalent Organic Framework.

A new quinoline-based COF (covalent organic framework), obtained by Povarov reaction, containing 2,6-diisopropylphenyl moieties as substituents over the heterocyclic ring is described for detecting Zn2+ in aqueous solution. The introduction of the mentioned bulky phenyl rings into the network favors an increase of the distance between the reticular sheets and their arrangement, obtaining a new material with an alternating AB type stacking. The new material exhibits good selectivity to detect Zn2+ by fluorescence emission in aqueous solutions up to a concentration of 1.2 × 10-4 m of the metal ion. In order to have a deeper insight into the interaction between the COF and the zinc cation, a thorough spectroscopical, microscopical, and theoretical study is also presented and discussed in this communication.

V-Shaped Tröger Oligothiophenes Boost Triplet Formation by CT Mediation and Symmetry Breaking.

A new family of molecules obtained by coupling Tröger's base unit with dicyanovinylene-terminated oligothiophenes of different lengths has been synthesized and characterized by steady-state stationary and transient time-resolved spectroscopies. Quantum chemical calculations allow us to interpret and recognize the properties of the stationary excited states as well as the time-dependent mechanisms of singlet-to-triplet coupling. The presence of the diazocine unit in Tröger's base derivatives is key to efficiently producing singlet-to-triplet intersystem crossing mediated by the role of the nitrogen atoms and of the almost orthogonal disposition of the two thiophene arms. Spin-orbit coupling-mediated interstate intersystem crossing (ISC) is activated by a symmetry-breaking process in the first singlet excited state with partial charge transfer character. This mechanism is a characteristic of these molecular triads since the independent dicyanovinylene-oligothiophene branches do not display appreciable ISC. These results show how Tröger's base coupling of organic chromophores can be used to improve the ISC efficiency and tune their photophysics.

Scalable Synthesis and Electrocatalytic Performance of Highly Fluorinated Covalent Organic Frameworks for Oxygen Reduction.

In this study, we present a novel approach for the synthesis of covalent organic frameworks (COFs) that overcomes the common limitations of non-scalable solvothermal procedures. Our method allows for the room-temperature and scalable synthesis of a highly fluorinated DFTAPB-TFTA-COF, which exhibits intrinsic hydrophobicity. We used DFT-based calculations to elucidate the role of the fluorine atoms in enhancing the crystallinity of the material through corrugation effects, resulting in maximized interlayer interactions, as disclosed both from PXRD structural resolution and theoretical simulations. We further investigated the electrocatalytic properties of this material towards the oxygen reduction reaction (ORR). Our results show that the fluorinated COF produces hydrogen peroxide selectively with low overpotential (0.062 V) and high turnover frequency (0.0757 s-1 ) without the addition of any conductive additives. These values are among the best reported for non-pyrolyzed and metal-free electrocatalysts. Finally, we employed DFT-based calculations to analyse the reaction mechanism, highlighting the crucial role of the fluorine atom in the active site assembly. Our findings shed light on the potential of fluorinated COFs as promising electrocatalysts for the ORR, as well as their potential applications in other fields.

An international consortium in epilepsy surgery education: Clinical case-based discussions between Latin-American and Canadian Epilepsy Centers.

An international consortium with a focus on Epilepsy Surgery Education was established with members from different centers in Latin America and Canada. All members of the consortium and attendees from different centers in Latin America and Canada have been meeting to discuss epilepsy surgery cases in a virtual manner. We surveyed all to assess the value of the meetings. The results and description of these meetings are being presented.

Electrochemical (Bio)Sensors Based on Covalent Organic Frameworks (COFs).

Covalent organic frameworks (COFs) are defined as crystalline organic polymers with programmable topological architectures using properly predesigned building blocks precursors. Since the development of the first COF in 2005, many works are emerging using this kind of material for different applications, such as the development of electrochemical sensors and biosensors. COF shows superb characteristics, such as tuneable pore size and structure, permanent porosity, high surface area, thermal stability, and low density. Apart from these special properties, COF's electrochemical behaviour can be modulated using electroactive building blocks. Furthermore, the great variety of functional groups that can be inserted in their structures makes them interesting materials to be conjugated with biological recognition elements, such as antibodies, enzymes, DNA probe, aptamer, etc. Moreover, the possibility of linking them with other special nanomaterials opens a wide range of possibilities to develop new electrochemical sensors and biosensors.

Retinal Ganglion Cell Loss and Microglial Activation in a SOD1G93A Mouse Model of Amyotrophic Lateral Sclerosis.

The neurodegenerative disease amyotrophic lateral sclerosis (ALS) affects the spinal cord, brain stem, and cerebral cortex. In this pathology, both neurons and glial cells are affected. However, few studies have analyzed retinal microglia in ALS models. In this study, we quantified the signs of microglial activation and the number of retinal ganglion cells (RGCs) in an SOD1G93A transgenic mouse model at 120 days (advanced stage of the disease) in retinal whole-mounts. For SOD1G93A animals (compared to the wild-type), we found, in microglial cells, (i) a significant increase in the area occupied by each microglial cell in the total area of the retina; (ii) a significant increase in the arbor area in the outer plexiform layer (OPL) inferior sector; (iii) the presence of cells with retracted processes; (iv) areas of cell groupings in some sectors; (v) no significant increase in the number of microglial cells; (vi) the expression of IFN-γ and IL-1ß; and (vii) the non-expression of IL-10 and arginase-I. For the RGCs, we found a decrease in their number. In conclusion, in the SOD1G93A model (at 120 days), retinal microglial activation occurred, taking a pro-inflammatory phenotype M1, which affected the OPL and inner retinal layers and could be related to RGC loss.

Molecular characterization of Spanish patients with MECP2 duplication syndrome.

MECP2 duplication syndrome (MDS) is an X-linked neurodevelopmental disorder characterized by a severe to profound intellectual disability, early onset hypotonia and diverse psycho-motor and behavioural features. To date, fewer than 200 cases have been published. We report the clinical and molecular characterization of a Spanish MDS cohort that included 19 boys and 2 girls. Clinical suspicions were confirmed by array comparative genomic hybridization and multiplex ligation-dependent probe amplification (MLPA). Using, a custom in-house MLPA assay, we performed a thorough study of the minimal duplicated region, from which we concluded a complete duplication of both MECP2 and IRAK1 was necessary for a correct MDS diagnosis, as patients with partial MECP2 duplications lacked some typical clinical traits present in other MDS patients. In addition, the duplication location may be related to phenotypic severity. This observation may provide a new approach for genotype-phenotype correlations, and thus more personalized genetic counselling.

Gas-Solid Heterogeneous Postsynthetic Modification of Imine-Based Covalent Organic Frameworks.

The copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction is among the most extensively used strategies for the post-polymerization modification of COFs. This work shows a new procedure for the postsynthetic functionalization of imine-based COFs by using a heterogeneous solid-gas reaction between alkyne-functionalized COFs and azides in the absence of a copper catalyst. This new alternative represents a step forward towards a greener postsynthetic modification of COFs opening a high potential for the development of new applications.

Post-synthetic modification of covalent organic frameworks.

Covalent organic frameworks (COFs) are organic porous materials with many potential applications, which very often depend on the presence of chemical functionality at the organic building blocks. Functionality that cannot be introduced into COFs directly via de novo syntheses can be accessed through post-synthetic modification (PSM) strategies. Current strategies for the post-synthetic modification of COFs involve (i) incorporation of a variety of active metal species by using metal complexation through coordination chemistry, (ii) covalent bond formation between existing pendant groups and incoming constituents and (iii) chemical conversion of linkages. (iv) The post-synthetic modification is sometimes assisted by a monomer truncation strategy for the internal functionalization of COFs. (v) Even more intriguing methods that go beyond PSM are herein termed building block exchange (BBE) which encompasses framework-to-framework transformations taking advantage of the fact that reversible bond formation is a characteristic feature of COFs. This strategy allows the use of protoCOF structures (i.e., the utilization of a parent COF as a template) for the evolution of new COF structures with completely new components.

Synergistic Effect of Covalent Bonding and Physical Encapsulation of Sulfur in the Pores of a Microporous COF to Improve Cycling Performance in Li-S Batteries.

Lithium-sulfur batteries stands out as a promising technology for energy storage owing to a combination of favorable characteristics including a high theoretical gravimetric capacity, energy density, inexpensive character, and environmental benignity. Covalent organic frameworks (COFs) are a rapidly developing family of functional nanostructures which combine porosity and crystallinity, and which have been already used in these kinds of batteries to build sulfur electrodes, by embedding sulfur into porous COFs in order to enhance cycle lifetimes. In this contribution, this is taken one step forward and a COF endowed with vinyl groups is used, in order to graft sulfur to the COF skeleton through inverse vulcanization. The main aim of the article is to show the synergistic effect of covalent bonding and physical encapsulation of sulfur in the pores of the COF in order to alleviate the fatal redox shuttling process, to improve the cycling performance, and to provide faster ion diffusion pathways. In addition, it is shown how the material with covalently-bound S provides better electrochemical performance under demanding and/or changeable charge conditions than a parent analogue material with sulfur physically confined, but without covalent linkage.

Covalent organic frameworks based on Schiff-base chemistry: synthesis, properties and potential applications.

Covalent organic-frameworks (COFs) are an emerging class of porous and ordered materials formed by condensation reactions of organic molecules. Recently, the Schiff-base chemistry or dynamic imine-chemistry has been widely explored for the synthesis of COFs. The main reason for this new tendency is based on their high chemical stability, porosity and crystallinity in comparison to previously reported COFs. This critical review article summarizes the current state-of-the-art on the design principles and synthetic strategies toward COFs based on Schiff-base chemistry, collects and rationalizes their physicochemical properties, as well as aims to provide perspectives of potential applications which are at the forefront of research in materials science.

Tuning of the Electronic Levels of Oligothiophene-Naphthalimide Assemblies by Chemical Modification.

Inversion of the connections of amidine linkers combined with controlled oligothiophene chain catenation in oligothiophene-naphthalimide assemblies provides an efficient method to tune the HOMO and LUMO values in this type of assemblies. This modification also suppresses the intramolecular charge transfer (ICT) band normally found in this type of derivatives, also delocalizing the frontier molecular orbitals over the whole conjugated skeleton. The resultant assemblies were used in the fabrication of field-effect transistors, which showed well-balanced ambipolar transport.

Benzotrithiophene versus Benzo/Naphthodithiophene Building Blocks: The Effect of Star-Shaped versus Linear Conjugation on Their Electronic Structures.

The synthesis, characterization, and optical properties of a novel star-shaped oligothiophene with a central rigid trithienobenzene (BTT) core and diketopyrrolopyrrole (DPP) units are reported and compared with homologous linear systems based on the benzodithiophene (BDT) and the naphthodithiophene (NDT) units end capped with DPPs. This comparison is aimed at elucidating the effect of the star-shaped configuration versus linear conformation on the optical and electrical properties. Electronic and vibrational spectroscopies, together with transient absorption spectroscopy, scanning electronic microscopy, and DFT calculations are used to understand not only the molecular properties of these semiconductors, but also to analyze the supramolecular aggregation in these derivatives. We conclude that although the subject star-shaped derivative is not optimal in terms of π-conjugation, its extended BTT unit significantly favors intermolecular π-stacking interactions, which is interesting for their applications in devices. Field-effect transistors and solar cells were fabricated with these new molecular semiconductors and the performance difference discussed.

Synthesis of Perylene Imide Diones as Platforms for the Development of Pyrazine Based Organic Semiconductors.

There is a great interest in peryleneimide (PI)-containing compounds given their unique combination of good electron accepting ability, high abosorption in the visible region, and outstanding chemical, thermal, and photochemical stabilities. Thus, herein we report the synthesis of perylene imide derivatives endowed with a 1,2-diketone functionality (PIDs) as efficient intermediates to easily access peryleneimide (PI)-containing organic semiconductors with enhanced absorption cross-section for the design of tunable semiconductor organic materials. Three processable organic molecular semiconductors containing thiophene and terthiophene moieties, PITa, PITb, and PITT, have been prepared from the novel PIDs. The tendency of these semiconductors for molecular aggregation have been investigated by NMR spectroscopy and supported by quantum chemical calculations. 2D NMR experiments and theoretical calculations point to an antiparallel π-stacking interaction as the most stable conformation in the aggregates. Investigation of the optical and electrochemical properties of the materials is also reported and analyzed in combination with DFT calculations. Although the derivatives presented here show modest electron mobilities of ∼10-4 cm2V-1s-1, these preliminary studies of their performance in organic field effect transistors (OFETs) indicate the potential of these new building blocks as n-type semiconductors.

Hexaazatriphenylene (HAT) derivatives: from synthesis to molecular design, self-organization and device applications.

Dipyrazino[2,3-f:2',3'-h]quinoxaline also known as 1,4,5,8,9,12-hexaazatriphenylene (HAT) is an electron deficient, rigid, planar, aromatic discotic system with an excellent π­π stacking ability. Because it is one of the smallest two-dimensional N-containing polyheterocyclic aromatic systems, it has been used as the basic scaffold for larger 2D N-substituted polyheterocyclic aromatics. Furthermore, it is the building block of choice in a plethora of molecular, macromolecular and supramolecular systems for a variety of applications. This review is aimed to critically review the research performed during the almost three decades of research based on HAT from the synthetic, theoretical and application points of view. The design principles and synthetic strategies towards HAT derivatives will be established and their use in n-type semiconductors, sensors, nonlinear optical chromophores, liquid crystals, microporous polymers for energy storage and nano and microstructures will reveal the relevance of HAT as a basic scaffold in the areas of organic materials and nanoscience.

Exploring Advanced Oxygen Reduction Reaction Electrocatalysts: The Potential of Metal-Free and Non-Pyrolyzed Covalent Organic Frameworks.

Oxygen reduction reaction (ORR) electrocatalysis is an area of increasing interest for the in-situ production of H2O2 or the development of energy-related devices such as hydrogen fuel cells. Although pyrolyzed catalysts still offer the best performances to date with reference to the organic-based catalysts, metal-free and non-pyrolyzed covalent organic frameworks (COFs) stands out as promising alternatives candidates due to their favourable characteristics such as crystallinity, porosity, and organic composition, allowing the study of structural-property relationships. Herein, we present the design principles and recent advances in COFs-based ORR electrocatalysts, demonstrating how composition influences the activity and electronic pathway of the oxygen reduction process.

Molecular and electronic-structure basis of the ambipolar behavior of naphthalimide-terthiophene derivatives: implementation in organic field-effect transistors.

A new family of naphthalimide-fused thienopyrazine derivatives for ambipolar charge transport in organic field-effect transistors is presented. Their electronic and molecular structures were elucidated through optical and vibrational spectroscopy aided by DFT calculations. The results indicate that these compounds have completely planar molecular skeletons which promote good film crystallinity and low reorganization energies for both electron and hole transport. Their performance in organic field-effect transistors is compared with twisted and planar naphthaleneamidine monoimide-fused terthiophenes in order to understand the origin of ambipolarity in this new series of molecular semiconductors.

Rational design of ambipolar organic semiconductors: is core planarity central to ambipolarity in thiophene-naphthalene semiconductors?

Herein, we report a new family of naphthaleneamidinemonoimide-fused oligothiophene semiconductors designed for facile charge transport in organic field-effect transistors (OFETs). These molecules have planar skeletons that induce high degrees of crystallinity and hence good charge-transport properties. By modulating the length of the oligothiophene fragment, the majority carrier charge transport can be switched from n-type to ambipolar behavior. The highest FET performance is achieved for solution-processed films of 10-[(2,2'-bithiophen)-5-yl]-2-octylbenzo[lmn]thieno[3',4':4,5]imidazo[2,1-b][3,8]phenanthroline-1,3,6(2H)-trione (NDI-3 Tp), with optimized film mobilities of 2×10(-2) and 0.7×10(-2) cm(2) V(-1) s(-1) for electrons and holes, respectively. Finally, these planar semiconductors are compared with their twisted-skeleton counterparts, which exhibit only n-type mobility, in order to understand the origin of the ambipolarity in this new series of molecular semiconductors.

Graphene functionalisation with a conjugated poly(fluorene) by click coupling: striking electronic properties in solution.

Graphene flakes covalently modified with a conjugated polymer, poly[(9,9-dihexylfluorene)-co-alt-(9,9-bis-(6-azidohexyl)fluorene)] (PFA), were efficiently synthesised by a Cu-catalysed Huisgen 1,3-dipolar cycloaddition between alkyne-modified graphene and an azide-functionalised polymer. Two approaches for the modification of graphene with alkyne groups were investigated (coupling with a diazonium salt generated in situ or an amidation reaction) and the optimum conditions determined. The success of the click-coupling approach was confirmed by FTIR, (1)H NMR, Raman, and X-ray photoelectron spectroscopy (XPS). The absorption and emission spectra of the click product show a strong solvent dependency.