Electronic Excitation Energy Research Articles

Theory of photosynthetic membrane influence on B800-B850 energy transfer in the LH2 complex.

Photosynthetic organisms rely on a network of light-harvesting protein-pigment complexes to efficiently absorb sunlight and transfer excitation energy to reaction centre proteins where charge separation occurs. In photosynthetic purple bacteria, these complexes are embedded within the cell membrane, with lipid composition affecting complex clustering, thereby impacting inter-complex energy transfer. However, the impact of the lipid bilayer on intra-complex excitation dynamics is less understood. Recent experiments have addressed this question by comparing photo-excitation dynamics in detergent-isolated light-harvesting complex 2 (LH2) to LH2 complexes embedded in membrane discs mimicking the biological environment, revealing differences in spectra and energy transfer rates. In this paper, we use available quantum chemical and spectroscopy data to develop a complementary theoretical study on the excitonic structure and intra-complex energy transfer kinetics of the LH2 of photosynthetic purple bacteria Rhodoblastus (Rbl.) acidophilus (formerly Rhodopseudomonas acidophila) in two different conditions: the LH2 in a membrane environment and detergent-isolated LH2. We find that dark excitonic states, crucial for B800-B850 energy transfer within LH2, are more delocalised in the membrane model. Using non-perturbative and generalised Förster calculations, we show that such increased quantum delocalisation results in a 30% faster B800 to B850 transfer rate in the membrane model, in agreement with experimental results. We identify the dominant energy transfer pathways in each environment and demonstrate how differences in the B800 to B850 transfer rate arise from changes in LH2's electronic properties when embedded in the membrane. Furthermore, by accounting for the quasi-static variations of electronic excitation energies in the LH2, we show that the broadening of the distribution of the B800-B850 transfer rates is affected by the lipid composition. We argue that such variation in broadening could be a signature of a speed-accuracy trade-off, commonly seen in biological process.

Two-photon absorption of BODIPY, BIDIPY, GADIPY, and SBDIPY.

Substituted boron-dipyrromethene compounds (BODIPYs) have gained significant attention due to their tunable photophysical properties, including two-photon absorption (2PA), a nonlinear optical process where two photons are absorbed simultaneously. The tuning of BODIPY's photophysical properties has recently led to the synthesis of pnictogen-containing derivatives, such as SBDIPY and BIDIPY, where boron is replaced by antimony (Sb) or bismuth (Bi), respectively, as well as other analogues like GADIPY, which contain gallium (Ga). This study presents a computational investigation into their 2PA properties, exploring the impact of various substitutions across these systems. The 2PA cross-sections (σ2PA), electronic excitation energies (ΔE), and dipole moments (μ00, μ11, μ01, Δμ) were computed for 18 DIPY chromophores in the gas-phase with time-dependent density-functional theory (TD-DFT) using several functionals (CAM-B3LYP, ωB97X, M06-2X, M11, and MN15), and then compared to second-order approximate coupled-cluster with the resolution-of-identity approximation (RI-CC2) results. The computed mean absolute errors were small, with the MN15, CAM-B3LYP, and M06-2X functionals being among the best-performing for the properties analyzed. In general, for the parent (unsubstituted) compounds, replacing the core atom in DIPY chromophores results in negligible changes to their σ2PA. However, extending the conjugation through the addition of phenyl substituents significantly increases σ2PA values, and the nature of the core atom impacts the magnitude of this enhancement.

Distinct Effects of Selective Sn Doping at A or B Sites in BaTiO3

The effects of selectively doping Sn into the A‐site or B‐site of BaTiO3 on its crystal structure and electronic and optical properties are systematically evaluated using first‐principles calculations, leading to several intriguing conclusions. After doping Sn at the A‐site, impurity bands originating from Sn are generated, which alter the direct bandgap to an indirect one and decrease the bandgap value, thereby reducing the electron excitation energy required. Meanwhile, (Ba0.875Sn0.125)TiO3 (A‐site) exhibits p‐type semiconductor characteristics with holes as carriers, which is beneficial for enhancing the conductivity of BaTiO3. The introduction of Sn–O interactions through A‐site Sn doping reduces the density of states of O‐2p near the valence band maximum, enhances the mobility of oxygen ions, and promotes the occurrence of redox reactions. In contrast, when Sn is doped at the B‐site, the bottom of the conduction band shifts toward higher energy levels, leading to a significant increase in the bandgap. In addition, (Ba0.875Sn0.125)TiO3 (A‐site doped) and Ba(Ti0.875Sn0.125)O3 (B‐site doped) exhibit distinct optical behaviors, thereby expanding the optical application range of BaTiO3‐based materials. This study highlights the distinct impacts of Sn doping at the A‐site or the B‐site on the modification of BaTiO3 properties, thereby paving a novel path for designing advanced materials.

Learning Intermolecular Electronic Coupling with Molecular-Orbital-Based Descriptors.

Electronic coupling is the key parameter to determine the rate of intermolecular electron transfer and energy transfer at excited states. When excited states are involved, the couplings are state-specific, as they originate from the interactions between different molecular orbitals (MOs). Based on the MO overlap description of the electron transfer (ET) and excitation energy transfer (EET) couplings taken as the domain knowledge, here we propose a graphic molecular orbital (MO) based descriptor to predict intermolecular electronic couplings. As the MOs are characterized by the spatial distribution of their wave functions, namely, the size and sign of the lobes, we transform the grid points of a MO into two feature vectors containing the quantum and spatial information. Then, inspired by the MO overlap description of the electronic couplings, we build the descriptors by multiplying the vectors for paired MOs. Together with a deep neural network (DNN) model, we learn the couplings of hole transfer (HT), electron transfer (ET), and Dexter energy transfer (DET). For the couplings of naphthalene dimers, high accuracy of learning is achieved by our approach compared with the results from quantum chemical (QC) calculations with a small size of training data. Therefore, the MO-pair-based descriptor shows the ability to characterize MO interaction for the high performance learning of electronic couplings and implies the potential of this strategy for other state-specific properties of excited molecular systems.

Nuclear Quantum Effects Have a Significant Impact on UV/Vis Absorption Spectra of Chromophores in Water

AbstractDespite the broadly acknowledged importance of solvation effects on measured UV/Vis spectra in the context of solvatochromism or chemical reactions in solution, it is still an open challenge to calculate UV/Vis spectra with predictive accuracy. This is particularly true when it comes to the impact of nuclear quantum effects on these experimental observables. In the present work, we calculate the UV/Vis absorption spectrum of indole in aqueous solution with a combination of a correlated wavefunction method for computing electronic excitation energies and enhanced path integral simulations for rigorous sampling of nuclear configurations including the quantum effects in solution. After validating our approach based on gas‐phase benchmarking, we demonstrate that the lineshape of the spectrum measured in aqueous solution is quantitatively recovered, without the application of any shifting, scaling, or broadening, only after including nuclear quantum effects in addition to thermal fluctuations and solvation at ambient conditions. Our findings demonstrate that nuclear quantum effects are “visible” in UV/Vis spectra of chromophores measured in solution even at room temperature and, therefore, that they must be considered computationally to achieve predictive accuracy.

Ultrafast Mapping of Electronic and Nuclear Structure in the Photo Dissociation of Nitrogen Dioxide.

We investigate the photoinduced dissociation reaction of NO2 → NO + O upon electronic excitation of the X̃2A1 (D0) to the Ã2B2 (D1) state by femtosecond X-ray absorption spectroscopy at the nitrogen K-edge. We obtain key insight into the chemical bond breaking event and its associated electronic structural dynamics. Calculations of the photoinduced reaction allow to assign the transient absorption features at time scales of 10-50 fs to wave packet motions in the excited D1 and ground D0 states, followed by the formation of the NO photoproduct with a 255 ± 23 fs time constant. Our analysis shows that there is no direct correlation between the 1s core levels and the electronic ground and excited states transition energies and the bond elongation of NO2, while en route to dissociation toward the NO + O photoproducts, in the transient nitrogen K-edge spectra. However, simulations predict that for a sufficiently short UV pump pulse, the early wave packet dynamics in the D1 electronic excited state occurring within the first 35 fs along the bending and symmetric stretching modes can be directly mapped in the transient X-ray absorption spectra.

Linear Response pCCD-Based Methods: LR-pCCD and LR-pCCD+S Approaches for the Efficient and Reliable Modeling of Excited State Properties.

In this work, we derive working equations for the linear response pair coupled cluster doubles (LR-pCCD) ansatz and its extension to singles (S), LR-pCCD+S. These methods allow us to compute electronic excitation energies and transition dipole moments based on a pCCD reference function. We benchmark the LR-pCCD+S model against the linear response coupled-cluster singles and doubles method for modeling electronic spectra (excitation energies and transition dipole moments) of the BH, H2O, H2CO, and furan molecules. We also analyze the effect of orbital optimization within pCCD on the resulting LR-pCCD+S transition dipole moments and oscillator strengths and perform a statistical error analysis. We show that the LR-pCCD+S method can correctly reproduce the transition dipole moments features, thus representing a reliable and cost-effective alternative to standard, more expensive electronic structure methods for modeling electronic spectra of simple molecules. Specifically, the proposed models require only mean-field-like computational cost, while excited-state properties may approach the CCSD level of accuracy. Moreover, we demonstrate the capability of our model to simulate electronic transitions with non-negligible contributions of double excitations and the electronic spectra of polyenes of various chain lengths, for which standard electronic structure methods perform purely.

Towards machine learning prediction of the fluorescent protein absorption spectra

We demonstrate that machine learning models trained on a set of features obtained from QM/MM molecular dynamic trajectories of fluorescent proteins can be used to predict the chromophore dipole moment variation upon excitation, the quantity related to the electronic excitation energy. Linear regression, gradient boosting, and artificial neural network- based models were considered using cross-validation on the training dataset. Gradient boosting approach proved to be the most accurate for both internal (R2 = 0.77) and external (R2 = 0.7) test sets.

Quantum chemical calculations and molecular docking studies of 5-amino-3-(2,5-dimethoxyphenyl)-1-isonicotinoyl-2,3-dihydro-1H-pyrazole-4-carbonitrile

Abstract The five-membered heterocycle pyrazole has two nitrogen atoms next to each other. Natural items and pharmaceuticals using pyrazole as the nucleus have demonstrated a wide range of biological activity. Medications with pyrazole cores may have better pharmacokinetics and pharmacological effects than medicines with similar heterocyclic rings. This is because the pyrazole core has unique physicochemical properties. In this study, 5-amino-3-(2,5-dimethoxyphenyl)-1-isonicotinoyl-2,3-dihydro-1H-pyrazole-4-carbonitrile is synthesized and characterized by means of spectrum and quantum chemical techniques. Using UV–vis absorption technique, Fourier transform infrared (FT-IR), and Fourier transform Raman (FT-Raman) techniques, the spectroscopic properties were examined. There were two regions visible in the experimental Raman as well as infrared spectra: 4,000–400 cm−1 along with 4,000–100 cm−1. The ideal molecular shape, vibrational frequencies, infrared intensity levels, and scattering from Raman were all assessed using density functional theory. The 13C (carbon) and 1H (proton) chemical shifts of the molecule were determined using nuclear magnetic resonance (NMR). The TD-DFT scheme was utilized to figure out speculative ultraviolet values and compare them to oscillator strength, electron excitation energies, and spectrum data from experiments. It is evident from the predicted HOMO-LUMO band separation energies that the transmission of charge takes place within a molecule’s structure. The chemical reactivity of the molecule has been calculated along with other global descriptive properties. Scientists investigated how charges move and the density of electrons inside a molecule using NBO analysis of the chemical they were studying. After examining the molecular electrostatic potential (MEP), a 3D picture was created that shows the compound’s nucleophilic and electrophilic areas. In addition to meeting all pertinent pharmacokinetic requirements, 5-amino-3-(2,5-dimethoxyphenyl)-1-isonicotinoyl-2,3-dihydro-1H-pyrazole-4-carbonitrile is also readily absorbed by the gastrointestinal system. Additionally, the chemical that was synthesized had a positive interaction with the target proteins of treatments for viruses, asthma, and heart failure, as shown by molecular docking.

A procedure for the visualization of fingerprint traces on standard and thermal paper using the electron excitation energy of 1,8-diazafluoren-9-one aggregates in a polyvinylpyrrolidone polymer

A procedure for the visualization of fingerprint traces on standard and thermal paper using the electron excitation energy of 1,8-diazafluoren-9-one aggregates in a polyvinylpyrrolidone polymer

Rank-Reduced Equation-of-Motion Coupled Cluster Triples: an Accurate and Affordable Way of Calculating Electronic Excitation Energies.

In the present work, we report an implementation of the rank-reduced equation-of-motion coupled cluster method with approximate triple excitations (RR-EOM-CC3). The proposed variant relies on tensor decomposition techniques in order to alleviate the high cost of computing and manipulating the triply excited amplitudes. In the RR-EOM-CC3 method, both ground-state and excited-state triple-excitation amplitudes are compressed according to the Tucker-3 format. This enables factorization of the working equations such that the formal scaling of the method is reduced to N6, where N is the system size. An additional advantage of our method is the fact that the accuracy can be strictly controlled by proper choice of two parameters defining sizes of triple-excitation subspaces in the Tucker decomposition for the ground and excited states. Optimal strategies of selecting these parameters are discussed. The developed method has been tested in a series of calculations of electronic excitation energies and compared to its canonical EOM-CC3 counterpart. Errors several times smaller than the inherent error of the canonical EOM-CC3 method (in comparison to FCI) are straightforward to achieve. This conclusion holds both for valence states dominated by single excitations and for states with pronounced doubly excited character. Taking advantage of the decreased scaling, we demonstrate substantial computational costs reductions (in comparison with the canonical EOM-CC3) in the case of two large molecules - l-proline and heptazine. This illustrates the usefulness of the RR-EOM-CC3 method for accurate determination of excitation energies of large molecules.

Analytic Gradients for Equation-of-Motion Coupled Cluster with Single, Double, and Perturbative Triple Excitations.

Understanding the process of molecular photoexcitation is crucial in various fields, including drug development, materials science, photovoltaics, and more. The electronic vertical excitation energy is a critical property, for example in determining the singlet-triplet gap of chromophores. However, a full understanding of excited-state processes requires additional explorations of the excited-state potential energy surface and electronic properties, which is greatly aided by the availability of analytic energy gradients. Owing to its robust high accuracy over a wide range of chemical problems, equation-of-motion coupled cluster with single and double excitations (EOM-CCSD) is a powerful method for predicting excited-state properties, and the implementation of analytic gradients of many EOM-CCSD variants (excitation energies, ionization potentials, electron attachment energies, etc.) along with numerous successful applications highlights the flexibility of the method. In specific cases where a higher level of accuracy is needed or in more complex electronic structures, the inclusion of triple excitations becomes essential, for example, in the EOM-CCSD* approach of Saeh and Stanton. In this work, we derive and implement for the first time the analytic gradients of EOMEE-CCSD*, which also provides a template for analytic gradients of related excited-state methods with perturbative triple excitations. The capabilities of analytic EOMEE-CCSD* gradients are illustrated by several representative examples.

Optimization of the thermoelectric performance of aluminum-doped zinc oxide-graphene heterojunctions under high temperature and high pressure

High-pressure effects can be used to effectively optimize the thermoelectric performance of wide-bandgap oxides. We build upon this finding to show that the synergistic effects of doping with aluminum and graphene composite give excellent thermoelectric performance under high pressure. By employing the parabolic band model, the Pisarenko curves are derived at different pressures, coupled with the band structure of Al-doped ZnO. An analysis indicates that pressure-induced narrowing of the bandgap in Al-doped ZnO reduces the electron excitation energy, thereby optimizing the electrical properties of the samples. The Debye Callaway model is also used to fit the lattice thermal conductivity of the samples, thus enabling an in-depth analysis of the phonon scattering mechanisms. Our analysis suggests that graphene composites significantly enhance point defect scattering and Umklapp scattering, thus increasing the phonon relaxation time and effectively reducing the lattice thermal conductivity of the samples. The improvement in the figure of merit (zT) of ZnO is attributed to the simultaneous enhancement of its electrical properties under high pressure and the synergistic optimization of reducing the lattice thermal conductivity through doping and composites. In this work, we consider a fixed doping ratio of Al and a constant proportion of graphene composite, and analyze the microstructure and thermoelectric properties of 0.1C–ZnAl0.04O (C–ZnAlO) samples synthesized under pressures ranging from 1 to 5 GPa, with the aim of elucidating the influence of pressure and graphene composite on the electro-acoustic transport properties of ZnO. We find that the zT value for a sample synthesized at 5 GPa is increased to 0.27 at 973 K.

The Pigment World: Life's Origins as Photon-Dissipating Pigments.

Many of the fundamental molecules of life share extraordinary pigment-like optical properties in the long-wavelength UV-C spectral region. These include strong photon absorption and rapid (sub-pico-second) dissipation of the induced electronic excitation energy into heat through peaked conical intersections. These properties have been attributed to a "natural selection" of molecules resistant to the dangerous UV-C light incident on Earth's surface during the Archean. In contrast, the "thermodynamic dissipation theory for the origin of life" argues that, far from being detrimental, UV-C light was, in fact, the thermodynamic potential driving the dissipative structuring of life at its origin. The optical properties were thus the thermodynamic "design goals" of microscopic dissipative structuring of organic UV-C pigments, today known as the "fundamental molecules of life", from common precursors under this light. This "UV-C Pigment World" evolved towards greater solar photon dissipation through more complex dissipative structuring pathways, eventually producing visible pigments to dissipate less energetic, but higher intensity, visible photons up to wavelengths of the "red edge". The propagation and dispersal of organic pigments, catalyzed by animals, and their coupling with abiotic dissipative processes, such as the water cycle, culminated in the apex photon dissipative structure, today's biosphere.

Theory for proton-coupled energy transfer.

In the recently discovered proton-coupled energy transfer (PCEnT) mechanism, the transfer of electronic excitation energy between donor and acceptor chromophores is coupled to a proton transfer reaction. Herein, we develop a general theory for PCEnT and derive an analytical expression for the nonadiabatic PCEnT rate constant. This theory treats the transferring hydrogen nucleus quantum mechanically and describes the PCEnT process in terms of nonadiabatic transitions between reactant and product electron-proton vibronic states. The rate constant is expressed as a summation over these vibronic states, and the contribution of each pair of vibronic states depends on the square of the vibronic coupling as well as the spectral convolution integral, which can be viewed as a generalization of the Förster-type spectral overlap integral for vibronic rather than electronic states. The convolution integral also accounts for the common vibrational modes shared by the donor and acceptor chromophores for intramolecular PCEnT. We apply this theory to model systems to investigate the key features of PCEnT processes. The excited vibronic states can contribute significantly to the total PCEnT rate constant, and the common modes can either slow down or speed up the process. Because the pairs of vibronic states that contribute the most to the PCEnT rate constant may correspond to spectroscopically dark states, PCEnT could occur even when there is no apparent overlap between the donor emission and acceptor absorption spectra. This theory will assist in the interpretation of experimental data and will guide the design of additional PCEnT systems.

Transfer of Electronic Excitation Energy Between Thioflavin T and Its Styryl Derivatives Incorporated Into Amyloid Fibrils

Transfer of Electronic Excitation Energy Between Thioflavin T and Its Styryl Derivatives Incorporated Into Amyloid Fibrils

Single-Electron Qubits Based on Quantum Ring States on Solid Neon Surface.

Single electrons trapped on solid-neon surfaces have recently emerged as a promising platform for charge qubits. Experimental results have revealed their exceptionally long coherence times, yet the actual quantum states of these trapped electrons, presumably on imperfectly flat neon surfaces, remain elusive. In this Letter, we examine the electron's interactions with neon surface topography, such as bumps and valleys. By evaluating the surface charges induced by the electron, we demonstrate its strong perpendicular binding to the neon surface. The Schrödinger equation for the electron's lateral motion on the curved 2D surface is then solved for extensive topographical variations. Our results reveal that surface bumps can naturally bind an electron, forming unique quantum ring states that align with experimental observations. We also show that the electron's excitation energy can be tuned using a modest magnetic field to facilitate qubit operation. This study offers a leap in our understanding of electron-on-solid-neon qubit properties and provides strategic insights on minimizing charge noise and scaling the system to propel forward quantum computing architectures.

Linear and nonlinear optical properties of hybrid Polyaniline/CoFe2O4 nanocomposites: Electrochemical synthesis, characterization, and analysis

This study presents a focused investigation and comprehensive analysis of the synthesis of hybrid Polyaniline/Cobalt ferrite (PANI/CoFe2O4) nanocomposites using an optimized electrochemical polymerization method. CoFe2O4 nanoparticles (NPs) were incorporated into the PANI matrix at varying concentrations (3, 6, and 12 wt%). The research examined the newly synthesized hybrid nanocomposites in terms of their structure, dielectric properties, and both linear and nonlinear optical properties. As a result of the Williamson-Hall method, the average crystallite size varied between 45 and 99 nm. Initially, adding a small quantity of NPs decreased the nanocomposite size, but further additions increased it due to aggregation. The Tauc plot showed a gradual increase in the energy band gap of the films as the concentration of CoFe2O4 NPs increased up to 12 wt%. This trend showed stronger absorption bands and higher coefficients, indicating improved light absorption compared to pure PANI films. Dielectric properties, including dielectric constants (ɛr, ɛi) and dielectric loss (tan δ), were examined as a function of frequency. The experimental results indicated that PANI/CoFe2O4 exhibited lower dielectric constants than bare PANI. Concentration-dependent optical properties, such as electronic transition excitation energies, dispersion energies, and optical conductivity, were also investigated. These properties were modeled using a single oscillator based on the Wemple-DiDomenico (WDD) approach. The study revealed a reduction in key optical parameters—linear susceptibility, nonlinear third-order susceptibility, and nonlinear refractive index—as nanoparticle content increased. Conversely, increasing concentrations of CoFe2O4 NPs led to a significant increase in the ratio of free carriers to effective mass (N/m٭), from 3.89 × 10³⁶ to 4.04 × 10³⁶ m⁻³ kg⁻1. Additionally, the electrical conductivity of both PANI and PANI/CoFe2O4 nanocomposites exhibited temperature-dependent improvement, reaching maximum values. The observed findings indicate that hybrid PANI-CoFe2O4 nanocomposites possess enhanced properties, highlighting their promising potential as active materials for a broad range of optoelectronic applications.

Performance of range-separated long-range SOPPA short-range density functional theory method for vertical excitation energies.

In this paper, benchmark results are presented on the calculation of vertical electronic excitation energies using a long-range second-order polarization propagator approximation (SOPPA) description with a short-range density functional theory description based on the Perdew-Burke-Ernzerhof (PBE) functional. The excitation energies are investigated for 132 singlet states and 71 triplet states across 28 medium-sized organic molecules. The results show that overall SOPPA-srPBE always performs better than PBE and that SOPPA-srPBE performs better than SOPPA for singlet states, but slightly worse than SOPPA for triplet states when CC3 results are the reference values.

Efficient removal of bisphenol A from water using a novel organic–inorganic hybrid heterojunction

Organic-inorganic hybrid heterojunctions have the ability to efficiently remove trace pollutants from water due to efficient photosensitivity. In this work, an organic–inorganic hybrid S-scheme heterojunction photosensitizer (RCP-BW) was successfully fabricated by growing cross-linked β-CD/riboflavin copolymer on the surface of bismuth tungstate (Bi2WO6). The fabrication of the copolymer retains the photosensitivity of riboflavin and the confinement effect of β-CD and forms an internal electric field with Bi2WO6 to enhance the photoelectron transport ability. Photogenerated electrons are transferred and stacked from Bi2WO6 to β-CD/riboflavin copolymers, which greatly enhances the ability of organic copolymers to reduce oxygen and produce superoxide radicals. We combined electrochemistry, free radical chemistry and DFT to study the photoelectron migration mechanism and photocatalytic performance enhancement mechanism in S-scheme heterojunctions. The pseudo-first-order reaction kinetic constant (kRCP-BW = 0.081 min−1) for BPA degradation was four times that of unmodified BW (kBW = 0.020 min−1). β-CD regulates the band structure of riboflavin to match with Bi2WO6, and utilizes charged contaminants and intermediate degradation products to promote the production of reactive oxygen species through interface electron transfer and excited state transition energy transfer. This work provides theoretical support and technical means for photocatalytic oxidation technology to control endocrine disruptors.