Electronic Transitions Research Articles

Excitation-Wavelength-Dependent Photophysics of a Torsionally Disordered Push-Pull Dye.

The torsional disorder of conjugated dyes in the electronic ground state can lead to inhomogeneous broadening of the S1 ←S0 absorption band, allowing for the selective photoexcitation of molecules with different amounts of distortion. Here, we investigate how this affects electronic transitions to upper excited states. We show that torsion of a core-alkynylated push-pull dye can have opposite effects on the oscillator strength of its lowest-energy transitions. Consequently, photoselection of planar and twisted molecules can be achieved by exciting in distinct absorption bands. Whereas this has limited effect in liquids due to fast planarization of the excited molecules, it strongly affects the overall photophysics in a polymeric environment, where torsional motion is hindered, allowing for the photoselection of molecules with different fluorescence quantum yields and intersystem-crossing dynamics.

Electronic dynamics through conical intersections via non-Markovian stochastic Schrödinger equation with complex modes.

Conical intersections (CIs) play a crucial role in photochemical reactions, offering an efficient channel for ultrafast non-adiabatic relaxation of excited states. This significantly influences the reaction pathways and the resulting products. In this work, we utilize the non-Markovian stochastic Schrödinger equation with complex modes method to explore the dynamics of electronic transitions through conical intersections (CIs) in pyrazine. The linear vibronic coupling model serves as the foundational framework, incorporating both intra-state and inter-state electron-vibrational interactions. The dynamics of the excited electronic transitions are analyzed across varying strengths of system-bath coupling and different bath relaxation times. The accuracy of this method is demonstrated by comparing its predictions with those from the hierarchical equations of motion method.

Combined Experimental and Theoretical Investigation of the Electrochemical Behavior of Hydroxy‐Substituted Anils

AbstractThe present work explored the electrochemical behavior of two organic compounds, o‐hydroxybenzylidene‐orthochloroaniline(Anil‐1) and o‐hydroxynaphthalidene‐orthochloro aniline(Anil‐2) through a series of theoretical and experimental investigations. The vibrational frequencies of two anilswere analyzed experimentally by FTIR and theoretically by DFT studies. A comparison of the frequencies with their unsubstituted analog, o‐hydroxybenzylideneaniline, confirmed the electron‐donating nature of the −Cl and −OH substituents in anils. The hyperconjugative interaction energy obtained from NBO analysis divulged the direction of the electron donation from the donor orbitals to the acceptor orbitals. UV‐visible studies illustrated prominent π→π* electronic transitions with significant oscillator strength(0.10–0.26) and molar extinction coefficient(~104) experimentally. Analysis of the global and local reactive descriptors of anils revealed a lower HOMO‐LUMO energy gap of Anil‐2(4.05 eV) than Anil‐1(4.46 eV), corroborating the order of decreasing reactivity to be Anil‐2>Anil‐1. The Cyclic Voltammetry studies disclosed the involvement of an oxidation process in Anil‐1 and Anil‐2 with a higher oxidation potential of Anil‐1 (1.43 V) than Anil‐2(1.31 V) due to the naphthyl moiety of the latter. However, the absence of a cathodic peak in both cases envisaged the irreversible nature of oxidation. The results demonstrated that both the anils could be suitable optical materials for microelectronics applications.

A comprehensive study on three typical photoacid generators using photoelectron spectroscopy and abinitio calculations.

Conducting a comprehensive molecular-level evaluation of a photoacid generator (PAG) and its subsequent impact on lithography performance can facilitate the rational design of a promising 193nm photoresist tailored to specific requirements. In this study, we integrated spectroscopy and computational techniques to meticulously investigate the pivotal factors of three prototypical PAG anions, p-toluenesulfonate (pTS-), 2-(trifluoromethyl)benzene-1-sulfonate (TFMBS-), and triflate (TF-), in the lithography process. Our findings reveal a significant redshift in the absorption spectra caused by specific PAG anions, attributed to their involvement in electronic transition processes, thereby enhancing the transparency of the standard PAG cation, triphenylsulfonium (TPS+), particularly at ∼193nm. Furthermore, the electronic stability of PAG anions can be enhanced by solvent effects with varying degrees of strength. We observed the lowest vertical detachment energy of 6.6eV of pTS- in PGMEA solution based on the polarizable continuum model, which prevents anion loss at 193nm lithography. In addition, our findings indicate gas-phase proton affinity values of 316.4 kcal/mol for pTS-, 308.1 kcal/mol for TFMBS-, and 303.2 kcal/mol for TF-, which suggest the increasing acidity strength, yet even the weakest acid pTS- is still stronger than strong acid HBr. The photolysis of TPS+-based PAG, TPS+·pTS-, generated an excited state leading to homolysis bond cleavage with the lowest reaction energy of 83 kcal/mol. Overall, the PAG anion pTS- displayed moderate acidity, possessed the lowest photolysis reaction energy, and demonstrated an appropriate redshift. These properties collectively render it a promising candidate for an effective acid producer.

X-ray Circular Dichroism measured by cross-polarization X-ray Transient Grating

Abstract Measuring natural circular dichroism in the X-ray regime to extract stereochemical information from chiral molecules in solution remains a challenge. This is primarily due to technical limitations of the existing synchrotron sources. It hinders access to measurements of local chirality by exploiting core hole electronic transitions. In response to this challenge, we propose an alternative approach: utilizing XFEL-based cross-polarization X-ray Transient Grating (XTG). This method provides an indirect means to measure X-ray Circular Dichroism (XCD). Notably, our findings reveal that the signal only emerges once the excited cores have undergone dephasing through relaxation. XTG is now routinely measured in the XUV regime, and has recently been made available for hard X-rays. Free electron lasers now offer polarization controls and XTG can be extended to various polarization states for the two pump beams, making XCD measured by XTG feasible at the current state of the art.

Collective rovibronic dynamics of a diatomic gas coupled by cavity

We consider an ensemble of homonuclear diatomic molecules coupled to the two polarization directions of a Fabry-Pérot cavity via fully quantum simulations. Accompanied by analytical results, we identify a coupling mechanism mediated simultaneously by the two perpendicular polarizations, and inducing polaritonic relaxation towards molecular rotations. This mechanism is related to the concept of light-induced conical intersections (LICIs). However, unlike LICIs, these nonadiabatic pathways are of a collective nature, since they depend on the intermolecular orientation of all electronic transition dipoles in the polarization plane. Notably, this rotational mechanism directly couples the bright upper and lower polaritonic states, and it stays in direct competition with the collective relaxation towards dark states. Published by the American Physical Society 2024

Improving Photophysical Properties of Deazaflavin Derivatives by Acrylaldehyde Bridging: A Theoretical Investigation

AbstractThe electronic structure and photophysical properties of several acrylaldehyde‐bridged deazaflavin derivatives (cFLs) were investigated theoretically. The impact of acrylaldehyde bridging on photophysical properties of deazaflavin (cFL) is strongly site‐dependent. Specifically, the change of adiabatic energy of electronic transitions(ΔEad) and vibronic coupling promote fluorescent emission to be comparable to internal conversion of cFL and cFL4 (both C5−C6 and C9−N10 bridged, but C9−N10 bridged by propene), turning them eligible as fluorescent sensors. As El‐Sayed's rule is satisfied in cFL1(C5−C6 bridged), cFL2(C9−N10 bridged) and cFL3(both C5−C6 and C9−N10 bridged), intersystem crossing from first singlet excited state to triplet excited states (Tn) become dominant and the evolution of excited cFLs from T1 appears vital. The rate constants of photophysical processes indicate these cFLs are of dominantly high steady state T1 concentration and are potential triplet sensitizers. We expect the findings would pave the way for rational design of novel cFLs with extraordinary photophysical properties.

Transparent Ce3+-doped fluorapatite (FAP) ceramics fabricated by spark plasma sintering (SPS)

Polycrystalline Ce3+-doped fluorapatite (Ce:FAP) transparent ceramics with fine microstructures were fabricated through liquid-phase synthesis for the initial powder and spark plasma sintering (SPS) for full densification. These ceramics were confirmed to have a single-phase crystal structure, and the average grain sizes were determined to be 139 and 135 nm for the 1 and 2 at.% Ce-doping concentrations, respectively. Their emission spectra revealed that the fabricated ceramics convert UV light to visible light emission due to the 5d→4f electronic transition of Ce3+. These ceramics are expected to be useful in photonic applications.

Quantifying Covalency and Environmental Effects in RASSCF-Simulated O K-Edge XANES of Uranyl.

A RASSCF approach to simulate the O K-edge XANES spectra of uranyl is employed, utilizing three models that progressively improve the representation of the local crystal environment. Simulations successfully reproduce the observed three-peak profile of the experimental spectrum and confirm peak assignments made by Denning. The [UO2Cl4]2- model offers the best agreement with experiment, with peak positions (to within 1 eV) and relative peak separations accurately reproduced. Establishing a direct link between a specific electronic transition and peak intensity is complicated, as a large number of possible transitions can contribute to the overall peak profile. Furthermore, a relationship between oxygen character in the antibonding orbital and the strength of the transition breaks down when using a variety of orbital composition approaches at larger excitation energy. Covalency analysis of the U-O bond in both the ground- and excited-state reveals a dependence on the crystal environment. Orbital composition analysis reveals an underestimation of the uranium contribution to ground-state bonding orbitals when probing O K-edge core-excited states, regardless of the uranyl model employed. However, improving the environmental model provides core-excited state electronic structures that are better representative of that of the ground-state, validating their use in the determination of covalency and bonding.

Effect of Dissolved Organic Matter on the Photodegradation of Decachlorobiphenyl (PCB-209) in Heterogeneous Systems: Experimental Analysis and Excited-State Theory Calculations.

Dissolved organic matter (DOM) can affect the transformation of pollutants through photosensitization, but most current research focuses on hydrophilic pollutants, making it such that less attention is paid to hydrophobic pollutants. In this paper, the effect and action mechanism of coexisting DOM on the photodegradation of decachlorobiphenyl (PCB-209) on suspended particles collected from the Yellow River were systematically investigated in a heterogeneous system using DOM standards and model compounds. Through molecular probe experiments, mass spectrometry analysis and theoretical calculations, we found that the excited triplet state of DOM (3DOM*) could excite PCB-209 to undergo dechlorination reaction. Due to the different modes of electron transition, the presence of carbonyl groups decreased the energy of 3DOM*, whereas the electron-donating groups made the energy of 3DOM* higher. DOM containing phenolic hydroxyl groups led to a higher steady-state concentration of •OH, and DOM containing phenyl ketone structures had a stronger ability to produce •O2-. Compared with aqueous •OH, •O2- produced from hydrophobic microregions could react more readily with PCB-209. This study deepens the understanding of the role of different functional groups of DOM in the photosensitized transformation of hydrophobic compounds.

Modeling of the electronic excited states in high-temperature flows

This article introduces a novel model for describing the electronic excited states in the direct simulation Monte Carlo (DSMC) technique. The model involves the coupling the vibrational and electronic modes of molecular species, enabling each electronic excited state to excite its unique vibrational quantum levels. Numerical techniques are developed for equilibrium and post-collision sampling, as well as for measuring the internal temperature. The DSMC results demonstrate excellent agreement with theoretical predictions, providing verification of the successful implementation in a DSMC solver. For important thermophysical properties of molecular oxygen, such as the specific heat capacity, it is shown that the new model provides a better prediction than a compilation of past studies in comparison to the standard uncoupled approach in DSMC. The model is then applied to simulate a canonical nonreactive oxygen hypersonic flow past a cylindrical body. The population distribution of electronic excited states exhibit significant deviation from the standard approach typically used in the coupling between DSMC and radiation transport solvers.

Ballistic Photons, Justification of their Structure and Movement Patterns

Aim: The work relates to the fundamentals of quantum physics and photonics, in particular to the formation of photons in two states: elementary particles and electromagnetic radiation, and the parameters of their structure and motion processes. The study of these problems is a relevant and important task, has not been fully studied. In general case, a photon is considered an elementary particle and wave, quantum of energy emitted by its electromagnetic field, which does not exist without moving at the speed of light. However, the presence of the material part of a photon is not always manifested, so a photon is considered a wave of electromagnetic radiation and the photon has no internal structure and dimensions, except for its wave parameters. The process of photon movement is also problematic. It is believed that it exists as a particle at the moment of its origin, and then it is only the movement of a wave, which, when meeting a target, again turns into an elementary particle. Moreover, ballistic photons is not, and their flight occurs by absorption and re-emission of waves by the environment. However, all these factors have contradictions, the elimination of which is the main goal of the work performed. Its scientific novelty is a new justification for the presence and parameters of a ballistic photon and the processes of its movement on the basis of reliable laws of physics. Methodology: The research methodology is based on the general principles of scientific knowledge, on the application of the laws of dialectics and reliable laws of physics. The author's method was also used – this access to the initial level of the material world, which is formed by physical fields and particles on the basis of natural physical constants: the speed of light c, Planck's constant h, gravitational constant G. New Results of the Work: The possibility of the existence of ballistic photons in the dual form of substance and electromagnetic waves is shown, within the framework of the general physical principles of the existence of elementary particles and the real principles of their movement in the material world. It was found that the disappearance of ballistic photons in flight after their birth and their appearance when meeting a target can be explained by their quantum structure and the process of their movement by quantum jumps based on the Heseisenberg uncertainty principle. Conclusions: The presence of the proposed quantum structure of the photon and the process of its movement is ensured by the absence of contradictions with the real laws of the material world that have a strict physical basis. For to confirm the reality of the existence of ballistic photons in the form of a real quantum mechanical particle, having the shape of a regular hexagon with a side of 1/ 6 of the wavelength λ of their radiation, as well as their movement in quantum jumps at 1/ 6 of the length of this wave, an experiment has been proposed. All laboratories with metrological equipment are invited to conduct the experiment.

Constructing Slip Stacking Diversity in Van der Waals Homobilayers.

The van der Waals (vdW) interface provides two important degrees of freedom-twist and slip-to tune interlayer structures and inspire unique physics. However, constructing diversified high-quality slip stackings (i.e., lattice orientations between layers are parallel with only interlayer sliding) is more challenging than twisted stackings due to angstrom-scale structural discrepancies between different slip stackings, sparsity of thermodynamically stable candidates and insufficient mechanism understanding. Here, using transition metal dichalcogenide (TMD) homobilayers as a model system, this work theoretically elucidates that vdW materials with low lattice symmetry and weak interlayer coupling allow the creation of multifarious thermodynamically advantageous slip stackings, and experimentally achieves13 and 9 slip stackings in 1T″-ReS2 and 1T″-ReSe2 bilayers via direct growth, which are systematically revealed by atomic-resolution scanning transmission electron microscopy (STEM), angle-resolved polarization Raman spectroscopy, and second harmonic generation (SHG) measurements. This work also develops modulation strategies to switch the stacking via grain boundaries (GBs) and to expand the slip stacking library from thermodynamic to kinetically favored structures via in situ thermal treatment. Finally, density functional theory (DFT) calculations suggest a prominent dependence of the pressure-induced electronic band structure transition on stacking configurations. These studies unveil a unique vdW epitaxy and offer a viable means for manipulating interlayer atomic registries.

Integration of Perylene Diimide into a Covalent Organic Framework for Photocatalytic Oxidation.

Perylene diimides (PDIs) have garnered considerable attention due to its immense potential in photocatalysis. However, manipulating the molecular packing within their aggregates and enhancing the efficiency of photogenerated carrier recombination remain significant challenges. In this study, we demonstrate the incorporation of a PDI unit into a covalent organic framework (COF), named PDI-PDA, by linking an ortho-substituted PDI with p-phenylenediamine (PDA) to control its intermolecular aggregation. The incorporation enables precise modulation of electron transfer dynamics, leading to a ten-fold increase in the efficiency of photocatalytic oxidation of thioether to sulfoxide with PDI-PDA compared to the PDI molecular counterpart, achieving yields exceeding 90%. Electron property studies and density functional theory calculations show that the PDI-PDA with its well-defined crystal structure, enhances π-π stacking and lowers the electron transition barrier. Moreover, the strong electron-withdrawing ability of the PDI unit promotes the spatial separation of the valency band maximum and conduction band minimum of PDI-PDA suppressing the rapid recombination of photogenerated electron-hole pairs and improving charge separation efficiency to give high photocatalytic efficiency. This study provides a brief yet effective way for the improvement of the photocatalytic efficiency of commonly used PDI-based dyes by integrating them into a framework skeleton.

Integration of Perylene Diimide into a Covalent Organic Framework for Photocatalytic Oxidation

Perylene diimides (PDIs) have garnered considerable attention due to its immense potential in photocatalysis. However, manipulating the molecular packing within their aggregates and enhancing the efficiency of photogenerated carrier recombination remain significant challenges. In this study, we demonstrate the incorporation of a PDI unit into a covalent organic framework (COF), named PDI‐PDA, by linking an ortho‐substituted PDI with p‐phenylenediamine (PDA) to control its intermolecular aggregation. The incorporation enables precise modulation of electron transfer dynamics, leading to a ten‐fold increase in the efficiency of photocatalytic oxidation of thioether to sulfoxide with PDI‐PDA compared to the PDI molecular counterpart, achieving yields exceeding 90%. Electron property studies and density functional theory calculations show that the PDI‐PDA with its well‐defined crystal structure, enhances π‐π stacking and lowers the electron transition barrier. Moreover, the strong electron‐withdrawing ability of the PDI unit promotes the spatial separation of the valency band maximum and conduction band minimum of PDI‐PDA suppressing the rapid recombination of photogenerated electron‐hole pairs and improving charge separation efficiency to give high photocatalytic efficiency. This study provides a brief yet effective way for the improvement of the photocatalytic efficiency of commonly used PDI‐based dyes by integrating them into a framework skeleton.

Verification and validation of electrostatic turbulence simulation for numerical Lie transform code

Abstract This paper reports the verification and validation of a new gyrokinetic (GK) code, numerical Lie transform (NLT), for electrostatic turbulence simulation in tokamak plasmas. Based on the standard cyclone base case (CBC), NLT has been verified against two typical GK codes, GK toroidal code (GTC) and GK numerical experiment of tokamak, by simulating the ion temperature gradient mode and trapped electron mode. The linear dispersion relation and mode structure agree well among all these codes. In nonlinear simulation, the time evolution of ion heat diffusivity obtained from NLT is consistent with the GTC results. Furthermore, utilizing experimental equilibria with obvious turbulence features from HL-2A shot #22388, the validation of NLT for real tokamak simulation has been carried out. The profiles of ion turbulent thermal diffusivity calculated by NLT match well with experimental results.

From lithium and sodium superoxides to singlet-oxygen - insights into the mechanism of dissociation using SHARC-MD.

The parasitic formation of singlet oxygen in aprotic alkaline/air batteries presents a challenge for the technical development of these systems. Avoidance strategies and investigation of reaction paths such as disproportionation of LiO2 and NaO2 have been presented. Furthermore, the dissociation of these superoxide systems have been discussed be as an alternative reaction channel. Here, we present a fundamental study of the electronic nature and dissociation behaviour of the alkali superoxides. The molecular systems were calculated at the CASSCF/CASPT2-level of theory. We determined the minimum energy crossing points along the dissociation required to form 3O2 and 1O2. Building on these results, a surface-hopping AIMD-simulation was performed employing the SHARC program package to follow the electronic transitions along the minimum energy crossing pooints during the dissociation. The feasibility of populating the electronic state corresponding to the formation of singlet oxygen during dissociation was demonstrated. For LiO2, 6.85% of the trajectories were found to terminate under formation of 1O2, whereas for NaO2 only 1.68% of the trajectories ended up in 1O2 formation. This represents an inverse trend to that reported in the literature. This observation suggests that the dissociation is a viable, monomolecular reaction path to 1O2 that complements the disproportionation pathway.

Synthesis, crystal structure, and DFT studies of NHC mediated Pd-PEPPSI complex: Application for Suzuki reaction

A novel air and moisture resistant Pd-PEPPSI (pyridine-enhanced precatalyst preparation, stabilization, and initiation) complex was synthesized via the reaction of benzimidazolium salt, PdCl2, KBr, K2CO3, and pyridine. The structure was characterized by spectroscopic methods such as 1H and 13C NMR, FT-IR, UV–vis. and single X-ray diffraction techniques. In order to evaluate the synthesized Pd complex in a detailed manner in terms of structural, bonding, electronic, and thermodynamic characteristics, DFT-based calculations were carried out at the B3LYP/6-311++G (d, p)/LANL2TZ theory level. Natural bond orbital (NBO) analysis was implemented to provide more insights about the possible donor-acceptor interactions and types of hybridization. Also, TD-DFT calculations were performed to rationalize the nature of the observed electronic transitions. The complex showed high catalytic activity in the Suzuki–Miyaura cross coupling of aryl chlorides with phenylboronic acid. Aryl chlorides bearing either electron- donating or withdrawing substituents afforded a wide range of biaryl derivatives that were isolated in the range of 55–97 % yields (7 examples). The reactions were carried out at very low catalyst loading (0.25 mol%) in the presence of air using a green water-based solvent (ipr:H2O/ 1:3). The palladium complex was found to be efficient for the coupling of aryl chlorides with arylboronic acids under aerobic conditions, affording the corresponding biaryls in high yields.

Gyrokinetic simulations of the kinetic electron effects on the electrostatic instabilities on the ITER baseline scenario

The linear and nonlinear simulations are carried out using the gyrokinetic code NLT for the electrostatic instabilities in the core region of a deuterium plasma based on the International Thermonuclear Experimental Reactor (ITER) baseline scenario. The kinetic electron effects on the linear frequency and nonlinear transport are studied by adopting the adiabatic electron model and the fully drift-kinetic electron model in the NLT code, respectively. The linear simulations focus on the dependence of linear frequency on the plasma parameters, such as the ion and electron temperature gradients , the density gradient and the ion–electron temperature ratio . Here, is the major radius, and and denote the electron and ion temperatures, respectively. is the gradient scale length, with denoting the density, the ion and electron temperatures, respectively. In the kinetic electron model, the ion temperature gradient (ITG) instability and the trapped electron mode (TEM) dominate in the small and large region, respectively, where is the poloidal wavenumber. The TEM-dominant region becomes wider by increasing (decreasing) ( ) or by decreasing . For the nominal parameters of the ITER baseline scenario, the maximum growth rate of dominant ITG instability in the kinetic electron model is about three times larger than that in the adiabatic electron model. The normalized linear frequency depends on the value of , rather than the value of or , in both the adiabatic and kinetic electron models. The nonlinear simulation results show that the ion heat diffusivity in the kinetic electron model is quite a lot larger than that in the adiabatic electron model, the radial structure is finer and the time oscillation is more rapid. In addition, the magnitude of the fluctuated potential at the saturated stage peaks in the ITG-dominated region, and contributions from the TEM (dominating in the higher region) to the nonlinear transport can be neglected. In the adiabatic electron model, the zonal radial electric field is found to be mainly driven by the turbulent energy flux, and the contribution of turbulent poloidal Reynolds stress is quite small due to the toroidal shielding effect. However, in the kinetic electron model, the turbulent energy flux is not strong enough to drive the zonal radial electric field in the nonlinear saturated stage. The kinetic electron effects on the mechanism of the turbulence-driven zonal radial electric field should be further investigated.

Effect of terminal substituents on intramolecular charge transfer in one- and two-photon absorption of zinc phthalocyanine derivatives

Zinc phthalocyanine derivatives have unique structure and photophysical properties, which make them a remarkable potential in the fields of optoelectronics as well as biomedicine. In order to reveal the effect of the terminal substituents on the electron transition mechanisms, one-photon absorption (OPA) and two-photon absorption (TPA) processes of three zinc phthalocyanines modified with different terminal substituents (PcZn-0, PcZn-1 and PcZn-2) have been analyzed by using density-functional theory (DFT) in combination with the sum-over-states (SOS) model, the visualization of the transition density matrix (TDM) as well as charge density difference (CDD) calculations. Red-shifted OPA absorption peaks with enhanced intensities, have been observed in molecules PcZn-1, PcZn-2 with long terminal substituents. However, for TPA process, a more effective charge transfer over almost the entire molecule has been observed in PcZn-1 molecule with 4-methoxybenonic acid as terminal substituents. When H-atoms in the hydroxyl groups of four terminal 4-Methoxybenzoic acid groups were substituted by dispersed red-one chains, a limited range of intramolecular charge transfer and localized excitation inside the dispersed red-one chain were observed, leading to a localized excitation absorption peak and expanding the wavelength region of TPA response. Furthermore, terminal substituents with conjugated branches exhibit a stronger cooperative effect between the terminal chains and shows larger TPA response. On the contrary, excessive dihedral angles between different groups can weaken the conjugation degree of molecules and affect intramolecular charge transfer as well as TPA response.