Delocalization Research Articles

Probability Density Analysis Reveals Substantial Differences Between the Dinitrogen and Acetylene Triple Bonds.

In earlier publications, it was shown that the electron positions maximizing the probability density resemble the Lewis structures for most small molecules. While this holds for the triple bond in acetylene, this is not the case for the triple bond in dinitrogen. Because of recent advances in studying the topology of wave functions, this peculiar case is revisited. In this work, the dinitrogen wave function is analyzed and compared to that of acetylene. Significant differences of the electron positions maximizing are uncovered and explained by the presence of hydrogen atoms in acetylene and by electron arrangements resulting from calculations of the nitrogen and carbon atoms. Moreover, insights into the electron delocalization of both molecules are gained by investigating electron exchange paths. Considering the different chemical behaviors of dinitrogen and acetylene, these differences should be expected.

Impact of Molecular Structure on Generation in D–A Heterojunction Photocatalysts for Efficient Dye Degradation under Weak Light

AbstractThe dual challenges of photocatalysis technology in addressing wastewater pollution and the energy crisis demand advanced photocatalysts with enhanced visible light absorption and efficient charge separation. This work utilizes bulk‐heterojunction organic solar cell (BHJ‐OSCs) active layers as photocatalytic sources, presenting PM6:PIID‐ClBF@BC, a biochar‐supported donor‐acceptor (D‐A) heterojunction organic photocatalyst, designed for water phototreatment and clarify the impacts of molecular structure on photocatalytic activity, simultaneously assist with challenges associated with OSCs waste disposal and resource secondary expansion. PM6:PIID‐ClBF@BC achieves complete RhB degradation within 10 minutes and maintains nearly 100% over 20 cycles. Additionally, it generated 28.15 µmol of H₂ within 3 hours, corresponding to a rate of 187.67 µmol h⁻¹ g⁻¹. The superior performance is attributed to its broader visible‐light absorption, increased electronegativity (enhanced dipole moment) induced by chlorine substitution, and favorable stacking interactions provide larger electron delocalization, forming a strong internal electric field that drives efficient charge separation and intramolecular charge transfer thereby enhancing reactive oxygen species generation. Electrostatic interactions between PM6:PIID‐ClBF@BC and RhB facilitate effective adsorption and catalysis, with higher superoxide radical levels driving degradation. This highlights the crucial role of molecular structure in optimizing photocatalytic performance, offering insights for designing next‐generation photocatalysts for environmental remediation and sustainable energy.

Theoretical investigation on carbene-catalyzed [3 + 3] annulation of vi-nyl sulfoxonium ylide with enal for synthesis of 2-sulfenylidene-3-cyclohexen-1-one

The first theoretical investigation was provided by our DFT calculation on trazolum carbene-catalyzed [3 + 3] annulation of vinyl sulfoxonium ylide with enal. Free carbene NHC is formed via deprotonation by BF4 with enhanced nucleophilicity. NHC attacks positive carbonyl of enal with its negative carbon followed by proton transfer leading to Breslow intermediate, which is easily transformed to α, β-unsaturated acylazolium inter-mediate through dehydrogenation. Spontaneous electron delocalization in vinyl sulfoxonium ylide makes car-banion available at α-position of ester. Michael addition undergoes linking two substrates. Followed by pro-ton shift, the carbanion attacks positive carbonyl in crucial ring closure yielding six-membered carbocycle. The second proton shift generates isomer of desired 2-sulfenylidene-3-cyclohexen-1-one after release of proto-nated NHC.

Pr doping promotes the formation of Pt single atoms by regulating metal-support interaction for remarkable photocatalytic hydrogen production

Since the metal-support interaction (MSI) has a great influence on the structure and properties of single atom catalysts (SACs), the activity and stability of SACs can be effectively regulated by adjusting the structure of the matrix. Herein, the morphology of surface supported Pt species can be controlled by doping to adjust the properties of TiO2 support. Specifically, under the same conditions, the Pt species on the Pr doped TiO2 surface are Pt SAs (PtSA/TiO2(Pr)), while on the pure TiO2 surface are particles (PtNP/TiO2). Experimental and theoretical studies demonstrate that Pr doping weakens the interaction of Ti-O bond, stabilizes the O-Pt unit site and Pt SAs. Impressively, PtSA/TiO2(Pr) shows superior photocatalytic hydrogen production performance (196.43 mmol g-1h−1), far exceeding PtNP/TiO2 (91.96 mmol g-1h−1). Additionally, Pr dopant modulates the electronic interaction between TiO2 support and Pt SAs, thus the adsorption/desorption behavior of H intermediates (H*) is balanced. Besides, the electron delocalization of O adjacent to Pt SAs can be adjusted by Pr doping, prompting the establishment of efficient Pt-O electron transfer channels and further enhances the utilization of photogenerated carriers. This study presents a promising strategy to prepare SACs with high activity for photocatalyst hydrogen production.

Reconsideration of the P-clusters in VFe proteins using the bond-valence method: towards their electron transfer and protonation.

P-clusters have been statistically analysed using the bond-valence sum (BVS) method together with weighting schemes. The crystallographic data come from the VFe proteins deposited in the Protein Data Bank (PDB) with high resolutions of better than 1.35 Å. Calculations show that the formal oxidation state of a P1+ cluster can be assigned as 2Fe3+6Fe2+ with high electron delocalization, giving the same oxidation state as that of PN clusters in VFe proteins. Further comprehensive comparisons of the bond distances suggest that the hydroxyl groups of the β-153 serine residues in P1+ and PN clusters are in the protonated state, where the Fe6 atoms have the same oxidation state as Fe2+. During the transition from PN to P1+, cleavage of the Fe6-S1 bond is accompanied by the formation of a weak coordination between the Fe6 atom and the hydroxyl group of the β-153 serine residue in the P1+ cluster of the VFe protein. Similarly, oxidation of PN to P1+/P2+ clusters corresponds to the coordination of Fe6(II) by the hydroxyl group of the β-188 serine residue and of Fe5(II) by the peptide amine group of the α-88 cysteine residue in the MoFe protein of Azotobacter vinelandiis without electron and proton transfers.

Large Faraday Rotation in Pyrolysis Synthesized Carbon Dots

Pyrolysis of citric acid produced carbon dots on the 10 nm size scale, tunable by synthesis time. Magneto-optical spectroscopy revealed a size-dependent Faraday rotation. For particles with optimal synthesis time, the Verdet constant was measured as >300 times larger than that of water on a per-mass basis. Introducing ethylenediamine substrate as a nitrogen dopant in the synthesis resulted in a similar effect. These behaviors are indicative of extended sp2 networks in the particles. A strong wavelength dependence with largest rotation at the shortest measured wavelength of 405 nm was observed. This dependence is explained by a comparison with the theory of electron-photon interactions, which predicts an increase of the Verdet constant with 1/(ω02-ω2)2 for an angular frequency ω and an absorption line at ω0. The fitting of the analytical function to the measured Faraday rotation indicates a wavelength near 300 nm corresponding to the ω0, consistent with an extended electron delocalization. Nanomaterials with large magneto-optical effects have new proposed technological applications, such as in their use as magnetic field sensors. The Faraday rotation is related to spin-induced effects, foremost nuclear spin optical rotation, suggesting further applications of these materials for the optical readout of spin states in quantum information science.

Polarization Switching from Valence Trapping in an Oxo-Bridged Trinuclear Iron Complex.

Switching electric polarization by external stimuli constitutes a technical foundation for various applications. Here, we reported the observation of polarization-switching behavior in an oxo-bridged mixed-valence complex [Fe3O(piv)6(py)3] (piv = pivalate, py = pyridine). Detailed variable-temperature Mössbauer spectral analyses unambiguously confirm the occurrence of an electron localization-delocalization transition between two inequivalent Fe sites. Given that the compound crystallizes in a polar space group, the change in the molecular dipole moments leads to a pyroelectric effect observed during this transition, indicating thermally induced polarization switching behavior. As the complex exhibits asymmetry in the valence-active sites and antiferromagnetic interaction between them, the possibility of magnetoelectric coupling in this compound is also discussed on the basis of the recent prediction of polarization switching through modulating the degree of electron delocalization by magnetic fields in the mixed-valence systems.

Multiple Protophilic Redox‐Active Sites in Reticular Organic Skeletons for Superior Proton Storage

Protons (H+) with the smallest size and fastest redox kinetics are regarded as competitive charge carriers in the booming Zn‐organic batteries (ZOBs). Developing new H+‐storage organic cathode materials with multiple ultralow‐energy‐barrier protophilic sites and super electron delocalization routes to propel superior ZOBs is crucial but still challenging. Here we design multiple protophilic redox‐active reticular organic skeletons (ROSs) for activating better proton storage, triggered by intermolecular H‐bonding and π–π stacking interactions between 2,6‐diaminoanthraquinone and 2,4,6‐triformylphloroglucinol nanofibrous polymer. ROSs expose reticular electron delocalization geometries to fully access build‐in protophilic carbonyl sites and promote ultrarapid H+ migration with an ultralow activation energy (0.13 vs. 0.29 eV of Zn2+ ions), thus delivering high capacity (359 mAh g−1) and large‐current survivability (100 A g−1). Moreover, the extended interconnected reticular structures strengthen the anti‐dissolution of ROSs in aqueous electrolytes, affording long‐lasting proton‐storage activity in ZOBs to a superior level (60,000 cycles at 20 A g−1). Systematic studies identify the source of excellent charge storage as high‐kinetics H+‐coupled five‐electron redox process of carbonyl motifs in superstable ROSs. These findings can be of importance for evoking superior proton activity in multiple redox organics to build advanced Zn‐organic batteries.

Multiple Protophilic Redox-Active Sites in Reticular Organic Skeletons for Superior Proton Storage.

Protons (H+) with the smallest size and fastest redox kinetics are regarded as competitive charge carriers in the booming Zn-organic batteries (ZOBs). Developing new H+-storage organic cathode materials with multiple ultralow-energy-barrier protophilic sites and super electron delocalization routes to propel superior ZOBs is crucial but still challenging. Here we design multiple protophilic redox-active reticular organic skeletons (ROSs) for activating better proton storage, triggered by intermolecular H-bonding and π-π stacking interactions between 2,6-diaminoanthraquinone and 2,4,6-triformylphloroglucinol nanofibrous polymer. ROSs expose reticular electron delocalization geometries to fully access build-in protophilic carbonyl sites and promote ultrarapid H+ migration with an ultralow activation energy (0.13 vs. 0.29 eV of Zn2+ ions), thus delivering high capacity (359 mAh g-1) and large-current survivability (100 A g-1). Moreover, the extended interconnected reticular structures strengthen the anti-dissolution of ROSs in aqueous electrolytes, affording long-lasting proton-storage activity in ZOBs to a superior level (60,000 cycles at 20 A g-1). Systematic studies identify the source of excellent charge storage as high-kinetics H+-coupled five-electron redox process of carbonyl motifs in superstable ROSs. These findings can be of importance for evoking superior proton activity in multiple redox organics to build advanced Zn-organic batteries.

Modulating the Coordination Environment of Atomically Dispersed Nickel for Efficient Electrocatalytic CO2 Reduction at Low Overpotentials and Industrial Current Densities.

Electrocatalytic CO2-to-CO conversion with a high CO Faradaic efficiency (FECO) at low overpotentials and industrial-level current densities is highly desirable but a huge challenge over non-noble metal catalysts. Herein, graphitic N-rich porous carbons supporting atomically dispersed nickel (NiN4-O sites with an axial oxygen) were synthesized (denoted as O-Ni-Nx-GC) and applied as the cathode catalyst in a CO2RR flow cell. O-Ni-Nx-GC showed excellent selectivity with a FECO over 92% at low overpotentials ranging from 17 to 60 mV, and over 99% at 80 mV. The FECO was ∼100% at industrial-level current densities from 200 to 900 mA·cm-2. Impressively, O-Ni-Nx-GC delivered a state-of-the-art FECO of >96% at 1 A·cm-2 with a turnover frequency of 81.5 s-1 in a 1 M KOH electrolyte. O-Ni-Nx-GC offered excellent stability during long-term operation for 140 h at 100 mA·cm-2, maintaining a FECO > 99%. Mechanism studies revealed that the axial oxygen at the atomically dispersed nickel sites enhanced electron delocalization, with the graphitic N-rich porous carbon support lowering the CO2-to-CO energy barrier and inducing a negative shift in the Ni-3d d-band center, effectively promoting the formation of the *COOH intermediate while weakening the adsorption of the *CO intermediate, thus optimizing the catalytic activity/selectivity to CO under practical conditions.

Ground and excited state aromaticity in azulene-based helicenes.

Electron delocalization is studied in the ground singlet and first excited triplet states of azulene-containing helicenes. After showing that the compounds we study can be synthesized, we show that they exhibit a charge separation in the ground state, which does not appear in their triplet excited state. Then, magnetically induced properties (IMS3D and ACID) and electron density decomposition methods (EDDB) are used to rationalize aromaticity in these systems. For azulene-based helicenes larger than a critical size, that is, for more than six fused cycles, unexpected aromatic delocalization circuits appear. This feature is understood via the decomposition of the wavefunction on sets of carefully chosen local electronic structures and fragment orbital diagrams.

Revealing Local Structures of Chiral Molecules via X-ray Circular Dichroism.

Chirality is crucial due to its role in biological and chemical systems, where molecular handedness impacts structure and function. Chiral molecules with nonsuperimposable mirror images exhibit distinct biological activities pivotal in drug design and catalysis. This theoretical study explores X-ray circular dichroism (XCD) as a tool for probing the local structures of chiral molecules. We calculated the XCD signals at the chlorine, oxygen, and nitrogen K edges in various molecular systems. Our results show that electron delocalization plays an important role in the sensitivity of XCD to X-ray chromophore-chiral center distance. Furthermore, the XCD signals at multiple X-ray chromophores could offer multidimensional insights to pinpoint chiral center, providing spatial information about the local structures of complex chiral molecules.

Highly Efficient Degradation of Bisphenol A by Peroxymonosulfate Activation Using Bamboo Kraft Lignin Single-Atom Catalyst.

A nitrogen-coordinated Fe single-atom catalyst (SA Fe-N/C) is synthesized using a homogeneous ethanol-based dissolution system with bamboo kraft lignin serving as the carbon source. Uniformly dispersed Fe atoms with an interatomic distance of less than 2 Å throughout the SA Fe-N/C structure are revealed through X-ray absorption spectral analysis and HAADF-STEM images, which possessed a high Fe loading of 2.69%. The degradation rate of bisphenol A (BPA) approached 99% within 5 min, with the observed rate constant (kobs) of the catalysts markedly increasing from 0.070 to 0.615 min-1. The catalyst-mediated electron transfer pathway is identified as the predominant mechanism for BPA degradation. Both experimental data and DFT analysis of the nitrogen ligands demonstrated that pyridinic N-coordinated Fe single atoms are the principal active sites, attributed to the enhanced electron density and delocalization concentrated around the Fe sites. These findings significantly elucidate the role of nitrogen ligands in designing efficient lignin-derived carbon single-atom catalysts for environmental applications.

A highly sensitive and fast-response fluorescence nanoprobe for in vivo imaging of hypochlorous acid.

Fluorescent probes for in vivo hypochlorous acid (HClO) imaging often face challenges of low selectivity and high cytotoxicity, largely due to poor analyte recognition and water-insoluble aromatic skeletons. To address this, we synthesized fluorescein hydrazide by introducing a spiro-lactam unit into fluorescein, which offers high emission intensity and molar absorption. The five-membered heterocycle in fluorescein hydrazide is selectively disrupted by HClO, enhancing the conjugated system and electron delocalization of the fluorophore, resulting in highly sensitive fluorescence detection of HClO. For in vivo imaging, fluorescein hydrazide was covalently grafted onto the surface of silica nanoparticles via nucleophilic substitution reaction, avoiding complex modifications. This fluorescent nanoprobe (Si-FL) leverages the high-density fluorophores and hydroxyl groups on the silica surface to enrich low-concentrations of HClO through weak supramolecular interactions, thereby accelerating the reaction between HClO and the recognition sites. Compared to other molecular probes, Si-FL demonstrates a superior response speed (within 20 s) and a lower detection limit (72 nM), alongside excellent biocompatibility and water solubility. The nanoprobe Si-FL was successfully applied for HClO detection in living cells, zebrafish, and plants, significantly improving the stability of fluorescence imaging.

Mechanistic Insights into the Anticancer Potential of Methoxyflavones Analogs: A Review.

2-phenylchromen-4-one, commonly known as flavone, plays multifaceted roles in biological response that can be abundantly present in natural sources. The methoxy group in naturally occurring flavones promotes cytotoxic activity in various cancer cell lines by targeting protein markers, in facilitating ligand-protein binding mechanisms and activating cascading downstream signaling pathways leading to cell death. However, the lipophilic nature of these analogs is a key concern as it impacts drug membrane transfer. While lipophilicity is crucial for drug efficacy, the excessive lipophilic effects in flavonoids can reduce water solubility and hinder drug transport to target sites. Recent in vitro studies suggest that the incorporation of polar hydroxyl groups which can form hydrogen bonds and stabilize free radicals may help overcome the challenges associated with methoxy groups while maintaining their essential lipophilic properties. Naturally coexisting with methoxyflavones, this review explores the synergistic role of hydroxy and methoxy moieties through hydrogen bonding capacity in maximizing cytotoxicity against cancer cell lines. The physicochemical analysis revealed the potential intramolecular interaction and favorable electron delocalization region between both moieties to improve cytotoxicity levels. Together, the analysis provides a useful strategy for the structure-activity relationship (SAR) of flavonoid analogs in distinct protein markers, suggesting optimal functional group positioning to achieve balanced lipophilicity, effective hydrogen bonding, and simultaneously minimized steric hindrance in targeting specific cancer cell types.

Long-Range Charge Transport Facilitated by Electron Delocalization in MoS2 and Carbon Nanotube Heterostructures.

Controlling charge transport at the interfaces of nanostructures is crucial for their successful use in optoelectronic and solar energy applications. Mixed-dimensional heterostructures based on single-walled carbon nanotubes (SWCNTs) and transition metal dichalcogenides (TMDCs) have demonstrated exceptionally long-lived charge-separated states. However, the factors that control the charge transport at these interfaces remain unclear. In this study, we directly image charge transport at the interfaces of single- and multilayered MoS2 and (6,5) SWCNT heterostructures using transient absorption microscopy. We find that charge recombination becomes slower as the layer thickness of MoS2 increases. This behavior can be explained by electron delocalization in multilayers and reduced orbital overlap with the SWCNTs, as suggested by nonadiabatic (NA) molecular dynamics (MD) simulations. Dipolar repulsion of interfacial excitons results in rapid density-dependent transport within the first 100 ps. Stronger repulsion and longer-range charge transport are observed in heterostructures with thicker MoS2 layers, driven by electron delocalization and larger interfacial dipole moments. These findings are consistent with the results from NAMD simulations. Our results suggest that heterostructures with multilayer MoS2 can facilitate long-lived charge separation and transport, which is promising for applications in photovoltaics and photocatalysis.

Exploring and analyzing the causes of color in the earth

Color is an essential element of human visual perception, which exists in all aspects of our daily lives and plays a key role in scientific research and technological applications. Color is produced by various mechanisms, including absorption and reflection of chemical pigments, complex formation of transition metal ions, and micro- and nanostructural modulation of structural colors. This paper aims to comprehensively explore the scientific principles of color generation and its applications in different fields. The article first describes how transition metal ions exhibit colors by forming complexes and explains in detail the coordination process of copper ions in an aqueous solution and its resulting d-orbital splitting, which in turn absorbs light of specific wavelengths and exhibits complementary colors. Secondly, the article explores the mechanism of color expression of natural pigments in plants, significantly how pigment molecules containing conjugated double bonds, such as -carotene, can absorb specific wavelengths of light and exhibit vivid colors through electron delocalization and energy level jumps. Finally, the article illustrates the principles of structural color and its potential for industrial applications, including using micro- and nanostructures, such as photonic crystals, to modulate the scattering and absorption of light, thus enabling dynamic changes in color and environmental protection. The in-depth exploration of the mechanism of color generation enhances our understanding of the basic principles of color science. It provides theoretical support for technological innovation and practical applications in related fields.

Atomically Dispersed Fe-Mo Catalysts Mediate Fenton-Like Reaction to Efficiently Degrade Chlorophenol Pollutants Through Synergistic Oxidation and Dechlorination Reactions.

Chlorophenols are difficult to degrade and mineralize by traditional advanced oxidation processes due to the strong electronegativity of chlorine. Here, a dual-site atomically dispersed catalyst (FeMoNC) is reported, which Fe/Mo supported on mesoporous nitrogen-doped carbon is prepared through high-temperature migration. The FeMoNC exhibits a high dechlorination rate of 93.3% within 1 min. Theoretical calculation suggested that the doping of high-valence Mo6+ as the electron reservoir, promoted electronic delocalization at Fe sites, thereby enhancing the adsorption and dissociation of peroxymonosulfate (PMS), subsequent generation of Fe (IV) = O and singlet oxygen (1O2) species. An interesting finding is that Mo sites can adsorb chlorine sites in 4-chlorophenol (4-CP) and induce C─Cl bond fracture. Thus, the FeMoNC/PMS system has high catalytic performance due to the synergistic effects of Mo-induced dechlorination and non-radical species (Fe(IV) = O and 1O2) as the degradation pathways, the degradation efficiency of 99.1% of 4-CP within 5 min without significant performance decline after 168h ≈15,120-bed volumes. These findings can advance mechanistic understanding of PMS activation at the molecular level and guide the rational design of efficient eco-friendly single-atom catalysts (SACs) catalysts with bimetallic atomic sites.

A ladder-type organic molecule with pseudocapacitive properties enabling superior electrochemical desalination.

The availability of clean water is fundamental for maintaining sustainable environments and human ecosystems. Capacitive deionization offers a cost-effective, environmentally friendly, and energy-efficient solution to meet the rising demand for clean water. Electrode materials based on pseudocapacitive adsorption have attracted significant attention in capacitive deionization due to their relatively high desalination capacity. In this study, a novel organic compound, PTQN, is introduced, featuring a ladder-type structure enriched with imine-based active sites, specifically designed for capacitive deionization. This advanced molecular design imparts the PTQN compound with exceptional pseudocapacitive properties, enhanced electron delocalization, and superior structural stability, which are supported by both experimental results and theoretical analyses. As an electrode, PTQN exhibits a high pseudocapacitive capacitance of 238.26 F g-1 and demonstrates excellent long-term stability, retaining approximately 100 percent of its capacitance after 5000 cycles in NaCl solution. The involvement of PTQN active sites in the Na+ electrosorption process was further elucidated using theoretical calculations and ex situ characterization. Moreover, a hybrid capacitive deionization (HCDI) device employing the PTQN electrode exhibited an impressive salt removal capacity of 61.55 mg g-1, a rapid average removal rate of 2.05 mg g-1 min-1, and consistent regeneration performance (∼97.04 percent after 50 cycles), demonstrating its potential for capacitive deionization systems. Furthermore, the PTQN electrode displayed superior removal efficiency for tetracycline. This work contributes to the rational design of organic materials for the development of advanced electrochemical desalination systems.

Machine Learning Recognition of Artificial DNA Sequence with Quantum Tunneling Nanogap Junction.

Artificially synthesized DNA holds significant promise in addressing fundamental biochemical questions and driving advancements in biotechnology, genetics, and DNA digital data storage. Rapid and precise electric identification of these artificial DNA strands is crucial for their effective application. Herein, we present a comprehensive investigation into the electric recognition of eight artificial synthesized DNA (xDNA and yDNA) nucleobases using quantum tunneling transport and machine learning (ML) techniques. By embedding these nucleobases within a solid-state nanogap junction, we calculated their fingerprint transmission and current readouts and also analyzed the influence of electronic coupling and molecular orbital delocalization on these properties. The trained ML model achieved a predictive basecalling accuracy of up to 100% for xDNA nucleobases and 99.80% for yDNA transmission readout data sets. ML explainability study revealed that normalized descriptors have a greater impact on nucleobase prediction than the original transmission function, proving more effective in disentangling overlapping artificial DNA nucleobase signals. Quaternary classification results highlighted higher recognition accuracy for xDNA nucleobases than for yDNA nucleobases. Furthermore, precise calling of complementary, purine, and pyrimidine base pair combinations was demonstrated with high sensitivity and an F1 score. Our findings reveal the feasibility of highly sensitive and precise electrical recognition of artificial DNA nucleobases, which can transform genetic research and spur advancements in genetic data storage, synthetic biology, and diagnostics.