Analysis Of Potential Energy Curves Research Articles

Influence of atomic electronegativity on ESIPT behaviour for the BTDI and its derivatives: Theoretical exploration

In this work, we theoretically explored the influence of atomic electronegativity on excited-state intramolecular proton transfer (ESIPT) behavior among novel fluorescent probes BTDI and its derivatives (BODI and BSeDI). A thorough examination of the optimized structural parameters and infrared vibrational spectra reveals an enhancement in intramolecular hydrogen bonding within BTDI and its derivatives upon light excitation. This finding is further reinforced by topological analysis and interaction region indicator scatter plots, which underscores the sensitivity of atomic electronegativity to variations in hydrogen bonding strength. With regards to absorption and fluorescence spectra, the decrease in atomic electronegativity leads to a pronounced redshift, primarily attributed to the narrowing of the energy gap. Additionally, an analysis of potential energy curves and the exploration of intrinsic reaction coordinate paths based on transition state structures afford a deeper understanding of the mechanism underlying ESIPT and being modulated through the manipulation of atomic electronegativity. We anticipate that this work on atomic electronegativity regulating ESIPT behavior will serve as a catalyst for novel fluorescent probes in the future, offering fresh perspectives and insights.

Extensive Study of Modern Approaches Used in Identifying the Buckingham Potential

This paper presents two mathematical approaches of estimating unknown parameters of the Buckingham potential. Two functional forms of the potential was investigated owing to the complexities and difficulties arising from the original Buckingham potential. These complexities are due to the combination of both powers and an exponent in mathematical representation of the potential. Hence, we decided to consider approximating the parameters of the simpler form, widely known as the modified Buckingham potential. The method of least squares (differential and integral methods) were used to estimate the potential parameters and the calculation of the optimized values of the constructed goal function were included in the paper. The calculated estimates showed reasonable agreement with experimental datasets of copper atoms over a large vicinity of the interatomic potential distance. This conclusion was reached through the graphical analysis of potential energy curves and through the error between the respective curves. Optimized goal function values were used to compare the efficiency of the methods.

A theoretical study of solvent effect on the excited state intramolecular proton transfer of 3‐hydroxyflavone

AbstractIn order to study the effect of solvents polarity on the excited state intramolecular proton transfer (ESIPT) processes of 3‐hydroxyflavone (3HF) in detail, the ESIPT processes of 3HF in toluene, dichloromethane (DCM), and acetonitrile (ACN) were investigated using theoretical methods. The stable configurations of 3HF in ground (S0) and excited (S1) states were optimized. The critical configuration parameters, infrared (IR) vibrational spectra, absorption and fluorescence spectra, frontier molecular orbitals (MOs), charge distribution, and potential energy curves were calculated. The intramolecular hydrogen bonds are obviously enhanced and the electronic density redistributes when excited to S1 state. The strengthening of intramolecular hydrogen bonds and the redistribution of electronic density are beneficial to the ESIPT processes. The analysis of potential energy curves show that the proton transfer processes are feasible in thermodynamics in S1 state, but not in S0 state. In addition, the intramolecular hydrogen bonds gradually weaken when the solvents polarity increases from toluene, DCM to ACN. As the solvents polarity increases, the ESIPT processes are more and more difficult to occur. It can be concluded that the strength of intramolecular hydrogen bonds will be affected by the solvents polarity, and the strength of intramolecular hydrogen bonds are directly related to the difficulty of the ESIPT processes.

Absorption band structure of the photochromic dimethyldihydropyrene/metacyclophanediene couple. Insight from vibronic coupling theory.

A detailed insight behind the structure of absorption bands of the photochromic couple dimethyldihydropyrene (DHP)/metacyclophanediene (CPD) is studied employing vibronic coupling theory. Two separate model molecular Hamiltonians, including a maximum of four electronic states and 18 vibrational modes for DHP and five electronic states and 20 vibrational modes for CPD, are constructed in a diabatic electronic representation. The parameters of the Hamiltonians are estimated from the electronic energies obtained from extensive density functional theory (DFT) and time-dependent DFT calculations. Based on these Hamiltonians' parameters, a detailed analysis of potential energy curves is performed in conjunction with positional and energetic locations of several stationary points in multi-dimensional potential energy surfaces. Based on the results of electronic structure calculations, quantum nuclear dynamics studies on the electronic excited states of DHP and CPD are performed to understand the impact of non-adiabatic effects on the formation of vibronic structures of absorption bands of these photo-isomers.

Internal acylation-induced AIE/AIEE switch of pyrimido[2,1-b][1,3]benzothiazoles (PBTs): Restriction of access to dark state caused by distortion of 4H-pyrimidine ring

As atypical propeller-shaped AIEgens, pyrimido[2,1-b][1,3]benzothiazoles (PBTs) exhibit good to excellent solid-state fluorescence quantum yields and full-color tunability. However, the working mechanism of PBT AIEgens still remains elusive. In this article, three internally acylated PBTs (PBT-B7−B9) were synthesized. In agreement with our previous report, locking the exocyclic ester resulted in the emergence of solution-phase fluorescence, i.e. AIE/AIEE switch. Theoretical calculation results indicated that the 4H-pyrimidine ring experiences the most significant electronic structure alterations upon excitation. Comparative analysis of potential energy curves (PECs) and optimized excited-state geometries of both locked and unlocked PBTs revealed that as a cumulative result of bond length/angle changes in 4H-pyrimidine, the distortion of the ring is the direct cause for decoupling of π-conjugated MOs and major driving force for access to the resulting dark state. On the other hand, the restriction of rotation of exocyclic ester or carbonyl in locked PBTs maintains the conformation of 4H-pyrimidine, thereby avoiding the generation of dark state and making them emissive in solution. This AIE mechanism well explained the drastically decreased fluorescence quantum yields of unlocked PBTs in PMMA films, and indicated that locking the exocyclic ester or carbonyl could be an effective strategy to improve their PL performance in polymer matrix.

Effects of solvents on the excited‐state intramolecular proton transfer in 3‐HTC

AbstractIt has been demonstrated experimentally that proton transfer can occur in the excited state of 3‐hydroxy‐2‐mercapto‐4‐one (3‐HTC) molecule. However, the effect of solvent polarity on excited‐state intramolecular proton transfer of 3‐HTC has not been reported. In this paper, the molecular structures of ground and excited states in different solvents are optimized by density functional theory and time‐dependent density functional theory. Based on the optimized structure, infrared vibration frequency, electronic spectra, natural bond orbital (NBO) population, and potential energy curves were calculated and analyzed. By analyzing the bond lengths and the bond angles related to the hydrogen bond, it can be seen that the intramolecular hydrogen bond intensity of 3‐HTC molecule in the S1state is strengthened in different solvents. With the increase of the solvent polarity, the degree of hydrogen bond strength decreases. Through the analysis of the infrared vibration frequency, it could be found that intramolecular hydrogen bond of 3‐HTC is weakened as the solvent polarity increases. By analyzing the frontier molecular orbitals and the charge density difference (CDD) maps, it is proved that charge transfer occurs during photoexcitation, which promotes the excited‐state proton transfer process. Further, the analysis of potential energy curves of 3‐HTC in the ground state and S1state shows that proton transfer can be realized in the S1state of 3‐HTC in different solvents. With the increase of solvent polarity, the difficulty of intramolecular proton transfer is increasing.

Variational Localized Active Space Self-Consistent Field Method.

Fragmentation methods applied to multireference wave functions constitute a road toward the application of highly accurate ab initio wave function calculations to large molecules and solids. However, it is important for reproducibility and transferability that a fragmentation scheme be well defined with minimal dependence on initial orbital guesses or user-designed ad hoc fragmentation schemes. One way to improve this sort of robustness is to ensure that the energy obeys a variational principle; that is, the active orbitals and active space wave functions minimize the electronic energy in a certain ansatz for the molecular wave function. We extended the theory of the localized active space self-consistent field, LASSCF, method (JCTC 2019, 15, 972) to fully minimize the energy with respect to all orbital rotations, rendering it truly variational. The new method, called vLASSCF, substantially improves the robustness and reproducibility of the LAS wave function compared to LASSCF. We analyze the storage and operation cost scaling of vLASSCF compared to orbital optimization using a standard complete active space self-consistent field (CASSCF) approach, and we show results of vLASSCF calculations on some simple test systems. We show that vLASSCF is energetically equivalent to CASSCF in the limit of one active subspace and that vLASSCF significantly improves upon the reliability of LASSCF energy differences, allowing for more meaningful and subtle analysis of potential energy curves of dissociating molecules. We also show that all forms of LASSCF have a lower operation cost scaling than the orbital optimization part of CASSCF.

DFT-TDDFT investigation of excited-state intramolecular proton transfer in 2-(2′-hydroxyphenyl)benzimidazole derivatives: Effects of electron acceptor and donor groups

The excited-state intramolecular proton transfer (ESIPT) reactions of 2-(2′-hydroxyphenyl)benzimidazole (HBI) derivatives were investigated using time-dependent density functional theory (TD-DFT) method at B3LYP/TZVP theoretical level. The geometric parameters, infrared (IR) vibrational spectra, frontier molecular orbitals (MOs), Mulliken charge distribution analysis, natural bond orbital (NBO) analysis and potential energy curves were calculated to provide the direct information about the effect of electron acceptor and donor groups on the ESIPT reactions. The intramolecular hydrogen bonds are significantly strengthened and the electronic density is redistributed after a vertical excitation to S1 state. The proton transfer (PT) reactions are unlikely occur in S0 state through the analysis of potential energy curves and the Hartree-Fock energy of the stable structures. The presence of the electron acceptor NO2 group can facilitate the ESIPT reaction, while the presence of electron donor NH2 group can hinder the ESIPT reaction. In general, the electron acceptor NO2 group and electron donor NH2 group can influence the ESIPT reactions in a completely different way.

Photoinduced excited state intramolecular proton transfer and spectral behaviors of Aloesaponarin 1

The novel spectral behaviors of Aloesaponarin 1 (AS1) are investigated by studying the dynamics process of excited state intramolecular proton transfer (ESIPT). Two intramolecular hydrogen bonds (HB1 and HB2) are formed between hydroxyl and carbonyl groups of AS1. The calculated potential energy curves of AS1 demonstrate that the ESIPT process along HB1 is energy favorable while not along HB2. The analysis of potential energy curves describes clearly the dynamic behaviors of the proton transfer process from hydroxyl group to carbonyl group along HB1. The infrared spectra of AS1 confirm that the stretching absorption peak of hydroxyl group in HB1 disappears and that a new peak corresponding to hydroxyl group appears in the first excited state, which depicts the ESIPT process indirectly. The fluorescence peaks of AS1 (636nm), AS2 (Aloesaponarin 1 3-O-methyl ether, 629nm) and AS3 (Aloesaponarin 1 8-O-methyl ether, 522nm) demonstrate that the fluorescence behavior of AS1 is primarily effected by HB1 rather than HB2. The large Stokes shifts of AS1 (206nm) indicate that the absorbed energy is partly transferred to non-harmful long fluorescence through ESIPT process, which plays important role in the explanation for the UV protection property of AS1. The inducement and influence factors of ESIPT process of AS1 are illustrated by analyzing electrostatic potential, molecular orbital and natural bond orbital.

The Hyperbolic Chemical Bond: Fourier Analysis of Ground and First Excited State Potential Energy Curves of HX (X = H−Ne)

RHF/aug-cc-pVnZ, UHF/aug-cc-pVnZ, and QCISD/aug-cc-pVnZ, n = 2-5, potential energy curves of H2 X (1) summation g (+) are analyzed by Fourier transform methods after transformation to a new coordinate system via an inverse hyperbolic cosine coordinate mapping. The Fourier frequency domain spectra are interpreted in terms of underlying mathematical behavior giving rise to distinctive features. There is a clear difference between the underlying mathematical nature of the potential energy curves calculated at the HF and full-CI levels. The method is particularly suited to the analysis of potential energy curves obtained at the highest levels of theory because the Fourier spectra are observed to be of a compact nature, with the envelope of the Fourier frequency coefficients decaying in magnitude in an exponential manner. The finite number of Fourier coefficients required to describe the CI curves allows for an optimum sampling strategy to be developed, corresponding to that required for exponential and geometric convergence. The underlying random numerical noise due to the finite convergence criterion is also a clearly identifiable feature in the Fourier spectrum. The methodology is applied to the analysis of MRCI potential energy curves for the ground and first excited states of HX (X = H-Ne). All potential energy curves exhibit structure in the Fourier spectrum consistent with the existence of resonances. The compact nature of the Fourier spectra following the inverse hyperbolic cosine coordinate mapping is highly suggestive that there is some advantage in viewing the chemical bond as having an underlying hyperbolic nature.

A calculation of the spectroscopic constants for several states of NF

Spectroscopic constants for NF are determined from a Dunham analysis of potential energy curves computed previously by means of a valence configuration interaction method. Results are presented for several experimentally known and unknown states within the 3 Sigma -, 1 Delta , 1 Sigma +, 1 Sigma -, 3 Delta and 3 Sigma + symmetry species. Where possible, our findings are compared with other calculations and with experiment.

Ab initio calculations on intermolecular forces. II. An analysis of potential energy curves for HE… HF, He… H 2O, H 2… HF and H 2 … H 2O at large and intermediate distances

Previous calculations for He… HF and He… H 2O are extended to the systems H 2… HF and H 2 … H 2O. The interaction energy is calculated both in the SCF approximation and with the inclusion of the intersystem correlation energy. The results show that in order to obtain quantitative information about the interaction energy (for the systems discussed here) configuration interaction calculations have to be performed. In fact, near the energy minimum the contributions accounted for in the SCF approximation are of equal importance as those which result from the intersystem correlation. The interaction energies in all four pairs are compared with those of model calculations in which the polar components HF and H 2O are represented by their dipole and quadrupole momentS. Illustrative is further the decomposition of the stabilization energy Δ E SCF into Coulomb, exchange and (polarization + charge transfer) contributions. The difficulties for the interpretation, which are due to the fact that the distance R between two charge distributions is not uniquely defined, are discussed,

Étude de l'énergie cinétique des produits de la dissociation collisionnelle d'ions CH n+ d'énergie 40 keV : II. Dissociation de CH +

The kinetic energy of protons and hydrogen atoms arising from collisional dissociation of 40 keV CH + ions has been measured by electrostatic analysis, after reionization of the neutrals. The distribution of the kinetic energy released by the dissociation CH + → C + + H, which has maxima at 0.3 and 2.9 eV, is similar to that determined by another method and consistent with suppositions based upon the analysis of potential energy curves of CH + and of the lifetime of some transitions. The distribution of the kinetic energy released by the dissociations CH + → C + H + and CH + → C + + H + + e, which has never been studied, exhibits maxima at 0.7, 1.2, 2.9, 5.7 and 8.4 eV, which are also consistent with the suppositions.