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11.
Single‐Walled Carbon Nanotubes in Highly Viscous Media: A Comparison between the Dispersive Agents [BMIM][BF4], L121, and Triton X‐100 下载免费PDF全文
Dr. Carla Gasbarri Prof. Fausto Croce Dr. Ida Meschini Christopher H. Bowen Dr. Lisa Marinelli Prof. Antonio Di Stefano Dr. Guido Angelini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(2):546-549
Dispersions of single‐walled carbon nanotubes (SWNTs) have been prepared by using the room‐temperature ionic liquid [BMIM][BF4] (1‐butyl‐3‐methylimidazolium tetrafluoroborate), the triblock copolymer Pluronic L121 [poly(ethylene oxide)5‐poly(propylene oxide)68‐poly(ethylene oxide)5] and the non‐ionic surfactant Triton X‐100 (TX100) in the pure state. The size of the SWNTs aggregates and the dispersion degree in the three viscous systems depend on the sonication time, as highlighted by UV/Vis/NIR spectroscopy and optical microscopy analysis. A nonlinear increase in conductivity can be observed as a function of the SWNTs loading, as suggested by electrochemical impedance spectroscopy. The generation of a three‐dimensional network of SWNTs showing a viscoelastic gel‐like behavior above a critical percolation concentration has been found at 25 °C in all the investigated systems by oscillatory rheology measurements. 相似文献
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High‐Energy Long‐Lived Mixed Frenkel–Charge‐Transfer Excitons: From Double Stranded (AT)n to Natural DNA 下载免费PDF全文
Dr. Ignacio Vayá Dr. Johanna Brazard Dr. Miquel Huix‐Rotllant Dr. Arun K. Thazhathveetil Prof. Frederick D. Lewis Dr. Thomas Gustavsson Prof. Dr. Irene Burghardt Dr. Roberto Improta Dr. Dimitra Markovitsi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(14):4904-4914
The electronic excited states populated upon absorption of UV photons by DNA are extensively studied in relation to the UV‐induced damage to the genetic code. Here, we report a new unexpected relaxation pathway in adenine–thymine double‐stranded structures (AT)n. Fluorescence measurements on (AT)n hairpins (six and ten base pairs) and duplexes (20 and 2000 base pairs) reveal the existence of an emission band peaking at approximately 320 nm and decaying on the nanosecond time scale. Time‐dependent (TD)‐DFT calculations, performed for two base pairs and exploring various relaxation pathways, allow the assignment of this emission band to excited states resulting from mixing between Frenkel excitons and adenine‐to‐thymine charge‐transfer states. Emission from such high‐energy long‐lived mixed (HELM) states is in agreement with their fluorescence anisotropy (0.03), which is lower than that expected for π–π* states (≥0.1). An increase in the size of the system quenches π–π* fluorescence while enhancing HELM fluorescence. The latter process varies linearly with the hypochromism of the absorption spectra, both depending on the coupling between π–π* and charge‐transfer states. Subsequently, we identify the common features between the HELM states of (AT)n structures with those reported previously for alternating (GC)n: high emission energy, low fluorescence anisotropy, nanosecond lifetimes, and sensitivity to conformational disorder. These features are also detected for calf thymus DNA in which HELM states could evolve toward reactive π–π* states, giving rise to delayed fluorescence. 相似文献
16.
Santos Alexandre F. Aguado Roberto Corazza Marcos L. Tarrs Quim Sanchez-Salvador Jose-Luis Blanco Angeles Negro Carlos Delgado-Aguilar Marc 《Cellulose (London, England)》2022,29(10):5609-5622
Cellulose - In this work a wide sample analysis, under similar conditions, has been carried out and a calibration strategy based on a careful selection of input variables combined with sensitivity... 相似文献
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María Elena Snchez-Vergara Citlalli Rios Omar Jimnez-Sandoval Roberto Salcedo 《Molecules (Basel, Switzerland)》2020,25(24)
The structure formed by cobalt phthalocyanine (CoPc) and cobalt octaethylporphyrin (CoOEP) with electron-acceptor tetracyano-π-quinodimethane (TCNQ), was studied by Density Functional Theory (DFT) methods. According to theoretical calculations, both cobalt systems can establish dispersion forces related to TCNQ and also in both cases the link between them is built by means of hydrogen bonds. Based on the results of these DFT calculations, we developed experimental work: the organic semiconductors were doped, and the thermal evaporation technique was used to prepare semiconductor thin films of such compounds. The structure of the films was studied by FTIR and Raman spectroscopy. The optical properties of the CoPc-TCNQ and CoOEP-TCNQ films were investigated by means of UV-Vis measurements. The results obtained were used to estimate the type of transitions and the optical bandgap. The results were compared to the previously calculated theoretical bandgap. The CoOEP-TCNQ film presented the smallest theoretical and experimental bandgap. Finally, the electrical properties of the organic semiconductors were evaluated from a PET (polyethylene terephthalate)/indium tin oxide (ITO)/cobalt macrocycle-TCNQ/silver (Ag) device we prepared. The CoOEP-TCNQ-based device showed an ohmic behavior. The device manufactured from CoPc-TCNQ also showed an ohmic behavior at low voltages, but significantly changed to SCLC (space-charge limited conductivity) at high voltage values. 相似文献
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Carlos Raimundo Andrade Lima Jefferson da Silva Martins Caroline Pinheiro Luis Fernando de Avila Roberto Rosas Pinho Maria Luiza Miranda Rocco Wilson de Souza Melo Fabio Zappa 《Journal of Polymer Science.Polymer Physics》2019,57(15):967-972
Photopolymerization is a phenomenon that is the basis of much of today's microfabrication technology and intense research is conducted to improve its control and the characteristics of end products for a variety of applications. The design of microscopic structures often relies on the accurate knowledge and modeling of photopolymer's behavior upon exposure, i.e. the Dill parameters, for each radiation species of interest and therefore the development of flexible characterization techniques is of great importance. SU‐8 is a popular compound that is representative of a whole class that relies on cationic polymerization, where an acid is obtained via photolysis of an onium salt during exposure. Here we report on the observation of SbF6? via laser desorption mass spectrometry on SU‐8 exposed to UV light at the wavelength of 365 nm and demonstrate that the yield of this counter‐anion as a function of exposure is consistent with the Dill C parameter value available in the literature. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 967–972 相似文献
19.
Saulius Kaciulis Alessio Mezzi Roberto Montanari Maria Richetta Ekaterina Pakhomova Alessandra Varone 《Surface and interface analysis : SIA》2020,52(12):1093-1097
The W-1%La2O3 alloy has been irradiated by a single laser pulse (λ = 1064 nm) to simulate transient thermal loads of high energy occurring in a tokamak under operative conditions. A zone with a diameter of ~2 mm, namely, much larger than the focal spot, results to be affected by the pulse, and a crater of about 300 μm is observed in its center. La2O3 particles are not present inside the crater. The change of surface morphology is accompanied by elemental redistribution. Multipoint XPS analysis evidenced that the concentration of La is very low in the crater and increases moving toward the border of the affected zone while that of W shows an opposite trend. The composition changes involve only the outmost 5 nm of the sample: through depth profiling, no differences of chemical composition were detected deeper in the alloy between the center and external border of the affected area. 相似文献
20.
Dr. Ignacio Colomer Dr. Mercedes Ureña Dr. Alma Viso Prof. Roberto Fernández de la Pradilla 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(20):4620-4632
The chemo- and stereocontrolled functionalization of conjugated sulfinyl dienes in a cascade process that involves a conjugate addition, diastereoselective protonation and a [2,3]-sigmatropic rearrangement is reported. Enantioenriched 1,4-diol and 1,4-aminoalcohol derivatives are obtained in a very straightforward manner. Further functionalization of these structures, including highly stereoselective epoxidation, dihydroxylation and the stereodivergent synthesis of several polyols in a controlled fashion is described. 相似文献