Mechanistic and Kinetic Study on the Reactions of Coumaric Acids with Reactive Oxygen Species: A DFT Approach

The mechanism and kinetics of reactions between coumaric acids and a series of reactive oxygen species (^•OX) was studied through the density functional theory (DFT). H atom abstraction from −OH and −COOH groups and addition to the nonaromatic double bond were the most representative reaction pathways chosen for which free energy barriers and rate constants were calculated within the transition state theory (TST) framework. From these calculations, it was estimated that ^•OH > ^•OCH₃ > ^•OOH > ^•OOCH₃ is the order of reactivity of ^•OX with any coumaric acid. The highest rate constant was estimated for <i>p</i>-coumaric acid + ^•OH reaction, whereas the rest of the ^•OX species are more reactive with <i>o</i>-coumaric acid. On the basis of the calculated rate constants, H abstraction from a −OH group should be the main mechanism for the reactions involving ^•OCH₃, ^•OOH, and ^•OOCH₃ radicals. Nevertheless, the addition mechanism, which sometimes is not considered in theoretical studies on reactions of phenolic compounds with electrophilic species, could play a relevant role in the global mechanism of coumaric acid + ^•OH reactions

Selected properties of 19663 steel after various surface treatment types

Předmětem předložené práce je analýza vlivu různých typů povrchového zpracování na vybrané vlastnosti nástrojové oceli typu 19663 a nalezení jeho nejoptimálnější varianty. Za tímto účelem bylo pro každou studovanou verzi provedeno hodnocení mikročistoty, studium mikrostruktury pomocí světelné a řádkovací elektronové mikroskopie a zkoušení mikrotvrdosti HV0.2. Pro vybrané varianty bylo rovněž provedeno hodnocení tvrdosti HV1 a zkoušení tribologických vlastností materiálu. Nejvyšší mikrotvrdost byla zjištěna v materiálu laserově kaleném, zatímco nitridovaný materiál o větší tloušťce vrstvy a následně konvenčně kalený vykazoval nejlepší tribologické vlastnosti.The work is aimed at an analysis of properties of 19663 tool steel after various surface treatment types and finding the optimal variant of heat treatement. For this purpose, micro-purity evaluation, microstructure study using optical microscopy and scanning electron microscopy and micro-hardness testing HV0.2 were carried out. For the selected alternatives, the HV1 hardness test was also carried out and the tribological properties of the material were tested. The highest microhardness was detected in material quenched using laser, while material nitride with thicker layer and subsequently conventionally quenched showed the best tribological properties.636 - Katedra materiálového inženýrstvívýborn

Aggregation-Induced Enhanced Emission (AIEE) from <i>N</i>,<i>N</i>‑Octyl-7,7′-diazaisoindigo-Based Organogel

A new kind of low molecular-mass organic gelator (LMOG) π-electron-deficient <i>N</i>,<i>N</i>-octyl-7,7′-diazaisoindigo (<b>1</b>) with aggregation-induced enhanced emission (AIEE) phenomenon is described. This organogel is capable of self-assembling through intermolecular H-bonding and π–π interactions between diazaisoindigo molecules. Its rheological properties, X-ray diffraction pattern, optical properties and theoretical calculations were investigated. The AIEE effect is exhibited in fluorescence during the formation of the supramolecular organogel, which persisted in the xerogel state, and the spectral red-shifts suggest the formation of <i>J</i>-type aggregates during the gelation process via π–π interactions in microbelts or 3D networks. Fluorescence lifetime and quantum yield significantly increase from dilute solution to the aggregate state. From a theoretical perspective, the effect of the aggregation of <b>1</b> on the photophysical properties was also studied by means of the density functional theory (DFT). In this sense, the lowest energy electronic transitions were calculated for both the single molecule and different size aggregates in order to predict spectral shifts. In addition, the geometry and molecular properties of the excited state were analyzed in different material states

DFT Study of the Ambipolar Character of Polymers on the Basis of s‑Tetrazine and Aryl Rings

The semiconducting character of a set of polymers based on alternating s-tetrazine (Tz) and aryl (Ar) rings has been studied by means of density functional theory (DFT) calculations. This work is aimed at the study of the role that the nature of the Ar substituents exerts on the molecular structure, crystal packing and semiconducting properties of these polymers. The modeling of the crystal structures allowed to analyze the relative arrangement of the polymer chains and its influence on the charge transport efficiency. As a result, the most efficient and balanced charge transport is predicted for a polymer based on alternating units of Tz and [1,3]­thiazolo­[5,4-<i>d</i>]­[1,3]­thiazole. Also, its narrow band gap and small difference between electron affinity and ionization potential lead us to propose that polymer as a candidate to be an ambipolar organic semiconductor

A Tuned LRC-DFT Design of Ambipolar Diketopyrrolopyrrole-Containing Quinoidal Molecules Interesting for Molecular Electronics

This work presents a Density Functional Theory (DFT) study on the charge transport related properties of two quinoidal diketopyrrolopyrrole (DPP) based systems. System <b>A</b>, recently synthesized, shows high efficiency as <i>n</i>-type organic semiconductor material while system <b>B</b>, not synthesized yet, has a linking benzothiadiazole (BT) unit between DPP moieties and would display an ambipolar character. The use of tuned, long-range corrected (LRC) functionals allows one to predict HOMO, LUMO, and charge transport properties for compound <b>A</b> in concordance with those experimentally observed. The use of BT building blocks allows for a conclusion that compound <b>B</b> is expected to display balanced and efficient charge injection along with high mobilities both for holes and electrons, which points to its potential to obtain high performances as an ambipolar semiconductor

Theoretical Approach to the Study of Thiophene-Based Discotic Systems As Organic Semiconductors

The main parameters that control charge transport at the molecular level have been studied for a series of columnar mesophase, thiophene-based discotic systems at semiempirical and DFT levels using different approximations, i.e., the dimer model and isolated molecule calculations. Charge carrier mobility was estimated through the charge transfer constant evaluated according to the semiclassical Marcus theory and compared to that obtained for a reference compound, i.e., triphenylene derivative. A set of different density functionals has been essayed in order to search for general patterns for charge transport related properties. In summary, only the compound with four thiophene rings, RO-TetraT, shows a significant increase in p character in comparison to the triphenylene derivative

pH-Sensitive Fluorescence Lifetime Molecular Probes Based on Functionalized Tristyrylbenzene

The dependence of the fluorescence on pH for two 1,3,5-tristyrylbenzenes decorated with polyamine (compound <b>1</b>) and poly­(amidoamine) (compound <b>2</b>) chains at the periphery was investigated. The highest fluorescence intensities were observed under acidic conditions because electrostatic repulsions between positively charged molecules reduce the fluorescence quenching. The slopes observed in the fluorescence pH titration curves were associated with deprotonation of the different types of amine groups, which results in quenching by photoinduced electron transfer and aggregation processes. The linear dependence of fluorescence lifetime observed for different pH ranges is a valuable property for applications in the field of fluorescence lifetime sensors and imaging microscopy. The influence of the pH and the peripheral chains on the aggregation processes was also analyzed by absorption and emission spectroscopy, dynamic light scattering measurements, and transmission electron microscopy. For compound <b>1</b>, bands associated with the formation of aggregates were detected along with micrometric aggregates surrounded by fibers with lattice fringes typical of columnar mesophases. For compound <b>2</b>, which contains longer peripheral chains with a higher degree of branching, aggregates with lower internal order were observed. In this case, the peripheral chains hindered aggregation by π-stacking although the amine groups did allow hydrogen bonding

Electronic Structure and Charge Transport Properties of a Series of 3,6-(Diphenyl)‑<i>s</i>‑tetrazine Derivatives: Are They Suitable Candidates for Molecular Electronics?

Optoelectronic and charge-transport related properties of a series of 3,6-diphenyl-<i>s</i>-tetrazine derivatives, including F, Cl, Br, and CN substituents, have been analyzed. The molecular structure and electronic properties of the new fluorine-containing derivative, bis­(3,6-difluorophenyl)-<i>s</i>-tetrazine, were explored by spectroscopic, electrochemical, and theoretical methods. The effects of the substituent on the pristine compound have been assessed from a theoretical perspective, showing that the fluorinated and brominated derivatives have the highest predicted electron mobilities, whereas the cyano derivative is foreseen to undergo the most efficient electron injection process

Effect of the Aggregation on the Photophysical Properties of a Blue-Emitting Star-Shaped Molecule Based on 1,3,5-Tristyrylbenzene

In this work we present a study on the effect of the aggregation on the optical properties of star-shaped molecules. We analyzed the modification of the absorption and fluorescent properties of a 1,3,5-tristyrylbenzene core due to the formation of diverse aggregates. The nature of the aggregates in solution was investigated by different spectroscopic techniques such as electronic absorption, steady-state fluorescence, fluorescence anisotropy, time-resolved fluorescence, small-angle X-ray scattering, and dynamic light-scattering spectroscopy. In order to simulate the molecular arrangement of the aggregates, the structure and electronic properties of different clusters formed by stacking of star-shaped molecules were studied by means of density functional theory calculations. The theoretical insight was performed in the gas phase as well as in solution through the polarizable continuum model, and both linear response and state-specific polarization schemes were applied. In the solid state, high quantum yields of up to 0.51 were measured for a 1,3,5-tristyrylbenzene derivative. Finally, the morphological properties of different solid samples were analyzed by differential scanning calorimetry, as well as scanning and transmission electron microscopies