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For nearly 50 years, the vision of using single molecules in circuits has been seen as providing the ultimate miniaturization of electronic chips. An advanced example of such a molecular electronics chip is presented here, with the important distinction that the molecular circuit elements play the role of general-purpose single-molecule sensors. The device consists of a semiconductor chip with a scalable array architecture. Each array element contains a synthetic molecular wire assembled to span nanoelectrodes in a current monitoring circuit. A central conjugation site is used to attach a single probe molecule that defines the target of the sensor. The chip digitizes the resulting picoamp-scale current-versus-time readout from each sensor element of the array at a rate of 1,000 frames per second. This provides detailed electrical signatures of the single-molecule interactions between the probe and targets present in a solution-phase test sample. This platform is used to measure the interaction kinetics of single molecules, without the use of labels, in a massively parallel fashion. To demonstrate broad applicability, examples are shown for probe molecule binding, including DNA oligos, aptamers, antibodies, and antigens, and the activity of enzymes relevant to diagnostics and sequencing, including a CRISPR/Cas enzyme binding a target DNA, and a DNA polymerase enzyme incorporating nucleotides as it copies a DNA template. All of these applications are accomplished with high sensitivity and resolution, on a manufacturable, scalable, all-electronic semiconductor chip device, thereby bringing the power of modern chips to these diverse areas of biosensing., Competing Interests: Competing interest statement: All authors having the Roswell affiliation (affiliation “a”) are employed by Roswell Biotechnologies, San Diego, CA 92121., (Copyright © 2022 the Author(s). Published by PNAS.)

Scaling up community-based participatory research (CBPR) remains challenging. This case-study reports on how, and under which conditions, a CBPR project aiming at promoting exercise among socially disadvantaged women (BIG) scaled up at four project sites. As part of BIG, researchers support city administrations in implementing a participatory project to reach socially disadvantaged women for exercise. The case study was conducted in winter 2020 in southern Germany and is based on a co-creative process involving city administrators and researchers. Following Kohl and Cooley's scaling up dimensions, scaling up BIG was investigated at the four sites using a mixed-method approach. Course registrations and offers were analysed, and qualitative interviews ( n = 4) with administrative staff members were conducted and analysed using content analysis. The geographical coverage of exercise classes, the addressed groups, and the utilisation of participatory methods by city administrations are described. All four sites managed to scale-up project activities. Three of the four sites reported that further growth of the project was no longer possible due to limited resources. All sites attempted to reach a larger number of, and more diverse, women. One site managed to scale-up the use of participatory methods within the city administration. The following important facilitators for scaling up CBPR projects were reported: advertisements tailored to the needs of the addressed women, utilising participatory approaches, and equipping project coordinators with sufficient resources.

Four decades after the first (and only) reported synthesis of kekulene, this emblematic cycloarene has been obtained again through an improved route involving the construction of a key synthetic intermediate, 5,6,8,9-tetrahydrobenzo[ m ]tetraphene, by means of a double Diels-Alder reaction between styrene and a versatile benzodiyne synthon. Ultra-high-resolution AFM imaging of single molecules of kekulene and computational calculations provide additional support for a molecular structure with a significant degree of bond localization in accordance with the resonance structure predicted by the Clar model.

The synthesis of a threefold symmetric nanographene with 19 cata-fused benzene rings distributed within six branches is reported. This flat dendritic starphene, which is the largest unsubstituted cata-condensed PAH that has been obtained to date, was prepared in solution by means of a palladium-catalyzed aryne cyclotrimerization reaction and it was characterized on surface by scanning probe microscopy with atomic resolution., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Rearrangements that change the connectivity of a carbon skeleton are often useful in synthesis, but it can be difficult to follow their mechanisms. Scanning probe microscopy can be used to manipulate a skeletal rearrangement at the single-molecule level, while monitoring the geometry of reactants, intermediates and final products with atomic resolution. We studied the reductive rearrangement of 1,1-dibromo alkenes to polyynes on a NaCl surface at 5 K, a reaction that resembles the Fritsch-Buttenberg-Wiechell rearrangement. Voltage pulses were used to cleave one C-Br bond, forming a radical, then to cleave the remaining C • -Br bond, triggering the rearrangement. These experiments provide structural insight into the bromo-vinyl radical intermediates, showing that the C=C • -Br unit is nonlinear. Long polyynes, up to the octayne Ph-(C≡C) 8 -Ph, have been prepared in this way. The control of skeletal rearrangements opens a new window on carbon-rich materials and extends the toolbox for molecular synthesis by atom manipulation.

Using scanning probe microscopy techniques, at low temperatures and in ultrahigh vacuum, individual molecules adsorbed on surfaces can be probed with ultrahigh resolution to determine their structure and details of their conformation, configuration, charge states, aromaticity, and the contributions of resonance structures. Functionalizing the tip of an atomic force microscope with a CO molecule enabled atomic-resolution imaging of single molecules, and measurement of their adsorption geometry and bond-order relations. In addition, by using scanning tunneling microscopy and Kelvin probe force microscopy, the density of the molecular frontier orbitals and the electric charge distribution within molecules can be mapped. Combining these techniques yields a high-resolution tool for the identification and characterization of individual molecules. The single-molecule sensitivity and the possibility of atom manipulation to induce chemical reactions with the tip of the microscope open up unique applications in chemistry, and differentiate scanning probe microscopy from conventional methods for molecular structure elucidation. Besides being an aid for challenging cases in natural product identification, atomic force microscopy has been shown to be a powerful tool for the investigation of on-surface reactions and the characterization of radicals and molecular mixtures. Herein we review the progress that high-resolution scanning probe microscopy with functionalized tips has made for molecular structure identification and characterization, and discuss the challenges it will face in the years to come., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Antiaromatic and open-shell molecules are attractive because of their distinct electronic and magnetic behaviour. However, their increased reactivity creates a challenge for probing their properties. Here, we describe the on-surface and in-solution generation and characterisation of a highly reactive antiaromatic molecule: indeno[1,2-b]fluorene (IF). In solution, we generated IF by KI-induced dehalogenation of a dibromo-substituted precursor molecule and found that IF survives for minutes at ambient conditions. Using atom manipulation at low temperatures we generated IF on Cu(111) and on bilayer NaCl. On these surfaces, we characterised IF by bond-order analysis using non-contact atomic force microscopy with CO-functionalised tips and by orbital imaging using scanning tunnelling microscopy. We found that the closed-shell configuration and antiaromatic character predicted for gas-phase IF are preserved on the NaCl film. On Cu(111), we observed significant bond-order reorganisation within the s-indacene moiety because of chemisorption, highlighting the importance of molecule surface interactions on the π-electron distribution.

We describe the generation of a meta-aryne at low temperature (T = 5 K) using atomic manipulation on Cu(111) and on bilayer NaCl on Cu(111). We observe different voltage thresholds for dehalogenation of the precursor and different reaction products depending on the substrate surface. The chemical structure is resolved by atomic force microscopy with CO-terminated tips, revealing the radical positions and confirming a diradical rather than an anti-Bredt olefin structure for this meta-aryne on NaCl.

Aiming to study new motifs, potentially active as functional materials, we performed the synthesis of a naphthodiazaborinine (the BN isostere of the phenalenyl anion) that is bonded to a hindered di-ortho-substituted aryl system (9-anthracene). We used atomic force microscopy (AFM) and succeeded in both the verification of the original nonplanar structure of the molecule and the planarization of the skeleton by removing H atoms that cause steric hindrance. This study demonstrated that planarization by atomic manipulation is a possible route for extending molecular identification by AFM to nonplanar molecular systems that are difficult to probe with AFM directly.

Abstract: The deposition of potassium onto TiO2(110) surface at 330K and the effects of post-annealing are investigated by scanning tunneling microscopy (STM), thermal desorption spectroscopy (TDS) and Auger-electron spectroscopy (AES). At lower K coverages (a few percentage of a monolayer), 3–4nm long and 1–2nm wide islands appear which can be identified with K covered regions. At higher K coverages, the surface exhibits disordered structures. Depending on the initial K coverage, the annealing above 700K in UHV results in ordering of the surface. For app. 1/3 monolayer K and annealing at around 900K, the entire surface reconstructs into a (1×2) phase accompanied by the appearance of pits with an average diameter of 20–30nm. This morphology is characteristic up to 1000K. Above this temperature, the recovery of the (1×1) phase was observed. At low K coverages (<0.2ML) the annealing at 1000K resulted in the formation of protruding islands of approximately 2×2nm2 which were identified with a strongly bonded surface compound containing K. [Copyright &y& Elsevier]

Abstract: Tunneling induced decomposition of Mo(CO)6 from the gas phase was studied on TiO2(110) surface by scanning tunneling microscopy (STM) and spectroscopy (STS). The efficiency of the procedure was followed by measuring the dot volume as a proportional indicator of the amount of the decomposed precursor. It was found that below 1 × 10−5 Pa background pressure of Mo(CO)6, there is no measurable effect and above 1 × 10−4 Pa, the nanodot size is too large compared to the curvature of the tip (20–40 nm). A threshold bias of +3.1(±0.1) V on the sample was measured for the decomposition of Mo(CO)6 in gas ambient. In the absence of the precursor, dot formation was observed only above +3.7(±0.2) V, in good agreement with the results reported in our earlier work about nanolithography on clean TiO2(110) substrate (E. Kriván, A. Berkó: J. Vac. Sci. & Tech. B 15(1) (1997)25). By applying voltages in the range of 3.1–3.5 V, a systematic enlargement of the created nanodots was found in the range of 2–20 s of duration and 0.01–1.0 nA of tunneling current. The I–V curves detected on the top of the nanodots have shown that the created features are of insulator character. This observation indicates that the decomposition of Mo(CO)6 is also accompanied by oxidation of the deposited Mo species. [Copyright &y& Elsevier]

We investigated single-layer graphene on SiC(0001) by atomic force and tunneling current microscopy, to separate the topographic and electronic contributions from the overall landscape. The analysis revealed that the roughness evaluated from the atomic force maps is very low, in accord with theoretical simulations. We also observed that characteristic electron scattering effects on graphene edges and defects are not accompanied by any out-of-plane relaxations of carbon atoms.

The current study investigates the influence of several R substituents (e.g., Me, SiH3, F, Cl, Br, OH, NH2, etc.) on the aromaticity of borazine, also known as the "inorganic benzene". By performing hybrid DFT methods, blended with several computational techniques, e.g., Natural Bond Orbital (NBO), Quantum Theory of Atoms in Molecules (QTAIM), Gauge-Including Magnetically Induced Current (GIMIC), Nucleus-Independent Chemical Shift (NICS), and following a simultaneous evaluation of four different aromaticity indices (para-delocalization index (PDI), multi-centre bond order (MCBO), ring current strength (RCS), and NICS parameters), it is emphasized that the aromatic character of B-substituted (B3R3N3H3) and N-substituted (B3H3N3R3) borazine derivatives can be tailored by modulating the electronic effects of R groups. It is also highlighted that the position of R substituents on the ring structure is crucial in tuning the aromaticity. Systematic comparisons of calculated aromaticity index values (i.e., via regression analyses and correlation matrices) ensure that the reported trends in aromaticity variation are accurately described, while the influence of different R groups on electron delocalization and related aromaticity phenomena is quantitatively assessed based on NBO analyses. The most relevant interactions impacting the aromatic character of investigated systems are (i) the electron conjugations occurring between the p lone pair electrons (LP) on the F, Cl, Br, O or N atoms, of R groups, and the π*(B=N) orbitals on the borazine ring (i.e., LP(R)→π*(B=N) donations), and (ii) the steric-exchange (Pauli) interactions between the same LP and the π(B=N) bonds (i.e., LP(R)↔π(B=N) repulsions), while inductive/field effects influence the aromaticity of the investigated trisubstituted borazine systems to a much lesser extent. This work highlights that although the aromatic character of borazine can be enhanced by grafting electron-donor substituents (F, OH, NH2, O−, NH−) on the N atoms, the stabilization due to aromaticity has only a moderate impact on these systems. By replacing the H substituents on the B atoms with similar R groups, the aromatic character of borazine is decreased due to strong exocyclic LP(R)→π*(B=N) donations affecting the delocalization of π-electrons on the borazine ring. [ABSTRACT FROM AUTHOR]

Spinel ferrites demonstrate extensive applications in different areas, like electrodes for electrochemical devices, gas sensors, catalysts, and magnetic adsorbents for environmentally important processes. However, defects in the real spinel structure can change the many physical and chemical properties of spinel ferrites. Although the number of defects in a crystal spinel lattice is small, their influence on the vast majority of physical properties could be really decisive. This review provides an overview of the structural characteristics of spinel compounds (e.g., CoFe2O4, NiFe2O4, ZnFe2O4, Fe3O4, γ–Fe2O3, Co3O4, Mn3O4, NiCo2O4, ZnCo2O4, Co2MnO4, etc.) and examines the influence of defects on their properties. Attention was paid to the classification (0D, 1D, 2D, and 3D defects), nomenclature, and the formation of point and surface defects in ferrites. An in-depth description of the defects responsible for the physicochemical properties and the methodologies employed for their determination are presented. DFT as the most common simulation approach is described in relation to modeling the point defects in spinel compounds. The significant influence of defect distribution on the magnetic interactions between cations, enhancing magnetic properties, is highlighted. The main defect-engineering strategies (direct synthesis and post-treatment) are described. An antistructural notation of active centers in spinel cobalt ferrite is presented. It is shown that the introduction of cations with different charges (e.g., Cu(I), Mn(II), Ce(III), or Ce(IV)) into the cobalt ferrite spinel matrix results in the formation of various point defects. The ability to predict the type of defects and their impact on material properties is the basis of defect engineering, which is currently an extremely promising direction in modern materials science. [ABSTRACT FROM AUTHOR]

The objective of this research is to determine how to obtain magnetic iron nanoparticles through the coprecipitation technique using FeCl3 and FeSO4 as raw materials in an aqueous extract of purple corn (Zea mays L) as a stabilizing state. In recent decades, the manufacture and use of magnetic iron nanoparticles has created great importance and expectation due to their various applications in different areas, among which stands out their ability to eliminate waste that pollutes the environment. Because research design is experimental in nature due to the different samples carried out in laboratories. The selection of corn was randomized due to the ease of access to the product from a group of farmers who were previously trained to plant, cultivate, harvest, and dry purple corn. The corn antioxidants were extracted with boiling water, and the synthesis of the nanoparticles was performed by mixing FeCl3, FeSO4 in the extract solution at a temperature of 25°C for 30 min with agitation at a pH above 11 with the addition of NaOH. Characterization was performed by UV-Vis spectrophotometer. The coprecipitation method produced the magnetic iron nanoparticles using FeCl3 and FeSO4 as reagents and the aqueous extract of purple corn. The practical implications that this research will have are diverse, as theoretically it will be possible to carry out experiments with other types of corn to see the different results, as well as to use it to carry out different tests in places highly contaminated with heavy metals. [ABSTRACT FROM AUTHOR]

In this paper, we show that simultaneous noncontact atomic force microscopy (nc-AFM) and scanning tunneling microscopy (STM) is a powerful tool for molecular discrimination on the Si(111)-7 × 7 surface, even at room temperature. Using density functional theory modeling, we justify this approach and show that the force response allows us to distinguish straightforwardly between molecular adsorbates and common defects, such as vacancies. Finally, we prove that STM/nc-AFM method is able to determine attachment sites of molecules deposited on semiconductor surface at room temperature.

In this paper we present a comparison of three different methods that can be used for estimating the stiffness of qPlus sensors. The first method is based on continuum theory of elasticity. The second (Cleveland's method) uses the change in the eigenfrequency that is induced by the loading of small masses. Finally, the stiffness is obtained by analysis of the thermal noise spectrum. We show that all three methods give very similar results. Surprisingly, neither the gold wire nor the gluing give rise to significant changes of the stiffness in the case of our home-built sensors. Furthermore we describe a fast and cost-effective way to perform Cleveland's method. This method is based on gluing small pieces of a tungsten wire; the mass is obtained from the volume of the wire, which is measured by optical microscopy. To facilitate detection of oscillation eigenfrequencies under ambient conditions, we designed and built a device for testing qPlus sensors.

Chemical identification of individual atoms in mixed In-Sn chains grown on a Si(100)-(2 × 1) surface was investigated by means of room temperature dynamic noncontact AFM measurements and DFT calculations. We demonstrate that the chemical nature of each atom in the chain can be identified by means of measurements of the short-range forces acting between an AFM tip and the atom. On the basis of this method, we revealed incorporation of silicon atoms from the substrate into the metal chains. Analysis of the measured and calculated short-range forces indicates that even different chemical states of a single atom can be distinguished.

We present the results of simultaneous scanning-tunneling and frequency-modulated dynamic atomic force microscopy measurements with a qPlus setup. The qPlus sensor is a purely electrical sensor based on a quartz tuning fork. If both the tunneling current and the force signal are to be measured at the tip, a cross-talk of the tunneling current with the force signal can easily occur. The origin and general features of the capacitive cross-talk will be discussed in detail in this contribution. Furthermore, we describe an experimental setup that improves the level of decoupling between the tunneling-current and the deflection signal. The efficiency of this experimental setup is demonstrated through topography and site-specific force/tunneling-spectroscopy measurements on the Si(111) 7×7 surface. The results show an excellent agreement with previously reported data measured by optical interferometric deflection.

Rh-Au core-shell nanoparticles were fabricated on TiO(2)(110) surface by physical vapor deposition (PVD) of Rh followed by exposure of Au at elevated sample temperature (500 K). The morphology of the bimetallic particles was checked by scanning tunneling microscopy (STM). The chemical composition of the particles was characterized by low energy ion scattering (LEIS) method. It was shown that the "seeding + growing" method described previously for growth of monometallic particles in narrow size distribution (Berko, A. et al. J. Catal. 1999, 182, 511) can also be applied for fabrication of bimetallic nanoparticles. The large mean free path of surface diffusion of gold on the oxide support makes the accumulation of Au possible exclusively on the Rh seeds formed in the first step of the procedure. By performing careful STM and LEIS experiments, it was proven that, for appropriate Au and Rh coverages, the postdeposited Au completely and uniformly covers the Rh nanoparticles.

In this study, we investigated the surface-confined coupling reactions of 1,8-dibromobiphenylene (BPBr2) on Cu(111) to elucidate the details of the organometallic intermediates via Ullmann reactions. We used scanning tunneling microscopy (STM) to characterize the resulting organometallic intermediates. Moreover, submolecular resolution of the non-contact atomic force microscopy (nc-AFM) qPlus technique enables the bond-resolving within the organometallic dimer product. Our findings reveal the debromination of BPBr2 on Cu(111), leading to the formation of an organometallic dimer intermediate at room temperature. Through nc-AFM measurements, we confirm and visualize the formation of the C-Cu-C bond. These insights enhance our understanding of Ullmann reaction and hold potential implications for the design of novel two-dimensional electronic devices. [ABSTRACT FROM AUTHOR]

Copyright of Public Health Forum is the property of De Gruyter and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The electronic, optical, and anticorrosion properties of planer ZnO crystal and quantum dots are explored using density functional theory calculations. The calculations for the finite ZnO quantum dots were performed in Gaussian 16 using the B3LYP/6-31g level of theory. The periodic calculations were carried out using VASP with the plane wave basis set and the PBE functional. The subsequent band structure calculations were performed using the hybrid B3LYP functional that shows accurate results and is also consistent with the finite calculations. The considered ZnO nanodots have planer hexagonal shapes with zigzag and armchair terminations. The binding energy calculations show that both structures are stable with negligible deformation at the edges. The ZnO nanodots are semiconductors with a moderate energy gap that decreases when increasing the size, making them potential materials for anticorrosion applications. The values of the electronic energy gaps of ZnO nanodots are confirmed by their UV-Vis spectra, with a wide optical energy gap for the small structures. Additionally, the calculated positive fraction of transferred electrons implies that electron transfer occurs from the inhibitor (ZnO) to the metal surface to passivate their vacant d-orbitals, and eventually prevent corrosion. The best anti-corrosion performance was observed in the periodic ZnO crystal with a suitable energy gap, electronegativity, and fraction of electron transfer. The effects of size and periodicity on the electronic and anticorrosion properties are also here investigated. The findings show that the anticorrosion properties were significantly enhanced by increasing the size of the quantum dot. Periodic ZnO crystals with an appropriate energy gap, electronegativity, and fraction of electron transfer exhibited the optimum anticorrosion performance. Thus, the preferable energy gap in addition to the most promising anticorrosion parameters imply that the monolayer ZnO is a potential candidate for coating and corrosion inhibitors. [ABSTRACT FROM AUTHOR]

Isomers of stilbenes containing phenalenyl substituents in the para- and meta-positions of phenyl rings have been studied by means of the density functional theory method. Exchange coupling in the structures with the trans-form of stilbenes has been absent. In the cis-isomer of a meta-substituted compound, the state with a closed electron shell has been stabilized due to two-electron multicenter interactions, as confirmed by the CASSCF calculations. The predicted transition between the triplet and singlet states due to the trans-cis isomerization opens the prospects for using the discovered effect in the development of organic spin switches. [ABSTRACT FROM AUTHOR]

Cycloarene molecules are benzene-ring-based polycyclic aromatic hydrocarbons that have been fused in a circular manner and are surrounded by carbon–hydrogen bonds that point inward. Due to their magnetic, geometric, and electronic characteristics and superaromaticity, these polycyclic aromatics have received attention in a number of studies. The kekulene molecule is a cyclically organized benzene ring in the shape of a doughnut and is the very first example of such a conjugated macrocyclic compound. Due to its structural characteristics and molecular characterizations, it serves as a great model for theoretical research involving the investigation of π electron conjugation circuits. Therefore, in order to unravel their novel electrical and molecular characteristics and foresee potential applications, the characterization of such components is crucial. In our current research, we describe two unique series of enormous polycyclic molecules made from the extensively studied base kekulene molecule, utilizing the essential graph-theoretical tools to identify their structural characterization via topological quantities. Rectangular kekulene Type-I and rectangular kekulene Type-II structures were obtained from base kekulene molecules arranged in a rectangular fashion. We also employ two subcases for each Type and, for all of these, we derived ten topological indices. We can investigate the physiochemical characteristics of rectangular kekulenes using these topological indices. [ABSTRACT FROM AUTHOR]

Cycloarenes such as kekulenes, septulenes and extended kekulenes are of considerable interest as they are precursors to holey nanographene with pores of variable sizes with interesting electronic and magnetic properties. These systems have also been of interest due to aromaticity, ring currents arising from π -electrons and intriguing topological properties. This study's primary objective is to determine the topological properties including entropies through analytical expressions of degree-based entropy metrics for two well-known classes of tessellations of kekulenes. The various topological indices and entropies obtained here to shed light on the underlying topological connectivities and molecular structural features. It is shown that the rhomboidal tessellations exhibit greater entropies compared to triangular tessellations. Applications of the developed techniques to machine learning of NMR and ESR spectra of these tessellations are pointed out. [ABSTRACT FROM AUTHOR]

The morphology and void connectivity of thin films grown by a magnetron sputtering deposition technique at oblique geometries were studied in this paper. A well-tested thin film growth model was employed to assess the features of these layers along with experimental data taken from the literature. A strong variation in the film morphology and pore topology was found as a function of the growth conditions, which have been linked to the different collisional transport of sputtered species in the plasma gas. Four different characteristic film morphologies were identified, such as (i) highly dense and compact, (ii) compact with large, tilted mesopores, (iii) nanocolumns separated by large mesopores, and (iv) vertically aligned sponge-like coalescent nanostructures. Attending to the topology and connectivity of the voids in the film, the nanocolumnar morphology was shown to present a high pore volume and area connected with the outside by means of mesopores, with a diameter above 2 nm, while the sponge-like nanostructure presented a high pore volume and area, as well as a dense network connectivity by means of micropores, with a diameter below 2 nm. The obtained results describe the different features of the porous network in these films and explain the different performances as gas or liquid sensors in electrochromic applications or for infiltration with nanoparticles or large molecules. [ABSTRACT FROM AUTHOR]

In this work, we theoretically investigate the linear and nonlinear optical absorption properties of open triangulene spin chains and cyclic triangulene spin chains in relation to their lengths and shapes. The physical mechanism of local excitation within the triangular alkene unit and the weak charge transfer between the units are discussed. The uniformly distributed electrostatic potential allows the system to have a small permanent dipole moment that blocks the electronic transition in the light excitation such that the electronic transition can only be carried out between adjacent carbon atoms. The one-photon absorption (OPA) spectra and two-photon absorption (TPA) spectra are red-shifted with the addition of triangulene units compared to N = 3TSCs (triangulene spin chains, TSCs). Here, TPA is mainly caused by the first step of the transition. The length of the spin chain has a significant adjustment effect on the photon cross-section. TSCs of different lengths and shapes can control chirality by adjusting the distribution of the electric dipole moment and transition magnetic dipole moment. These analyses reveal the photophysical properties of triangulene and provide a theoretical basis for studying the photophysical properties of triangulene and its derivatives. [ABSTRACT FROM AUTHOR]

Many natural oxidations are relevant to the origin and running of life but usually proceeded under mild conditions using molecular oxygen (O2) in the air as the sole oxidant and enzymes as the catalysts. In modern society, catalysis plays an essential role in many industries, such as chemical and pharmaceutical industries. However, most heterogeneous catalytic reactions need high operational reaction temperature and pressure. Research interest is redirected to green catalysis in recent years, e.g., running catalytic reactions under mild conditions, employing green solvents and green oxidants such O2, particularly air. One question always exists: can these industrial catalytic processes be ultimately run similar to the natural oxidation processes in efficiency and operation conditions? For many catalytic oxidation reactions, the greatest challenge lies in activating molecular oxygen under mild conditions. Therefore, a molecular-level understanding of the interactions of O2 molecules with catalysts or substrates is necessary and crucial. In this review, we discuss the activation of O2 to different active species (e.g., O22− or O22−) and their participation in low-temperature (≤300 oC) catalytic oxidation reactions. The challenges, recent progress, and trends in some low-temperature oxidation reactions are discussed and highlighted. The early studies on the activation of oxygen on various catalysts mainly paid attention to the interaction between the molecular oxygen and the oxygen vacancies of metal oxides. In contrast, recent studies try to fully understand the generation, measurement, and catalytic roles of the various active oxygen species. Therefore, the design of catalysts that can facilely activate O2 at low temperatures is of importance. With such catalysts, it is possible to reduce the high energy consumption, improve the selectivity of catalytic oxidations, and ultimately realize the industrial oxidation reactions at conditions as mild as possible to that of many natural oxidation processes. Finally, from the current body of knowledge, we propose future directions that can effectively utilize O2 for solving practical problems at low temperatures and help understand the oxidation catalysis at the molecular level. [ABSTRACT FROM AUTHOR]

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