Reinvestigation of photoinduced intramolecular charge transfer reaction in p-Dimethylaminobenzaldehyde by spectroscopic method and Density Functional Theory (DFT) calculation

The excited state charge transfer (CT) properties of p-Dimethylaminobenzaldehyde (DMABA) have been reinvestigated spectroscopically in combination with quantum chemical calculations. The molecule having weak acceptor group (–CHO) shows weak charge transfer emission, which follows linear dependency on solvent polarity parameters and E_T(30) values. However, previously reported CT emission of DMABA in ACN and in DMF solvents by Grabowski et al. (Chem. Rev. 103 (2003) 3899) and Kawski et al. (Chem. Phys. Lett. 448 (2007) 208) are ambiguous and are different from the Grabowski's previous studies (Pure Appl. Chem. 55 (1983) 245) and the present results. Theoretical potential energy surfaces along both the donor and acceptor twisting motion using Density Functional Theory (DFT) with B3LYP functional and 6-311++G^?? basis set following Twisted Intramolecular Charge Transfer model support our experimental results. Time Dependent Density Functional Theory Polarization Continuum Model (TDDFT-PCM) has been used to explore the solvent effect on the emission spectra of DMABA.     

Unfolding ESIPT in Bis-2,5-(2-benzoxazolyl) Hydroquinone and 2,5-Bis(benzo[d]oxazol-2-yl)-4-methoxyphenol: a Comprehensive Computational Approach

The photo-physical behaviour of bis-2,5-(2-benzoxazolyl) hydroquinone and 2,5-bis (benzo[d]oxazol-2-yl)-4-methoxyphenol was studied using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT). All the possible rotamers were optimized to obtain global minimum optimized structure. The theoretical absorption and emission values of rotamers estimated by using TD-DFT [TD-B3LYP/6–31G(d)] are in good agreement with experimental absorption and emission wavelengths. Based on the absorption values, the contribution of respective rotamer is determined theoretically.     

Theoretical modelling of encapsulation of the Altretamine drug into BN(9,9-5) and AlN(9,9-5) nano rings: a DFT study

The aim of this paper is a better comprehension of the encapsulation and interaction an anticancer drug Altretamine into BN nano ring [BNNR(9,9-5)] and AlN nano ring [AlNNR(9,9-5)]. The electronic and adsorption properties of the molecule Altretamine over the BNNR and AlNNR were theoretically studied in the solvent phase at the B3LYP/6-31G* level of theory for the first time. With the non-bonded interaction of Altretamine, the electronic properties of the BN and AlN nano-cages can be significantly changed. The electronic spectra of the Altretamine drug, complex BNNR/Altretamine and AlNNR/Altretamine in solvent water were calculated by Time Dependent Density Functional Theory (TD-DFT) for the investigation of adsorption effect. According to the natural bond orbital (NBO) results, the molecule Altretamine, BNNR and AlNNR play as both electron donor and acceptor at the complexes BNNR/Altretamine and AlNNR/Altretamine. On the other hand, the charge transfer is occurred between the bonding, antibonding or nonbonding orbitals in the molecule drug, BNNR and AlNNR. As a consequence, BNNR(9,9-5) and AlNNR(9,9-5) can be considered as a drug delivery system for the transportation of Altretamine as anticancer drug within the biological systems.     

Excited State Lactim to Lactam Type Tautomerization Reaction in 5-(4-Fluorophenyl)-2-Hydroxypyridine: Spectroscopic Study and Quantum Chemical Calculation

The photophysical properties of 5-(4-fluorophenyl)-2-hydroxypyridine (FP2HP) have been studied by steady state and time resolved spectroscopy in combination with quantum chemical calculations. The molecule FP2HP exists as lactim and lactam form in the ground state due to small stability difference but does not undergo lactim to lactam isomerisation due to high barrier energy. Whereas in the excited state the lactim form undergoes tautomerization producing red shifted emission of the lactam tautomer along with the local emission of the lactim form. In polar protic solvents, the barrier for lactim-lactam tautomerization rapidly decreases forming the lactam tautomer only. Temperature has pronounced effect on the excited state tautomerization equilibrium and is clearly reflected in the measured equilibrium constant (K _tau ⁰ ) and free energy change (??G⁰). Structural calculations at Hartree Fock and Density Functional Theory levels, calculated stability of the isomers in different solvents using Polarized Continuum Model and the theoretical potential energy surfaces for the ground and excited states along the proton transfer coordinate are reported for the tautomeric equilibrium of FP2HP.     

New Aspects of Enhancing the Graphene Capacitance by Defects in Aqueous Electrolytes and Ionic Liquids

JETP Letters - The influence of internal and external defects in graphene on the capacitance of the graphene/electrolyte interface was explored using Density Functional Theory (DFT) calculations....     

TDDFT Investigation of the Electronic Structures and Photophysical Properties of Fluorescent Extended Styryl Push-Pull Chromophores Containing Carbazole Unit

Push-pull chromophores attached to carbazole based π-conjugating spacers bearing N-alkylamino donors, cyanovinyl and carbethoxy acceptors have been studied by the means of UV-Visible measurements. The intramolecular charge transfer (ICT) of these π-conjugated systems has also been tested by investigating the ability of the solute molecules to undergo shifts in their fluorescence emission maxima with increasing solvent polarity. Density Functional Theory [B3LYP/6-31G(d)] and Time Dependent Density Functional Theory [TD-B3LYP/6-31G(d)] computations have been used to have more understanding of the structural, molecular, electronic and photophysical parameters of push-pull dyes. The largest wavelength difference between the experimental and computed electronic absorption maxima was 45 nm. For emission, a largest difference of 61 nm was observed. The ground state and excited state dipole moments in different solvents were determined using experimental solvatochromic data and computed Onsager radii. The dipole moments of the molecules in the excited state were observed to be higher than in the ground state.     

Tetrathia- and tetraselenafulvalene adsorbed on Ag(110): A theoretical study

We have studied the adsorption properties of the π-donor molecule TXF, where X stands for the chalcogens sulfur and selenium [TTF = tetrathiafulvalene, TSF = tetraselenafulvalene], respectively, on the (110) surface of silver by means of periodic plane-waves based DFT (Density Functional Theory) calculations using slab models. We have determined and characterized the stable adsorption sites and have evaluated the charge transfer from TXF molecules into the surface. The simulation of the vibrational spectra for TXF and the fully deuterated TXF species has permitted to identify the fingerprints of both molecules on this surface.     

Electronegativity of fractionally charged atoms in the Density Functional Theory

The electronegativity (identified with the negative of the chemical potential) of atoms and ions has been calculated in several isoelectronic series using the Density Functional Theory. Then, the electronegativities of atoms and ions with fractional nuclear charge have been obtained by interpolation in each isoelectronic series. Similar interpolations have been performed, starting with approximate electronegativities obtained by Mulliken's finite difference approximation. Both sets of results have been compared.     

2-(2-吡啶基)苯并咪唑配合物的合成及发光

选用了具有代表性的过渡金属元素Cd、Zn以及主族元素Ca、Mg作为中心金属离子,合成了基于2-(2-吡啶基)苯并咪唑(PBM)配体的系列金属配合物。实验数据表明这些配合物是一类具有高的荧光量子产率并且化学性质稳定的蓝色发光材料。 研究了该类配合物的光致发光性质以及中心金属离子半径大小对配合物发射峰位的影响,比较了中性配合物、配阳离子型配合物的发光性质以及这类金属离子微扰配体发光受其因素的影响。     

Electronic properties of Li-doped zigzag graphene nanoribbons

Zigzag graphene nanoribbons (ZGNRs) are known to exhibit metallic behavior. Depending on structural properties such as edge status, doping and width of nanoribbons, the electronic properties of these structures may vary. In this study, changes in electronic properties of crystal by doping Lithium (Li) atom to ZGNR structure are analyzed. In spin polarized calculations are made using Density Functional Theory (DFT) with generalized gradient approximation (GGA) as exchange correlation. As a result of calculations, it has been determined that Li atom affects electronic properties of ZGNR structure significantly. It is observed that ZGNR structure exhibiting metallic behavior in pure state shows half-metal and semiconductor behavior with Li atom.     

Quantum Chemical Calculations on 4-[2-(Tert-Butylamino)-1-Hydroxyethyl]-2-(Hydroxymethyl)Phenol by Density Functional Theory

Density functional theory (DFT) calculations have been carried out for the compound 4-[2-(tert-butylamino)-1-hydroxyethyl]-2-hydroxymethyl) phenol (4BAHEHMP) by using the B3LYP method at the 6-311++G (d,p) basis set level. The electric dipole moment (μ) and the first hyperpolarizability (α) values of the investigated molecule were computed. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (COOP or OPDOS) diagrams analysis were presented. HOMO and LUMO energies confirm that charge transfer occurs within the molecule. In addition Molecular Electrostatic Potential (MEP), Natural Bond Orbital analysis (NBO) and Non- Linear Optical (NLO) properties are studied.     

硫原子在镍基合金825(001)面吸附的第一性原理研究

元素硫在镍基合金表面吸附产生严重的电化学腐蚀,为从原子尺度研究硫腐蚀机理,采用第一性原理方法,构建并优化了镍基合金825的晶胞结构模型,计算分析了S原子在镍基合金825耐蚀性较差面(001)晶面的吸附及电子转移情况.结果表明:Ni原子占据顶角, Cr原子和Fe原子对称占据面心是镍基合金825稳定的晶胞结构;原子S在镍基合金825(001)面上最稳定的吸附位为四重穴位,吸附能为-6.51 eV; S吸附前后的态密度(DOS)和二维电荷差分密度图(DCD)对比发现,镍基合金825中Fe与S之间电荷偏移明显,形成离子键,易生成腐蚀产物Fe_xS_y. S的吸附对镍基合金825中Cr原子的电子分布影响不大,且合金中Cr和Ni抑制了合金中Fe与S之间的相互作用,从而提高了合金耐蚀性.     

Vibrational Spectroscopic Study of N-[4-[1-Hydroxy-2-[(1-Methyl Ethyl) Amino] Ethyl] Phenyl] Methane Sulfonamide

The vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 4 000～400 and 4 000～400 cm-1 respectively, for N-[4-[1-hydroxy-2-[(1-methyl ethyl) amino] ethyl] phenyl] methane sulfonamide (HPAEPMS) molecule. Theoretical calculations were performed by ab initio Density Functional Theory (DFT) method using 6-31G(d,p) basis set. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement.     

On the nature of trapped states in an MoS2 two-dimensional semiconductor with sulfur vacancies

ABSTRACT

Molybdenum disulfide (MoS₂) is a common two-dimensional semiconductor that has been highly studied as an emerging material for catalysis and electronics. The most common material defects in MoS₂ are sulfur vacancies. In order to reveal the nature of the trapped states induced by sulfur vacancies, we perform Density Functional Theory (DFT) combined with quantum dynamics calculations. According to our model, we find that the sulfur vacancies create trap states in the original band gap of monolayer MoS₂ that disrupt charge transmission through the monolayer. In addition, we did not find any resonance states among the shallow states in the conduction band continuum.     

Spectroscopic Studies of a New Multi-Element Sensitive Fluorescent Probe Derived from 2-(2-pyridyl)benzimidazole: Selective Discrimination of Zn2+ from Its Congeners

ABSTRACT

A new multielement sensitive fluorescent probe, 1-(2-(phenylthio)ethyl)-2-(pyridin-2-yl)-1H-benzo[d]imidazole (L), has been synthesized by the reaction between 2-(pyridyl) benzimidazole and 2-chloroethyl phenyl sulfide. Excitation and emission wavelength of L are at 330 and 371 nm, respectively. Among various transition and nontransition metal ions, it can selectively read Zn²⁺ ion as the emission wavelength of L undergoes a red shift by 31 nm upon binding with Zn²⁺ in methanol. In the presence of Cd²⁺, Hg²⁺, and other common cations, the emission wavelength of L remains unchanged, and thus allows us to discriminate Zn²⁺ from its congeners. Both L and its Zn²⁺ complex are well characterized by different spectroscopic techniques like ¹H-NMR, ESI-TOF (+) mass, FT-IR, and elemental analysis data. The binding constant value of the complexation reaction between L and Zn²⁺ is found as 724.6 M^?1 in methanol. Density functional theoretical (DFT) studies nicely demonstrate the red shift in the emission wavelength of L upon binding with Zn^2+.     

2-(3’,4’-二羧基苯氧基)苯甲酸配体桥联的锌(Ⅱ)配合物的合成、结构及荧光性质

以2-(3’,4’-二羧基苯氧基)苯甲酸(H3DPBA)和1,3-二(4-吡啶基)-丙烷(bpp)为配体,与Zn(Ac)2通过水热反应,获得了一维链状配合物Zn(DPBA)(bpp)。该配合物的一个不对称单元包括一个Zn(Ⅱ)离子,一个DPBA配体和一个bpp配体。Zn(Ⅱ)离子与四个氧原子及一个氮原子配位,其配位数为5。固态配合物在375nm处出现强的发射峰,来自于配体的π~*—π跃迁。与配体的荧光发射光谱比较,配合物的荧光发射峰发生了蓝移,而且配合物的荧光发射强度有大幅度增强。讨论了配合物在常见溶剂中和金属阳离子中的荧光性质。实验结果表明不同有机小分子或不同金属阳离子对配合物的荧光强度有不同程度的影响,有机小分子硝基苯和Fe~(3+)使配合物荧光猝灭,该Zn(Ⅱ)-配合物可用于硝基苯的检测以及水和乙醇体系中Fe~(3+)的检测。     

水分子辅助的一碳单元转移机理的密度泛函研究

为验证甘氨酰胺转甲酰基酶 (Glycinamideribonucleotidetransformylase ,GARTfase)催化的一碳单元转移反应是嘌呤“从头合成”过程中一个关键步骤的实验推测 ,用B3LYP方法 ,在 6 31G 基组水平上研究了GARTfase催化反应中水分子辅助的一碳单元转移机理 .该反应一共有两条可能的反应通道 :协同的 (patha)和分步的(pathb) ,计算表明 ,后者具有较低势垒 ,更占优势 .计算结果较好地证实了实验假设 ,并进一步表明 :水分子的参与能够缓解体系的张力 ,更有利于一碳单元转移反应的进行 .     

Indole-Based NLOphoric Donor-π-Acceptor Styryl Dyes: Synthesis,Spectral Properties and Computational Studies

Donor-π- acceptor styryl chromophores based on indole core were synthesized by Knoevenagel condensation of N-ethyl indole-3-carbaldehyde and different active methylene compounds. The absorption and emission properties of these dyes in different solvents were studied. The dyes displayed a broad absorption maximum in the UV and visible region between 397 and 469 nm with FWHM, 50 to 75 nm. Due to the extended π – conjugated systems this styryl chromophores shows strong intramolecular charge transfer characteristics. The dyes showed solid state emission and emission in solid state was red shifted as compared to their emission in less polar solvents. Density Functional Theory [B3LYP/6–311 + G(d)] computations were used to correlate the structural, molecular, electronic and photo physical parameters of styryl dye with experimental study. Synthesized dyes were confirmed by using FT-IR, ¹H NMR, ¹³C NMR and HRMS spectral analysis.     

姜油细胞原位拉曼光谱研究

提出一种用拉曼光谱原位分析新鲜姜油细胞中姜油主成分的方法。用徒手切片制备新鲜姜样品,该样品置于DXR 激光共焦显微拉曼光谱仪下,用20倍物镜观察到油细胞,将激光聚焦在该油细胞上,获得了姜油细胞中姜油的拉曼光谱,共21条谱峰。不同油细胞上获得的拉曼光谱非常相似。获得了姜精油的拉曼光谱,与姜精油拉曼光谱的37条谱峰比较,油细胞有19条谱峰与之有对应关系。为了解释油细胞精油及姜精油的拉曼光谱,用密度泛函理论计算了姜烯的拉曼光谱。姜精油拉曼光谱有31条谱峰,油细胞中有19条谱峰与计算光谱有对应关系。该研究提供了一种拉曼光谱技术与密度泛函理论计算结合的快速容易的精油质量控制方法。