Uthrene, a radically new molecule?

We have studied uthrene with a large range of quantum chemical models. Uthrene is predicted to be naturally twisted and to possess a triplet ground state, making it the smallest non-planar polycyclic biradical that can be derived from graphene.The present work was carried out with support by the Portuguese ‘‘Fundação para a Ciência e a Tecnologia’’ through the program Ciência 2008 and project scope UID/CEC/00319/2013, as well as with resources from the project SeARCH (Services and Advanced Research Computing with HTC/HPC clusters) funded under contract CONC-REEQ/ 443/2005. A visiting scholarship and computer time from the HPC-EUROPA2 project is also gratefully acknowledged.Fundação para a Ciência e a Tecnologia (FCT

QoS monitoring in real-time streaming overlays based on lock-free data structures

AbstractPeer-to-peer streaming is a well-known technology for the large-scale distribution of real-time audio/video contents. Delay requirements are very strict in interactive real-time scenarios (such as synchronous distance learning), where playback lag should be of the order of seconds. Playback continuity is another key aspect in these cases: in presence of peer churning and network congestion, a peer-to-peer overlay should quickly rearrange connections among receiving nodes to avoid freezing phenomena that may compromise audio/video understanding. For this reason, we designed a QoS monitoring algorithm that quickly detects broken or congested links: each receiving node is able to independently decide whether it should switch to a secondary sending node, called "fallback node". The architecture takes advantage of a multithreaded design based on lock-free data structures, which improve the performance by avoiding synchronization among threads. We will show the good responsiveness of the proposed approach on machines with different computational capabilities: measured times prove both departures of nodes and QoS degradations are promptly detected and clients can quickly restore a stream reception. According to PSNR and SSIM, two well-known full-reference video quality metrics, QoE remains acceptable on receiving nodes of our resilient overlay also in presence of swap procedures

Computer simulation of ionic solids of technological interest

In the present study we have applied Quantum Mechanical (QM) and Molecular Mechanics (MM) computational methods to solid state materials of interest, specifically: metal hydrides, olivines, ceria and tin oxide crystals. A new empirical potential set has been derived for the following metal hydrides; NaH, LiH, MgH2, CaH2 and BaH2. Studies of atomic diffusion have been performed in LiH and CaH2 and agree well with the available experimental data. MM simulations of cation diffusion in olivines have been performed. Diffusion has been found to come mainly from Mi-Mi nearest neighbour jumps with a smaller contribution by site exchange, MrM2 and M2-M1; jumps. The spatial exploration of non-linear diffusion paths has been shown crucial in order to yield correct estimations of the activation energy of diffusion. MM calculations of solution and clustering of Cu2+ in ceria show that, on the contrary to previous work, it is quite likely that the dopant enters in interstitials sites and, consequently all clusters observed experimentally may be formed by Cu2+ interstitials. QM cluster and periodic slab simulations have been performed on the CO and C02 adsorption on the (110) perfect surface of Sn02 with HF and DFT methods. These calculations show that, for CO, the molecule adsorbs on pentacoordinated cations on, ideal, truncated bulk, and relaxed surfaces. The interaction with the surface is mostly electrostatic and well described by uncorrelated methods. In the C02 case, the molecule adsorbs perpendicularly to the surface on the same site, but the main bonding contribution is the polarization of the C02 and DFT methods are necessary to properly describe the binding. Carbonates have been shown to be formed only as metastable species on the perfect (100) Sn02 surface

Planar and Helical Dinaphthophenazines

[EN] In this study, we report the synthesis of a series of planar and helical dinaphthophenazines by cyclocondensation reactions between the newly developed 9,10-bis((triisopropylsilyl)ethynyl)-anthracene-1,2-dione and different diamines. Their optoelectronic and electrochemical properties are studied by ultraviolet-visible (UV-vis) spectroscopy, fluorescence spectroscopy, cyclic voltammetry, and density functional theory calculations.A.M.-A. acknowledges support of the Basque Foundation for Science (Ikerbasque), POLYMAT, the University of the Basque Country, Diputacion Foral de Guipuzcoa, Gobierno Vasco (BERC programme) and Gobierno de Espana (Project CEX2020-001067-M financed by MCIN/AEI/10.13039/501100011033). Technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF) is acknowledged. This project received funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (grant agreement no. 722951). This project received funding from the European Union's Horizon 2020 Research and Innovation Programme under grant agreement nos. 664878 and 899895. F.C. and A.M.-A acknowledge that this project received funding from the European Union's Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie grant agreement no. 839626. M.M.-F. acknowledges support from the Portuguese Foundation for Science and Technology (FCT), under the project IF/00894/2015, and the project CICECO-Aveiro Institute of Materials, FCT ref UID/CTM/50011/2019, UIDB/50011/2020, and UIDP/50011/2020, financed by national funds through the FCT/MEC and when appropriate c-financed by FEDER under the PT2020 Partnership Agreement

Inducing Single-Handed Helicity in a Twisted Molecular Nanoribbon

[EN] Molecular conformation has an important role in chemistry and materials science. Molecular nanoribbons can adopt chiral twisted helical conformations. However, the synthesis of single-handed helically twisted molecular nanoribbons still represents a considerable challenge. Herein, we describe an asymmetric approach to induce single-handed helicity with an excellent degree of conformational discrimination. The chiral induction is the result of the chiral strain generated by fusing two oversized chiral rings and of the propagation of that strain along the nanoribbon's backbone.This work was carried out with support from the Basque Science Foundation for Science (Ikerbasque), POLYMAT, the University of the Basque Country, Gobierno Vasco (BERC Programme) and Gobierno de Espana (Ministerio de Ciencia e Innovacion, Plan Estatal de Investigacion Cientifica y Tecnica y de Innovacion). Technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF) is acknowledged. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement No. 722951). This project has received funding from the European Union's Horizon 2020 research and innovation programme under Grant Agreement No. 899895. In addition, support through the project IF/00894/2015, the advanced computing project CPCA/A2/2524/2020 granting access to the Navigator cluster at LCA-UC and within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 and UIDP/50011/2020 funded by national funds through the Portuguese Foundation for Science and Technology I.P./MCTES is gratefully acknowledged

Doubling the Length of the Longest Pyrene-Pyrazinoquinoxaline Molecular Nanoribbons

[EN] Molecular nanoribbons are a class of atomically-precise nanomaterials for a broad range of applications. An iterative approach that allows doubling the length of the longest pyrene-pyrazinoquinoxaline molecular nanoribbons is described. The largest nanoribbon obtained through this approach-with a 60 linearly-fused ring backbone (14.9 nm) and a 324-atoms core (C276N48)-shows an extremely high molar absorptivity (values up to 1 198 074 M-1 cm(-1)) that also endows it with a high molar fluorescence brightness (8700 M-1 cm(-1)).This work was carried out with support from the Basque Science Foundation for Science (Ikerbasque), POLYMAT, the University of the Basque Country, Diputacion de Guipuzcoa, Gobierno Vasco (BERC programme) and Gobierno de Espana (Project CEX2020-001067-M financed by MCIN/AEI/10.13039/501100011033). Technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF) is acknowledged. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement No. 722951). This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 899895. In addition, support through the project IF/00894/2015, the advanced computing project CPCA/A2/2524/2020 granting access to the Navigator cluster at LCA-UC and within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020 funded by national funds through the Portuguese Foundation for Science and Technology I.P./MCTES is gratefully acknowledged

Diameter selective characterization of single-wall carbon nanotubes

A novel method is presented which allows the characterization of diameter selective phenomena in SWCNTs. It is based on the transformation of fullerene peapod materials into double-wall carbon nanotubes and studying the diameter distribution of the latter. The method is demonstrated for the diameter selective healing of nanotube defects and yield from C$_{70}$ peapod samples. Openings on small diameter nanotubes are closed first. The yield of very small diameter inner nanotubes from C$_{70}$ peapods is demonstrated. This challenges the theoretical models of inner nanotube formation. An anomalous absence of mid-diameter inner tubes is observed and explained by the suppressed amount of C$_{70}$ peapods due to the competition of the two almost equally stable standing and lying C$_{70}$ peapod configurations

Modulating Strain in Twisted Pyrene-Fused Azaacenes

The design and synthesis of strained aromatics provide an additional insight into the relationship between structure and properties. In the last years, several approaches to twist pyrene-fused azaacenes have been developed that allow to introduce twists of different sizes. Herein, we describe the synthesis of a new set of twisted dibenzotetraazahexacenes constituted by fused pyrene and quinoxaline residues that have been distorted by introducing increasingly larger substituents on the quinoxaline residues. Their twisted structure has been demonstrated by single-crystal X-ray diffraction. Furthermore, absorption, fluorescence, electrochemical and theoretical studies shine light on the effects of the substituents and twists on the optoelectronic and redox properties.This work was carried out with support from the Basque Science Foundation for Science (Ikerbasque), POLYMAT, the University of the Basque Country, Diputación de Guipúzcoa, Gobierno Vasco (PIBA_2022_1_0031 and BERC programme) and Gobierno de España (Projects PID2021-124484OB-I00 and CEX2020-001067-M financed by MCIN/AEI/10.13039/501100011033). Project (PCI2022-132921) funded by the Agencia Estatal de Investigación through the PCI 2022 and M-ERA.NET 2021 calls. This project has received funding from the European Research Council (ERC) under the European Union's Horizon2020 research and innovation programme (Grant Agreement No. 722951). This work was funded by the European Union under the Horizon Europe grant 101046231. Technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF) is acknowledged. In addition, support through the project IF/00894/2015, the advanced computing project 2021.09622.CPCA granting access to the Navigator cluster at LCA-UC, and within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC) is gratefully acknowledged

Microencapsulation of herbicide MCPA with native β-cyclodextrin and its methyl and hydroxypropyl derivatives : an experimental and theoretical investigation

When a pesticide is released into the environment, most of it is lost before it reaches its target. An effective way to reduce environmental losses of pesticides is by using controlled release technology. Microencapsulation becomes a promising technique for the production of controlled release agricultural formulations. In this work, the microencapsulation of chlorophenoxy herbicide MCPA with native β-cyclodextrin and its methyl and hydroxypropyl derivatives was investigated. The phase solubility study showed that both native and β-CD derivatives increased the water solubility of the herbicide and inclusion complexes are formed in a stoichiometric ratio of 1:1. The stability constants describing the extent of formation of the complexes have been determined by phase solubility studies. 1H NMR experiments were also accomplished for the prepared solid systems and the data gathered confirm the formation of the inclusion complexes. 1H NMR data obtained for the MCPA/CDs complexes disclosed noticeable proton shift displacements for OCH2 group and H6 aromatic proton of MCPA provided clear evidence of inclusion complexation process, suggesting that the phenyl moiety of the herbicide was included in the hydrophobic cavity of CDs. Free energy molecular mechanics calculations confirm all these findings. The gathered results can be regarded as an essential step to the development of controlled release agricultural formulations containing herbicide MCPA.Fundação para a Ciência e a Tecnologia (FCT

A Thiadiazole-capped Nanoribbon with 18 Linearly-Fused Rings

Polycyclic aromatic hydrocarbons that extend over 2 nm in one dimension are seen as monodisperse graphene nanoribbons, which have attracted significant attention for a broad range of applications in organic electronics and photonics. Herein we report the synthesis of a stable bisthiadiazole-capped pyrene-containing nanoribbon with 18 linearly fused rings (NR-18-TD). Thanks to the presence of alternating tert-butyl and tri-iso-butylsilyl groups, NR-18-TD is highly soluble in organic solvents and therefore its structure and fundamental optoelectronic, redox and electrical properties could be unambiguously established. This work illustrates that NR-18-TD is a promising soluble NR-based n-type semiconductor for applications in organic electronics.The authors are grateful to the Basque Science Foundation for Science (Ikerbasque), POLYMAT, the University of the Basque Country (Grupo de Investigación GIU17/054 and SGIker), Gobierno de España (Ministerio de Economía y Competitividad CTQ2016-77970-R and CTQ2015-71936-REDT), Gobierno Vasco (BERC program), CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013), Diputación Foral de Guipúzcoa (OF215/2016(ES)) and the FP7 framework program of the European Union (Marie Curie Career Integration Grant No. 618247 (NIRVANA)). This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 664878. This project has also received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 722951