Electronic Transitions Research Articles

Synthesis, Characterization and Bioactivity Evaluation for Some Metal Ions Complexes with New Ligand Derived from 2-hydroxy-1- napthaldehyed

تم مفاعلة قاعدة شيف المُحضرة حديثًا (E)-2-((2-phenylhydrazono)methyl)naphthalen-1-ol (مشتق فينيل هيدرازين) مع كل من الأيونات المعدنية التالية: Ni2 + ، Cu2 + Zn2 + , Cd2+للحصول على معقدات فلزية بأشكال هندسية مختلفة. تم الاستدلال عن تكوين معقدات قاعدة شيف وأيضًا قاعدة شيف الأصلية باستخدام كروماتوغرافيا السائل-مطياف الكتلة التي تتفق مع الكتلة المولية التي تم الحصول عليها نظريا، أثبت دراسات مطيافية الاشعة تحت الحمراءحدوث التناسق من خلال N من azobenzene و اوكسجين مجموعة ال OH من خلال ملاحظة الانزياح في قمةazomethines والظهور كل من قمتيM-N و N-O. علاوة على ذلك ، يمكننا أيضًا أن نكتشف بواسطة هذا الجهاز وجود جزيء ماء داخل مجال التناسق. كشفت أطياف UV-Vis لجميع النتائج عن حدوث تناسق من خلال ملاحظة الانزياح في الانتقالات الإلكترونية التي حدثت في الليكاند في المنطقة فوق البنفسجية. تثبت قياسات TGA و DSC لكل من الليكاند و معقد النيكل أيضًا تكون المعقد ووجود جزيء ماء داخل مجال التناسق. بالإضافة إلى ذلك ، كانت نتائج التوصيلية المولارية و الامتصاص الذري اللهبي FAA أقرب إلى نتائج المحسوبة نظريا. أعطت نتائج التشخيص معقدات أحادية النواة وسلوك ثنائي السن واشكال هندسية رباعي السطوح لجميع المعقدات. اعتمادا على خاصية المضادات الحيوية لقاعدة شيف ومعقداتها ، قمنا بدراسة الفعالية الحيوية لقاعدة شف ومعقداتها كما مفصل في المخطوطة.

Charging behavior of ZnMn2O4 and LiMn2O4 in a zinc- and lithium-ion battery: an ab initio study

In the field of sustainable energy storage systems, zinc-ion batteries (ZIB) employing aqueous electrolytes have emerged as viable successors to the widely used lithium-ion batteries, attributed to their cost-effectiveness, environmental friendliness, and intrinsic safety features. Despite these advantages, the performance of ZIBs is significantly hindered by the scarcity of suitable cathode materials, positioning manganese zinc oxide (ZnMn2O4) as a potential solution. In this study, we describe the ZnMn2O4 (ZMO) compound focusing on its properties variations during Zn extraction and potential battery applications. For the sake of comparison, we also analyze the same properties of the LiMn2O4 in its tetragonal phase (TLMO), for the first time, motivated by a recent discovery that the substitution of Zn ions by Li in ZMO forms isostructural TLMO compound at room temperature. The study was conducted within the density functional theory (DFT) framework, where the structural, electronic, magnetic, electrochemical, and spectroscopic properties of ZMO and TLMO are investigated under various conditions. Although both systems crystallize in tetragonal structures, they demonstrate distinct electronic and magnetic properties due to different oxidation states of the Mn. Computationally optimized lattice parameters align closely with experimental values. The TLMO exhibits a narrower band gap compared to ZMO, indicating enhanced electrical conductivity. In addition, TLMO presented a lower diffusion energy barrier than ZMO, indicating better ionic conductivity. To evaluate the potential application of these materials in battery technologies, we further explored their volume changes during charging/discharging cycles, simulating Zn or Li ions extraction. TLMO underwent a significant volume contraction of 5.8% upon complete Li removal, while ZMO experienced a more pronounced contraction of 12.5% with full Zn removal. By adjusting ion extraction levels, it is possible to reduce these contractions, thereby approaching more viable battery applications. Voltage profiles, constructed from DFT-based simulation results, unveiled an average voltage of 4.05 V for TLMO, closely matching experimental values. Furthermore, spectroscopy results provide insights into the electronic transitions and validate the computational findings, consolidating our understanding of the intrinsic properties of ZMO and TLMO.

Simulation of electron transport in a catoptric photomultiplier tube concept for large rectangular scintillator crystals

Spectroscopic scintillation detector form factors have been guided primarily by the design of commercially available photonic sensors. These devices, such as photomultiplier tubes, silicon photomultipliers, and hybrid photodetectors have underperformed in one or more areas such as size, power consumption, and resolution. A novel photomultiplier tube having a 50.8×152.4 mm2 rectangular window, utilizing a reflection-mode photocathode, and a low-gain, miniaturized dynode set is considered here to improve photosensor packaging while enabling high-efficiency, low-resolution scintillation spectroscopy with large, planar scintillators. Using a phenomenological multiphysics simulation process informed by empirical data, photoelectron collection efficiency, single-photoelectron response, electron transit time, and transit time spread have been modeled over a range of operating potentials. At 750 V between the photocathode and anode, 72.5% of photoelectrons are collected at the first dynode, and the average gain is estimated to be 805. The most probable transit time is 14.9 ns, with a transit time spread of 2.7 ns full-width at half-maximum.

Numerical calculation of the probability of an electronic transition in a two-barrier heterostructure by a thin nanolayer

Numerical calculation of the probability of an electronic transition in a two-barrier heterostructure by a thin nanolayer

Unveiling the Structural and Optical Properties of Samarium Titanates Pyrochlore, Sm2Ti2O7

A magnetic system whose geometry prevents all pairwise spin interactions from being fulfilled simultaneously to minimize the energy is said to be frustrated. These systems are prevalent throughout all disciplines of physical and chemical study. This article reports a detailed structural and optical analysis of such frustrated Sm2Ti2O7 (STO), a pyrochlore structure. The ordered pyrochlore, STO of cubic symmetry, space group Fd3¯m [no. 227], has been synthesized using the standard solid-state reaction method. The Tauc’s plot reveals a direct band gap value of 3.8 eV from ultraviolet-visible reflectance data. Photoluminescence studies for STO using 280 nm excitation wavelength show the most intense emission peak at 395 nm, 468 nm, and other weak emissions at 368 nm, 412 nm, 430 nm, 449 nm, and 514 nm corresponding to the respective electronic transitions, indicates that the materials show photoluminescence properties. However, the unique characteristics of Sm2Ti2O7, including its wide band gap, photoluminescence, and high refractive index, make it a promising candidate for various magneto-optical, solid oxide fuel cell device fabrication applications.

Impact of T i/T e ratio on ion transport based on EAST H-mode plasmas

At the EAST tokamak, the ion temperature (T i) is observed to be clamped around 1.25 keV in electron cyclotron resonance (ECR)-heated plasmas, even at core electron temperatures up to 10 keV (depending on the ECR heating power and the plasma density). This clamping results from the lack of direct ion heating and high levels of turbulence-driven transport. Turbulent transport analysis shows that trapped electron mode and electron temperature gradient-driven modes are the most unstable modes in the core of ECR-heated H-mode plasmas. Nevertheless, recently it was found that the T i/T e ratio can increase further with the fraction of the neutral beam injection (NBI) power, which leads to a higher core ion temperature (T i0). In NBI heating-dominant H-mode plasmas, the ion temperature gradient-driven modes become the most unstable modes. Furthermore, a strong and broad internal transport barrier (ITB) can form at the plasma core in high-power NBI-heated H-mode plasmas when the T i/T e ratio approaches ~1, which results in steep core T e and T i profiles, as well as a peaked n e profile. Power balance analysis shows a weaker T e profile stiffness after the formation of ITBs in the core plasma region, where T i clamping is broken, and the core T i can increase further above 2 keV, which is 80% higher than the value of T i clamping in ECR-heated plasmas. This finding proposes a possible solution to the problem of T i clamping on EAST and demonstrates an advanced operational regime with the formation of a strong and broad ITB for future fusion plasmas dominated by electron heating.

Insights on Z-scheme interfacial charge transfer of TiO2-NRAs/BiOI-NFs/Au-NPs nanoheterostructures and unveiling enhanced photoelectrochemical performances

We synthesized TiO2-NRAs/BiOI-NFs/Au-NPs ternary Z-scheme nanoheterostructure using an accessible preparation method. The ternary nanoheterostructureexhibited enhanced photoelectrochemical (PEC) performance compared to other binary nanoheterostructure. The improved performance was attributed to the synergistic effect between enhanced charge separation and improved injection efficiency. An interfacial charge migration mechanism involving plasmon-induced hot electron injection and transition with oxygen vacancies defects was proposed. The triple nanohybrids showed a higher photodegradation rate for methyl orange (MO). Based on the scheme, the TiO2-NRAs/BiOI-NFs/Au-NPs ternary nanohybrids exhibited a photodegradation rate of 96.6% toward degradation of MO irradiated by UV-visible light, 1.47 and 1.19 fold that of BiOI-NFs/Au-NPs and TiO2-NRAs/BiOI-NFs, respectively. Furthermore, the TiO2-NRAs/BiOI-NFs/Au-NPs ternary nanoheterojunction exhibits the best photodegradation performance under near-infrared light irradiation, with a photodegradation rate 4.3 times and 1.2 times that of the binary TiO2-NRAs/BiOI-NFs and BiOI-NFs/Au-NPs nanoheterojunction composites, respectively. These findings provide insights into interfacial charge transfer in TiO2-NRAs/BiOI-NFs/Au-NPs nanoheterostructures and demonstrate their enhanced PEC performances, inspiring the design of high-efficiency and non-toxic Z-scheme heterostructures for various applications.

Synthesis, NMR, electronic properties using DFT study and anticancer activity of 3-methyl-6-(m-tolylamine) quinazolin-4(3H)-one

3-methyl-6-(m-tolylamine) quinazolin-4(3H)-one (MTAQ) was synthesized. Its formation was ascertained with the help ESI mass spectroscopy in conjunction with 1HNMR spectroscopy. Anticancer activity of MTAQ was measured experimentally, for human carcinoma cell line pertaining to cervix (HeLa). Optimized structure parameters, Frontier molecular orbital (FMO) behavior, non linear optical (NLO) profile, molecular electrostatic potential surface (MESP), Fukui functions (FF) and thermodynamic parameters were evaluated for the molecule of interest employing DFT/B3LYP/6–311++G(d,p) formalism. TD-DFT was made use of to calculate absorption maxima (λmax) of electronic transitions for the molecule in CDCl3 solvent. Frontier molecular orbitals revealed the origin of UV–Vis spectrum and to comprehend chemical reactivity of the molecule. Good coincidence was noticed between measured and computed structure parameters, UV–Vis spectra, and 1HNMR signals. Fukui functions helped in identifying electrophilic and nucleophilic centers of MTAQ. The calculations showed that MTAQ exhibits significant NLO activity in addition to predicting existence of intramolecular hydrogen bond.

Adjustable n→π* electronic transition by sulfonated benzene functionalized g-C3N4 for enhanced photocatalytic H2 generation

The photocatalytic efficiency of graphitic carbon nitride (g-C3N4) in hydrogen production is primarily hindered by its poor absorption of visible light, rapid recombination of electron-hole pairs, and the absence of hydroxyl radical formation. Herein, a novel g-C3N4 nanosheets functionalized with sulfonic acid groups were effectively produced through thermal polymerization of melamine and 2, 4-diamino-6-phenyl-1, 3, 5-triazine (DPT), followed by sulfonation treatment. The introduction of the phenyl group brings about alterations to the initial symmetrical arrangement of g-C3N4, leading to the disruption of certain hydrogen bonds. This, in turn, facilitates the movement of electrons from the n to π* orbitals, resulting in enhanced light absorption and improved efficiency in charge separation. Moreover, it induces modifications to the band structure and amplifies the production of hydroxyl radicals. Additionally, the introduction of sulfonic acid enhances the water affinity and the ability of dispersing graphitic carbon nitride in water. The optimized sulfonated benzene-substituted g-C3N4 (1000-BCN-SO3H) with a melamine to DPT ratio of 4:1 exhibits a maximum hydrogen production rate of 6.52 mmol·h−1·g−1 under simulated sunlight irradiation with good cycling stability, which is 3.93 times higher than that of g-C3N4 nanosheets. This research offers a promising opportunity for a novel approach in advancing carbon nitride materials for effective photocatalytic processes.

Study on ESIPT process of fluorescence probe BT-ITC for detecting H2S in DMF/H2O mixed solution

A probe molecule named BT-ITC with an isothiocyanate group was synthesized and evaluated for its H2S sensing ability based on the excited state intramolecular proton transfer (ESIPT) process J K Kim, S Y Bong, R Park, J Park, D Ok Jang 2022 An ESIPT-based fluorescent turn-on probe with isothiocyanate for detecting hydrogen sulfide in environmental and biological systems, Spectrochimica Acta Part A 278 121333. The BT-ITC molecule has a large Stokes shift, short response time, and low detection limit. The end result of the reaction between the molecules BT-ITC and H2S is the BTC-NH2 molecule. The hydrogen bond of the Enol structure BTC-NH2 molecule in excited-state (S1 state) is strengthened, compared to the ground-state (S0 state). The calculated absorption and fluorescence spectra were in good agreement with the experimental values. The frontier molecule orbitals (FMOs), the potential energy curve (PEC), and scatter plots of reduced density gradient (RDG) were calculated. According to aforementioned, it was discovered that the charges of BTC-NH2 molecule were rearranged via an electron transition brought on by photoexcitation. This changes the acidity and alkaline of the proton donor and acceptor, and thus promotes the ESIPT process.

Resonant Raman scattering of few layers CrBr3

We investigate the vibrational and magnetic properties of thin layers of chromium tribromide (CrBr3) with a thickness ranging from three to twenty layers (3–20 L) revealed by the Raman scattering (RS) technique. Systematic dependence of the RS process efficiency on the energy of the laser excitation is explored for four different excitation energies: 1.96 eV, 2.21 eV, 2.41 eV, and 3.06 eV. Our characterization demonstrates that for 12 L CrBr3, 3.06 eV excitation could be considered resonant with interband electronic transitions due to the enhanced intensity of the Raman-active scattering resonances and the qualitative change in the Raman spectra. Polarization-resolved RS measurements for 12 L CrBr3 and first-principles calculations allow us to identify five observable phonon modes characterized by distinct symmetries, classified as the Ag\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\ ext {g}$$\\end{document} and Eg\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\ ext {g}$$\\end{document} modes. The evolution of phonon modes with temperature for a 16 L CrBr3 encapsulated in hexagonal boron nitride flakes demonstrates alterations of phonon energies and/or linewidths of resonances indicative of a transition between the paramagnetic and ferromagnetic state at Curie temperature (TC≈50\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_\ ext {C} \\approx 50$$\\end{document} K). The exploration of the effects of thickness on the phonon energies demonstrated small variations pronounces exclusively for the thinnest layers in the vicinity of 3–5 L. We propose that this observation can be due to the strong localization in the real space of interband electronic excitations, limiting the effects of confinement for resonantly excited Raman modes to atomically thin layers.

Intermolecular interaction of azide, cyano and alkyne-N-phenethylacetamide dimers: Experimental and quantum chemical approach

In this study, we present the synthesis and structure characterization by single-crystal X-ray Diffraction (SC-XRD), Ultraviolet Spectroscopy (UV), Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR) and High-resolution Mass Spectrometry (HRMS) of 2-azido-N-phenethylacetamide (4) and 2-cyano-N-phenethylacetamide (6). Further, Density Functional Theory (DFT) was employed to get a better insight regarding the properties exhibited by the compounds. The computational chemistry has been used to explain and investigate the bimolecular nucleophilic substitution (SN2) and concerted acyl substitution mechanisms for the synthesis of compounds 4 and 6, respectively. Additionally, intrinsic reaction coordinate (IRC) calculations confirm the transition state for these reactions. The X-ray diffraction analysis showed that the compounds 4 and 6 crystallized as monoclinic systems, in space group P21/c and P21/n, respectively. The Hirshfeld Surface Analysis revealed that the main contributions in the crystal packing have H···H, H···N/N···H, H···C/C···H and H···O/O···H interactions. The frontier molecular orbital energies were calculated and the HOMO-LUMO energy gap of 4 and 6 were 10.011 and 10.278 eV, respectively. Theoretical values of electronic transitions, vibrational frequencies and NMR chemical shifts were calculated and compared with experimental results, they all showed good results.

Dual-comb spectroscopy in the deep ultraviolet

This Letter reports dual-frequency-comb spectroscopy in the deep ultraviolet used to characterize transient laser-produced plasmas. Dual-comb spectroscopy at these wavelengths enables access to a large number of strong electronic transitions in neutral and ionized atoms and molecules. This broadband dual-frequency-comb system at 265 nm measures multiple transitions in neutral and singly ionized iron atoms in a laser-produced plasma. Analysis of absorption spectra yields time-resolved ion and neutral column densities, excitation temperatures, and electron densities, which are measured down to 1014cm−3 levels. The results provide insights into low-temperature plasma properties.

Density Functional Theory Study of the Spin-Orbit Insulating Phase in SnTe Cubic Nanowires: Implications for Topological Electronics.

We investigate the electronic, structural, and topological properties of the SnTe and PbTe cubic nanowires using ab initio calculations. Using standard and linear-scale density functional theory, we go from the ultrathin limit up to the nanowire thicknesses observed experimentally. Finite-size effects in the ultrathin limit produce an electric quadrupole and associated structural distortions; these distortions increase the band gap, but they get reduced with the size of the nanowires and become less and less relevant. Ultrathin SnTe cubic nanowires are trivial band gap insulators; we demonstrate that by increasing the thickness, there is an electronic transition to a spin-orbit insulating phase due to trivial surface states in the regime of thin nanowires. These trivial surface states with a spin-orbit gap of a few meV appear at the same k-point of the topological surface states. Going to the limit of thick nanowires, we should observe the transition to the topological crystalline insulator phase with the presence of two massive surface Dirac fermions hybridized with the persistent trivial surface states. Therefore, we have the copresence of massive Dirac surface states and trivial surface states close to the Fermi level in the same region of the k-space. According to our estimation, the cubic SnTe nanowires are trivial insulators below the critical thickness tc1 = 10 nm, and they become spin-orbit insulators between tc1 = 10 nm and tc2 = 17 nm, while they transit to the topological phase above the critical thickness of tc2 = 17 nm. These critical thickness values are in the range of typical experimental thicknesses, making the thickness a relevant parameter for the synthesis of topological cubic nanowires. Pb1-xSnxTe nanowires would have both these critical thicknesses tc1 and tc2 at larger values depending on the doping concentration. We discuss the limitations of density functional theory in the context of topological nanowires and the consequences of our results on topological electronics.

Enhancement of Photostability Ageing of Samarium Complexes in PMMA Films

AbstractIn this study, a set of β‐diketonate samarium(III) complexes–namely, [Sm(TTA)3Phen], [Sm(TTA)3DPEPO], [Sm(TTA)3Bipy], and [Sm(TTA)3Pyra]–has been synthesized and comprehensively characterized. Upon excitation, these complexes exhibit distinct emissions at 566 nm, 610 nm, 650 nm, and 710 nm, respectively, corresponding to the electronic transitions 4G5/2→6H5/2, 4G5/2→6H7/2, 4G5/2→6H9/2, and 4G5/2→6H11/2. Notably, the most pronounced pinkish‐red emission is associated with the peak at 650 nm. Furthermore, the [Sm(TTA)3DPEPO] complex displays a remarkable photoluminescence quantum yield, reaching up to 15.77 % in a PMMA film matrix. The investigation also involved a prolonged examination lasting over 1200 hours, during which PMMA films doped with the samarium complexes were subjected to humidity and weather conditions to evaluate their photoluminescence stability. The results indicate consistent emissions throughout the humidity test, with an eventual cessation after 1200 hours–except in the case of [Sm(TTA)3Phen] under weather conditions. The enduring emission in this scenario is attributed to the robustness of the phenanthroline ligand, thus highlighting its role in enhancing the durability of the complex.

Topological extension including quantum jump

Non-Hermitian (NH) systems and the Lindblad form master equation have always been regarded as reliable tools in dissipative modeling. Intriguingly, existing literature often obtains an equivalent NH Hamiltonian by neglecting the quantum jumping terms in the master equation. However, there lacks investigation into the effects of discarded terms as well as the unified connection between these two approaches. In this study, we study the Su–Schrieffer–Heeger model with collective loss and gain from a topological perspective. When the system undergoes no quantum jump events, the corresponding shape matrix exhibits the same topological properties in contrast to the traditional NH theory. Conversely, the occurrence of quantum jumps can result in a shift in the positions of the phase transition. Our study provides a qualitative analysis of the impact of quantum jumping terms and reveals their unique role in quantum systems.

Exploring 4-chloro chalcone: Synthesis, spectroscopic, chemical reactivity, topological, hirshfeld surface, drug-Likeness, molecular docking and assessment of electronic properties in diverse solvents

Chalcones are a significant class of naturally occurring chemical substances and their derivatives are extremely influential in the field of biological industries. In the current study, the title composite,4 - Chlorochalcone has undergone extensive investigation to understand its spectral properties using a combination of experimental and theoretical calculations. Fourier transform (FT-IR) infrared and FT-Raman characterizations provided valuable insights into the vibrational assignments (functional groups) in the header molecule, while ultraviolet–visible (UV–Vis) spectroscopy explored its electronic transitions and absorbance characteristics. The electronic properties were studied for the solvents viz., ethanol, methanol, DMSO, acetonitrile and benzene through theoretical-computational DFT calculations, revealing details about their molecular orbitals, electronic energies, and other energy parameters. Additionally, the NBO-natural bond orbital analysis shed light on the chemical bonding and electron distributions by donor and acceptor atoms. Furthermore, MEP- molecular electrostatic potential was analyzed for the various solvents and the calculated energy parameters were obtained. A drug-likeness evaluation was performed to assess its potential as a drug candidate based on its molecular properties. Moreover, the topological analysis and electron-hole distributions, contributed to a comprehensive understanding of electron density and localization within the molecule for the solvents viz., ethanol, methanol, DMSO, acetonitrile and benzene. Molecular docking investigations, as well as the Ramchandran plots, revealed that substituents targeting amino acids contribute to the antiviral action of the header compound. The potential of 4′-Chlorochalcone (ligand) as an antiviral agent offers promising prospects for further exploration and development in various therapeutic areas within the field of medicinal chemistry.

Energy Transfer and Exciton Relaxation in B880-B800-RC Complex through Two-Dimensional Electronic Spectroscopy.

The light-harvesting (LH) and reaction center (RC) core complex of purple bacterium Roseiflexus castenholzii, B880-B800-RC, are different from those of the typical photosynthetic unit, (B850-B800)x-B880-RC. To investigate the excitation flowing dynamics in this unique complex, two-dimensional electronic spectroscopy is employed. The obtained time constants for the exciton relaxation in B880, exciton relaxation in B800, B800 → B880 energy transfer (EET), and B880 → closed RC EET are 43 fs, 177 fs, 1.9 ps, and 205 ps, respectively. These time constants result in an overall EET efficiency similar to that of the typical photosynthetic unit. Analysis of the oscillatory signals reveals that while several vibronic coherences are involved in the exciton relaxation process, only one prominent vibronic coherence, with a frequency of 27 cm-1 and coupled to the B880 electronic transition, may contribute to the B800 → B880 EET process.

Sub-50 fs Formation of Charge Transfer States Rules the Fate of Photoexcitations in Eumelanin-Like Materials.

Eumelanins play a crucial role as photoprotective agents for living organisms, yet the nature of the stationary and transient species involved in the light absorption and deactivation processes remains controversial. Moreover, the critical sub-100 fs time scale, which is key to the characterization of the primary excited species, has remained unexplored. Here, we study the eumelanin analogue polydopamine (PDA) and employ a combination of steady-state and transient optical spectroscopies to reveal the presence of spectrally broad coupled electronic transitions with, at least partial, charge-transfer (CT) character. We monitor the CT state dynamics using tunable sub-20 fs pulses. We find that high photon energy excitation results in accelerated (sub-20 fs) CT formation times while activating pathways, which lead to long-lived (≫1 ns), possibly reactive CT species. On the other hand, visible light excitation results in a slower (≈45 fs) formation of bound CT states, which, however, recombine on the ultrafast sub-2 ps time scale.

Martensitic-like microstructures across the isostructural phase transitions in Cerium

The isostructural gamma–alpha phase transition in elemental cerium is an electronic transition caused by a delocalization of the 4f electrons. This affects the bonding properties of Ce atoms and leads to a large volume collapse reaching ∼17% in the low pressure regime (¡ 2 GPa). While great attention has been drawn on the electronic description of this transition, attempts to understand the mesoscale mechanisms of this structural transition and their consequences in terms of microstructure remain scarce. We have investigated this transition by means of combined X-ray Computed Tomography and Energy Dispersive X-ray Diffraction on polycrystalline samples. Our experimental observations reveal a platelet-shape microstructure across the transition and up to the critical point, which have been associated to displacive mechanisms. Based on continuum mechanics modeling and ab initio calculations, we propose that here, this microstructure is initiated by elastic instability and shear anisotropy in the ¡100¿ directions.