呋喃查尔酮结构与电子光谱的密度泛函理论研究

在密度泛函理论的PBE1PBE/6-31G(d)水平上对呋喃查尔酮及其衍生物的几何结构进行优化计算.在获得基态稳定结构的基础上,应用含时密度泛函理论计算其电子吸收光谱,探讨了取代基和溶剂对电子吸收光谱的影响,计算结果与实验结果吻合很好,平均绝对偏差仅为3.3nm(0.04eV).结果表明,取代基的引入和溶剂极性的增大均使光谱发生红移.通过前线轨道分析,揭示了该类化合物的主要吸收峰均源自分子中HOMO→LUMO电子跃迁.     

DFT study of the gas‐phase thermal decomposition kinetics of 2‐ethoxypyridine into 2‐pyridone

The mechanism of the gas‐phase elimination kinetics of 2‐ethoxypyridine has been studied through the electronic structure calculations using density functional methods: B3LYP/6‐31G(d,p), B3LYP/6‐31++G(d,p), B3PW91/6‐31G(d,p), B3PW91/6‐31++G(d,p), MPW1PW91/6‐31G(d,p), MPW1PW91/6‐31++G(d,p), PBEPBE/6‐31G(d,p), PBEPBE/6‐31++G(d,p), PBE1PBE1/6‐31G(d,p), and PBE1PBE1/6‐31++G(d,p). The elimination reaction of 2‐ethoxypyridine occurs through a six‐centered transition state geometry involving the pyridine nitrogen, the substituted carbon of the aromatic ring, the ethoxy oxygen, two carbons of the ethoxy group, and a hydrogen atom, which migrates from the ethoxy group to the nitrogen to give 2‐pyridone and ethylene. The reaction mechanism appears to occur with the participation of π‐electrons, similar to alkyl vinyl ether elimination reaction, with simultaneous ethylene formation and hydrogen migration to the pyridine nitrogen producing 2‐pyridone. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

QM/MM calculation of solvent effects on absorption spectra of guanine

Electronic spectra of guanine in the gas phase and in water were studied by quantum mechanical/molecular mechanical (QM/MM) methods. Geometries for the excited‐state calculations were extracted from ground‐state molecular dynamics (MD) simulations using the self‐consistent‐charge density functional tight binding (SCC‐DFTB) method for the QM region and the TIP3P force field for the water environment. Theoretical absorption spectra were generated from excitation energies and oscillator strengths calculated for 50 to 500 MD snapshots of guanine in the gas phase (QM) and in solution (QM/MM). The excited‐state calculations used time‐dependent density functional theory (TDDFT) and the DFT‐based multireference configuration interaction (DFT/MRCI) method of Grimme and Waletzke, in combination with two basis sets. Our investigation covered keto‐N7H and keto‐N9H guanine, with particular focus on solvent effects in the low‐energy spectrum of the keto‐N9H tautomer. When compared with the vertical excitation energies of gas‐phase guanine at the optimized DFT (B3LYP/TZVP) geometry, the maxima in the computed solution spectra are shifted by several tenths of an eV. Three effects contribute: the use of SCC‐DFTB‐based rather than B3LYP‐based geometries in the MD snapshots (red shift of ca. 0.1 eV), explicit inclusion of nuclear motion through the MD snapshots (red shift of ca. 0.1 eV), and intrinsic solvent effects (differences in the absorption maxima in the computed gas‐phase and solution spectra, typically ca. 0.1–0.3 eV). A detailed analysis of the results indicates that the intrinsic solvent effects arise both from solvent‐induced structural changes and from electrostatic solute–solvent interactions, the latter being dominant. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Spectral shifts of the n → π* and π → π* transitions of uracil based on a modified form of solvent reorganization energy

According to our recent studies on the nonequilibrium solvation, the solvent reorganization energy is found to be the cost of maintaining the residual polarization P', which equilibrates with the extra electric field E(ex). On the basis of this solvent reorganization energy and the well-established equilibrium solvation energy, a novel and reasonable expression for the spectral shift of the electronic absorption spectra is proposed in this work. Furthermore, the two lowest transitions of uracil in aqueous solution are investigated as test cases with the TDDFT/6-311++G** method. The obtained spectral shift is 0.48 eV for n → π* transition and -0.14 eV for π → π* transition, agreeing well with available experimental results. The contributions to the shift are discussed and the electrostatic plus polarization components are found to be crucial for the electronic absorption spectra of uracil in aqueous solution.     

态定(线性响应)-极化连续模型/含时密度泛函方法研究一种有机发光材料的吸收和发射光谱

3-(二氰亚甲基)-5,5-二甲基-1-(3-[9-(2-乙基-己基)-咔唑基]-乙烯基)环己烷(DCDHCC)是一种用于光电器件中的有机染料,它具有良好的发光特性.我们使用含时密度泛函方法(TD-PBE0,TD-BMK和TD-M06)以及极化连续模型(PCM)计算了该材料在溶剂中的吸收和发射特性.计算中使用了线性响应(LR)、态定(SS)两种溶剂模型和6-31G(d)、6-31+G(d,p)两种基组.计算了DCDHCC在苯、四氢呋喃和丙酮溶剂中的吸收和发射光谱,并与实验观测进行了比较.结果表明:对于吸收光谱的计算,杂化函数的影响大于基组和溶剂模型,在三种函数中BMK更适于研究DCDHCC的吸收光谱;而对于发射光谱,基组的影响最大,基组通过影响激发态构型从而影响发射光谱,对于激发态构型的优化需要使用6-31+G(d,p)基组.我们希望这些研究能对今后设计类似的发光分子有帮助.     

A Time‐Dependent DFT Study of the Absorption and Fluorescence Properties of Graphene Quantum Dots

Absorption and fluorescence spectra of graphene quantum dots (GQDs) have been computed by using time‐dependent density functional theory (TDDFT). Different functionals, including PBE, TPSSh, B3LYP, PBE0, CAM‐B3LYP, and LC‐ωPBE, have been tested and B3LYP/6‐31G(d) has been proven to be the most accurate method for our work. The bulk solvent effects of toluene and dichloromethane have been assessed by using the polarizable continuum model (PCM). The absorption wavelength of GQDs in solvents is red‐shifted compared with that in the gas phase. Edge functionalization effects analysis shows that a small number of substituted groups on GQDs induce a small redshift whereas a large redshift occurs when the edges of GQDs are all decorated. Little difference in the fluorescent emission was observed in solvents and in the gas phase. Molecular orbital transition and transition density matrix analysis have been performed. The electronic transition mainly occurs in the middle part of the structure of C132. The strong absorption of C132 corresponds to a S₀→S₃ transition and the fluorescence emission is ascribed to a S₁→S₀ transition, which indicates that Kasha’s rule is obeyed.     

Polarizable continuum model with the fragment molecular orbital-based time-dependent density functional theory

The polarizable continuum model (PCM) for describing the solvent effect was combined with the fragment molecular orbital-based time-dependent density functional theory (TDDFT). Several levels of the many-body expansion were implemented, and the importance of the many-body contributions to the singlet-excited states was discussed. To calibrate the accuracy, we performed a number of the model calculations using our method and the regular TDDFT in solution, applying them to phenol and polypeptides at the long-range corrected BLYP/6-31G* level. It was found that for systems up to 192 atoms the largest error in the excitation energy was 0.006 eV (vs. the regular TDDFT/PCM of the full system). The solvent shifts and the conformer effects were discussed, and the scaling was found to be nearly linear. Finally, we applied our method to the lowest singlet excitation of the photoactive yellow protein (PYP) in aqueous solution and determined the excitation energy to be in reasonable agreement with experiment. The excitation energy analysis provided the contributions of individual residues, and the main factors as well as their solvent shifts were determined.     

TDDFT Study of the Electronic Structure,Absorption and Emission Spectra of the Light Emitters of the Amazing Firefly Bioluminescence and Solvation Effects on the Spectra

The ground and excited state properties of luciferin (LH₂) and oxyluciferin (OxyLH₂), the bioluminescent chemicals in the firefly, have been characterized using density functional theory (DFT) and time dependent DFT (TDDFT) methods. The effects of solvation on the electronic absorption and emission spectra of luciferin and oxyluciferin were predicted with a self‐consistent isodensity polarized continuum model of the solvent using TDDFT. The S₀→S₁ vertical excitation energies in the gas phase and in water were obtained. Optimizations of the excited state geometries permitted the first predictions of the fluorescence spectra for these biologically important molecules. Shifts in both of the absorption and emission spectra on proceeding from the gas phase to aqueous solution were also predicted.     

Tunable solvatochromic response of newly synthesized antioxidative naphthalimide derivatives: intramolecular charge transfer associated with hydrogen bonding effect

The solvatochromic behavior of two newly synthesized naphthalimide derivatives (I and II) which have potential antioxidative activities in anticarcinogenic drug development treatment, has been monitored in protic and aprotic solvents of different polarity applying steady-state and time-resolved fluorescence techniques. The compounds exhibit unique photophysical response in different solvent environments. The spectral trends do not appear to originate only from changes in the solvent polarity but also indicate that hydrogen bonding interactions and intramolecular charge transfer (ICT) influence the energy of electronic excitation of the compounds. Incorporation of an amino group at C(4) position of the naphthalimide ring in II makes it behave differently from I in terms of spectral characterization and fluorescence efficacy of the systems. The nonradiative relaxation process of the compounds is governed by medium polarity. The ground state geometry, lowest energy transition, and the UV-vis absorption energy of the compounds were studied using density functional theory (DFT) and time-dependent density functional theory (TDDFT) at the B3LYP/6-31G* level, which showed that the calculated outcomes were in good agreement with experimental data.     

Quantum Chemical Study Aimed at Modeling Efficient Aza-BODIPY NIR Dyes: Molecular and Electronic Structure,Absorption, and Emission Spectra

A comprehensive study of the molecular structure of aza-BODIPY and its derivatives, obtained by introduction of one or more substituents, was carried out. We considered the changes in the characteristics of the electronic and geometric structure of the unsubstituted aza-BODIPY introducing the following substituents into the dipyrrin core; phenyl, 2-thiophenyl, 2-furanyl, 3-pyridinyl, 4-pyridinyl, 2-pyridinyl, and ethyl groups. The ground-state geometries of the unsubstituted Aza-BODIPY and 27 derivatives were computed at the PBE/6-31G(d) and CAM-B3LYP/6-31+G(d,p) levels of theory. The time-dependent density-functional theory (TDDFT) together with FC vibronic couplings was used to investigate their absorption and emission spectra.     

Density functional theory studies on the electronic and vibrational spectra of octaethylporphyrin diacid

The ground-state structure and electronic and vibrational spectra of octaethylporphyrin diacid (H4OEP2+) have been studied with the density functional theory. The geometrical parameters computed with B3LYP, PBE1PBE and mPW1PW91 functionals and 6-31G* basis sets are well consistent with the experimental values. Electronic absorption spectrum of H4OEP2+ has been studied with the time-dependent DFT method, and the calculated excitation energies and oscillator strengths are compared with the experimental results. The Raman and IR spectra of H4OEP2+ and the Raman spectrum of its N-deuterated analogue (D4OEP2+) were measured. The observed Raman and IR bands have been assigned based on the frequency calculations at the B3LYP/6-31G* level of theory.     

Theoretical studies of molecular structures and properties of platinum (II) antitumor drugs

The molecular structure and vibration spectra of carboplatin were investigated by the different density functional models (mPW1PW, BPV86, HCTH, PBEPBE, LSDA and PBE1PBE) using several basis sets including LANL2DZ, SDD, LANL2MB, CEP-4G, CEP-31G and CEP-121G. The results indicate that LSDA/SDD and LSDA/LANL2DZ levels are clearly superior to all the remaining density functional methods in predicting the structures of carboplatin. Mean absolute deviation between the calculated harmonic and observed fundamental vibration frequencies for each method indicates that PBE1PBE/CEP-121G and PBE1PBE/SDD methods are sufficient to predict vibration spectrum of carboplatin comparing with other DFT methods.     

Theoretical investigation of azo dyes adsorbed on cellulose fibers: 2. Spectroscopic study

Electronic absorption spectra and the frontier orbitals of 1-arylazo-2-naphtol dyes are computed and analyzed in four models, namely in the gas phase (model I), in a solvent (model I + CPCM), adsorbed on the cellulose surface (model II), and model II in the presence of solvent (model II + CPCM) via time-dependent density functional theory (TD-DFT) and conductor-like polarizable continuum model (CPCM) at the B3LYP/6-31G** level of theory. A bathochromic shift is observed for the λ_max peak due to both short-range and long-range interactions of the non-ionic dyes with cellulose, while the ionic dyes exhibit hypsochromic shift in their λ_max peak. The results predict that the studied dyes should be nearly yellow after being adsorbed on cellulose with excellent color strength. Furthermore, the ionic dyes are suitable for the dyeing of cellulose fibers. The nuclear magnetic resonance (NMR) chemical shieldings calculated for the azo dyes in the gas phase and adsorbed states and for their tautomeric equilibrium mixtures show that the NMR technique can be used successfully to follow the dyeing process.     

Synthesis,Characterization and Theoretical Studies on a Thiocarbamide Derivative Containing Schiff Base Group

A thiocarbamide derivative containing Schiff base groups,1,5-bis[4-(dimethylamino)benzylidene]thiocarbonohydrazide,has been synthesized and characterized by elemental analysis,IR,1H NMR,UV and X-ray single-crystal diffraction.Density function theory(DFT) calculations at the B3LYP/6-31G* and PBE0/6-31G* levels for optimized geometries and electronic transition spectra have been performed.Comparative studies show that both B3LYP/6-31G* and PBE0/6-31G* methods can well reproduce the molecular structure,and the latter is more reliable than the former to simulate electronic spectra.NPA calculational results at the B3LYP/6-31G* level indicate the title compound to be a potential multidentate ligand to the metallic ions.Based on the vibrational analysis,thermodynamic properties at different temperatures have been obtained.     

Packing Structures of Thiophene Dimers and Their Effects on Excitation Energies of Thiophene Dimers

IntroductionPi(π) conjugated polymers have received exten-sive experimental and theoretical attention because oftheir fascinating electronic and optical properties[1—3].Recently, many new experiment results[4—6]have re-vealed that the inter-chain inter…     

Theoretical investigation of solvent effects on tautomeric equilibrium of 2‐diazo‐4,6‐dinitrophenol

The density functional theory has been used to study the tautomeric equilibrium of 2‐diazo‐4,6‐dinitrophenol(DDNP) in the gas phase and in 14 solvents at the B3LYP/6‐31G* level. The solvent effects on the tautomeric equilibria were investigated by the self‐consistent reaction field theory (SCRF) based on conductor polarized continuum model (CPCM) in apolar and polar solvents and by the hybrid continuum‐discrete model in protic solvent, respectively. Solvent effects on the computed molecular properties, such as molecular geometries, dipole moments, E_LUMO, E_HOMO, total energies for DDNP tautomers and transition state, tautomerization energies and solvation energies have been found to be evident. The tautomeric equilibrium of DDNP is solvent‐dependent to a certain extent. The tautomer I (cyclic azoxy form) is preferred in the gas phase, while in nonpolar solvents tautomer I and II (quinold form) exist in comparable amounts, and in highly polar solvents, the tautomeric equilibrium is shifted in favor of the more polar tautomer II . © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Highly efficient implementation of pseudospectral time‐dependent density‐functional theory for the calculation of excitation energies of large molecules

We have developed and implemented pseudospectral time‐dependent density‐functional theory (TDDFT) in the quantum mechanics package Jaguar to calculate restricted singlet and restricted triplet, as well as unrestricted excitation energies with either full linear response (FLR) or the Tamm–Dancoff approximation (TDA) with the pseudospectral length scales, pseudospectral atomic corrections, and pseudospectral multigrid strategy included in the implementations to improve the chemical accuracy and to speed the pseudospectral calculations. The calculations based on pseudospectral time‐dependent density‐functional theory with full linear response (PS‐FLR‐TDDFT) and within the Tamm–Dancoff approximation (PS‐TDA‐TDDFT) for G2 set molecules using B3LYP/6‐31G*^* show mean and maximum absolute deviations of 0.0015 eV and 0.0081 eV, 0.0007 eV and 0.0064 eV, 0.0004 eV and 0.0022 eV for restricted singlet excitation energies, restricted triplet excitation energies, and unrestricted excitation energies, respectively; compared with the results calculated from the conventional spectral method. The application of PS‐FLR‐TDDFT to OLED molecules and organic dyes, as well as the comparisons for results calculated from PS‐FLR‐TDDFT and best estimations demonstrate that the accuracy of both PS‐FLR‐TDDFT and PS‐TDA‐TDDFT. Calculations for a set of medium‐sized molecules, including C_n fullerenes and nanotubes, using the B3LYP functional and 6‐31G^** basis set show PS‐TDA‐TDDFT provides 19‐ to 34‐fold speedups for C_n fullerenes with 450–1470 basis functions, 11‐ to 32‐fold speedups for nanotubes with 660–3180 basis functions, and 9‐ to 16‐fold speedups for organic molecules with 540–1340 basis functions compared to fully analytic calculations without sacrificing chemical accuracy. The calculations on a set of larger molecules, including the antibiotic drug Ramoplanin, the 46‐residue crambin protein, fullerenes up to C₅₄₀ and nanotubes up to 14×(6,6), using the B3LYP functional and 6‐31G^** basis set with up to 8100 basis functions show that PS‐FLR‐TDDFT CPU time scales as N^2.05 with the number of basis functions. © 2016 Wiley Periodicals, Inc.     

Effect of substituents on the absorption properties of three pyridylindolizine derivatives: A DFT and TDDFT study

Ground state properties and the UV–Vis absorption spectra of three recently synthesized pyridylindolizine derivatives have been studied by using density functional theory (DFT) and its time-dependent counterpart TDDFT. Performances of the two widely used hybrid functionals, B3LYP and PBE0, and of four different basis sets have been compared. The two functionals yield absorption spectra which have very similar shapes and characteristics but the excitations calculated with PBE0 are obtained at slightly shorter wavelengths. Basis sets affect the appearances of the calculated absorption spectra only little. Independent of the solvent polarity, simulation of the solvent effects by COSMO induces only slight changes into the ground state properties compared to those calculated in the gas-phase and into the absorption spectra.