双核镉配聚物及其衍生物荧光光谱的密度泛函理论研究

采用DFT-B3LYP/6-31+G(d)方法,对配聚物[Cd2Cl4(Hbm)2]及其6种衍生物([M2-Cl4(HbmL)2],M=Zn2+,Hg2+;L=-CH3;-NH2;-CN)基态结构进行优化,用TD-DFT/B3LYP/6-31+G(d)方法计算其吸收光谱;同时用HF-CIS/6-31G(d)方法优化其最低激发单重态的几何结构,用含时密度泛函理论计算发射光谱.结果表明:电子在基态与激发态间的跃迁,主要是在卤素配体Cl到金属离子M的电荷转移(LMCL);发射光谱峰的计算最大值与实验值基本符合.改变中心金属离子M和咪唑环上的5位取代基可以精细地调控发光材料的光谱波段.     

第一激发态HOOO裂解反应的理论研究

利用量子化学方法对第一激发态HOOO的裂解反应进行了理论研究.所有驻点(反应物、产物和过渡态)的几何结构优化和振动分析都是在CASSCF/6-31 G(d,p)理论水平下进行的.反应路径上的选择点及驻点都在CASPT2/6-31 G(d,p)//CASSCF(19,13)/6-31 G(d,p)和MRCI/6-31 G(d,p)//CASSCF(19,13)/6-31 G(d,p)理论水平下进行单点能量校正.CASSCF,CASPT2和MRCI水平的理论计算结果显示,第一激发态HOOO的裂解反应包含一个对称性变化的过程.它首先通过了一个Cs对称性的过渡态,然后逐渐变化为线性结构,最终生成产物O2(3Σg-)和OH(2Π).     

2-(2-巯苯基)苯并噁唑分子内质子转移取代基电子效应的密度泛函理论研究

在B3LYP/6-31G(d,p)和TDB3LYP/6-31++G(d,p)//CIS/6-31G(d,p)水平上研究了2-(2-巯苯基)苯并噁唑及其衍生物基态和激发态分子内质子转移现象,并探讨取代基电子效应对分子内质子转移的影响,研究结果表明,在基态时,硫醇式异构体为优势构象,供电子取代基使基态分子内正向质子转移能垒(烯醇式→酮式)升高;而吸电子取代基则可降低能垒,有利于基态分子内质子转移并有助于硫酮式异构体的稳定.在激发态时,硫酮式结构为优势构象,所研究的2-(2-巯苯基)苯并噁唑化合物及衍生物均可以发生无能垒或低能垒(≤1.5kJ/mol)的激发态分子内质子转移.巯苯基部分是激发态失活的主要活性部分,供电子基团有利于激发态的质子转移,吸电子基团使激发态跃迁困难,不利于激发态的质子转移.     

2-(3-巯基-2-吡啶基)苯并咪唑分子内质子转移及溶剂化效应

在B3LYP/6-31G(d,p)和TD B3LYP/6-31++G(d,p)//CIS/6-31G(d,p)水平上,研究了2-(3-巯基-2-吡啶基)苯并咪唑(MPyBI)在气相和七种溶剂(环己烷、苯、三氯甲烷、乙醇、乙腈、二甲亚砜和水)中基态和激发态的分子内质子转移(GSIPT和ESIPT)过程.在基态势能面的研究中发现,该化合物存在分子内双质子转移,其中分步的双质子转移在动力学上具有优势.同时对激发态质子转移势能面及激发态转移过程中的光物理现象进行了研究,结果表明该化合物存在快速的无能垒的激发态分子内质子转移,随着溶剂极性的增强,可以降低基态过渡态的能垒,改变硫醇式与硫酮式互变异构体的比例,从而灵敏地控制荧光的强度.     

低硝酸盐离子N2O22-和亚硝酸HONO的异构体及其异构化反应的量化研究

采用Gaussian-98程序进行，在HF／6—31G(d)，B3LYP／6—31G(d)和MP2／6—31G(d)水平下优化分子结构并寻找过渡态，对于MP2／6—31G(d)结果在QCISD(T，E4T)，MP4／6—311 G(d，p)，MP4／6—311 G(2df，p)水平下重新计算能级．并用内禀反应坐标(IRC)法研究了N2O2^2-和亚硝酸HONO的异构化反应机理。     

8-巯基喹啉阴离子的锌配合物及其衍生物的电子光谱性质的含时密度泛函理论研究

采用从头算(ab initio)和密度泛函理论(DFT B3LYP)方法, 对配合物8-巯基喹啉锌Zn(tq)₂及其5种衍生物基态结构进行优化, 用含时密度泛函理论(TD-DFT/B3LYP)及6-31＋G(d)基组计算吸收光谱; 同时用ab initio HF 单激发组态相互作用(CIS)法在6-31G(d)基组上优化其最低激发单重态几何结构, 用含时密度泛函理论计算发射光谱. 结果表明, 电子在基态与激发态间的跃迁, 主要是在配体8-巯基喹啉(tq)环内的电荷转移, 电子从含S的苯硫酚环转移至含N的吡啶环上; 吸收光谱和发射光谱的计算值与实验值基本符合. 该类配合物都是优良的电子传输材料, 改变金属离子和取代基均可以调控发光材料的光谱波段.     

一种天然产物Wangzaozin A的细胞毒活性

从总序香茶菜Isodon racemosa (Hemsl) Hara植物中分离得到一个对人类肿瘤细胞Bel-7402和HD-8910具有毒活性的对映-贝壳衫烷型二萜Wangzaozin A化合物(1). 应用密度泛函理论(DFT)B3LYP方法, 对该分子的几何构型进行优化, 结果表明用B3LYP/6-31G(d)优化的几何参数与它的X射线衍射结构参数基本一致. 在优化的几何构型基础上, 采用规范不变原子轨道(GIAO)法, 在B3LYP理论水平分别用6-31G(d), 6-31G(d,p), 6-31+G(d,p)和6-31++G(d,p)基组进行核磁共振(NMR)化学位移值计算, 预测的1H和13CNMR化学位移值与实验值吻合; 统计误差分析表明, 用B3LYP/6-31G(d)优化的分子构型接近实际的分子构型. 因此, DFT方法适用这一类型化合物的构型和NMR参数进行预测. 在几何优化的基础上, 在B3LYP/6-31G(d)水平上, 对Wangzaozin A分子的静电位(MEP)进行理论计算. MEP三维图表明, 在Wangzaozin A分子中α-亚甲基环戊酮的羰基和羟基附近出现富电子区域(负电位), 起着供电子作用, 与受体的正电子区域结合. 这些结果从理论上支持了α-亚甲基环戊酮结构是一种抗肿瘤活性中心的看法.     

以二羧酸二苯甲醚和吡啶基三唑为配体构筑的钴(Ⅱ)配合物的合成、结构、热稳定性及DFT计算(英文)

基于V型配体4,4′-二羧酸二苯甲醚(H2oba)和刚性配体3-(3吡啶基)-5-(4′吡啶基)-1-H-1,2,4三唑(3,4′-Hbpt),在水热条件下与醋酸钴制备了一种新的配位聚合物[Co(oba)(3,4′-Hbpt)]·H2O,并对其进行X-射线单晶衍射、热重分析、元素分析和红外光谱表征。配合物为单斜晶系,P21/c空间群,完全脱质子的oba2-配体的2个羧基连接Co髤离子形成八元环,3,4′-Hbpt配体和H2oba桥连2个Co髤形成二十五元环。相邻的八元环和二十五元环进一步通过oba2-作支柱连接,形成了二维的层-孔结构。采用密度泛函理论(DFT)方法,在B3LYP/6-31*G(d)和6-31**G(d,p)水平上对配体H2oba结构进行优化计算,探讨了其稳定性,前线轨道以及最优构型,计算结果与化合物1中H2oba的构象一致。     

(CH2)2N和(CH3)2NH+的密度泛函理论计算

用密度泛函理论UB3LYP／6-31G（d,p）方法研究了二甲胺自由基（CH3）2N及其质子化离子（CH3）2NH 的构象和超精细结构．在由构象研究得到的两种自由基的最稳定结构上,用密度泛函的UB3LYP和UB3PW91方法及从头计算的UHF、UMP2（FULL）方法计算了α-质子、β-质子和N核上的超精细偶合常数A（Hα）、A（Hβ）和A（N）结果表明：两种自由基中甲基内旋转的位垒均很低,分别为0．46kJ·mol-1（（CH3）2NH ）和2．6kJ·mol-1（（CH3）2N）．UB3LYP／6-31G（d,p）和UB3PW91／6-31G（d,p）计算的A（Hα）、A（Hβ）和A（N）与ESR实验结果符合得很好,UMP2／6-31G（d,p）方法的计算值与实验值符合得也较好．     

单重态CCl2与O3反应机理的理论研究

用量子化学从头算方法,研究了单重态CCl_2与O_3反应的机理.在HF/6-31G(d)水平上用梯度解析技术全参数优化上述反应的反应物、中间体、过渡态和产物构型,MP2/6-31G(d)//HF/6-31G(d)方法计算能量.给出了有关化合物的结构数据.结果表明:CCl_2与O_3首先生成富能中间体CCl_2O_3,然后中间体裂解生成CCl_2O和O_2.该反应为强放热反应,放出的热量为516.88kJ·mol~(-1)[MP2/6-31G(d)//HF/6-31G(d)].通过内禀反应坐标(IRC)计算,获得了沿反应途径的势能剖面.     

Neutral homoaromaticity in some heterocyclic systems

[reaction: see text] Neutral homoaromaticity has been evaluated in heterocyclic systems related to the bicyclo[3.2.1]octane skeleton with replacement of CH(2) at C-2 in bicyclo[3.2.1]octa-3,6-diene with X = BH, AlH, Be, Mg, O, S, PH, NH (12); replacement of CH at C-3 in bicyclo[3.2.1]octa-3,6-dien-2-yl anion with PH, S, NH, O (13); and replacement at C-2 and C-3 with N and O (14). Stabilization energies (SE) are evaluated using density functional theory and homodesmotic equations at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level for series 12-14. Stabilization energies are compared with diamagnetic susceptibility exaltations, Lambda, CSGT-B3LYP/6-31G(d)//B3LYP/6-31G(d), and nucleus-independent chemical shifts (NICS), GIAO-B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d). Analysis of frontier orbitals and geometries, B3LYP/6-31G(d)//B3LYP/6-31G(d), and proton affinities of 2-azabicyclo[3.2.1]octa-3,6-diene, pyrrole, and related model systems, B3LYP/6-311+G(2d,2p)//B3LYP/6-31G(d), provide complementary evidence supporting the division of the substrates evaluated into antihomoaromatic (12, X = BH, AlH, and Be), nonhomoaromatic (12, X = O, S, NH, PH), and homoaromatic (13, X = S, PH, NH, O and 14 X = ON), with 12 (X = Mg) appearing as transitional between anti- and nonhomoaromatic.     

Environmental photochemistry of nitro-PAHs: direct observation of ultrafast intersystem crossing in 1-nitropyrene

Femtosecond broadband transient absorption experiments of 1-nitropyrene, a nitro-polycyclic aromatic hydrocarbon of environmental concern are presented in cyclohexane and hexane solutions. The transient absorption spectra show the presence of three species that are assigned to the Franck-Condon excited lowest singlet (S1) state, the structurally relaxed S1 state, and the lowest excited triplet state. The spectral changes at early times are interpreted in terms of conformational dynamics; primarily due to an ultrafast rotation of the nitro group in the S1 state. This excited state relaxation is followed by intersystem crossing with a time constant of 7 ps. CIS/6-31G(d,p) calculations predict planarization of the nitro-aromatic torsional angle as the major nuclear relaxation coordinate, from 32.8 degrees at the HF/6-31G(d,p) level of theory in the ground state (27.46 degrees at B3LYP/6-31++G(d,p)) to 0.07 degrees in the S1 state. Vertical excitation energies at the TDDFT/6-31++G(d,p) and TDDFT/IEFPCM/6-31++G(d,p) levels of theory predict a small energy gap (<0.12 eV) between the S1(pipi*) state and the third excited triplet state T3(npi*) in the gas phase and in cyclohexane, respectively. The small energy gap suggests a large spin-orbit coupling between the S1(pipi*) and T3(npi*) states, which explains the ultrafast intersystem crossing of 1-nitropyrene in nonpolar solvents.     

Prediction of the 13C NMR Chemical Shifts of Fluorenone Analogues by the GIAO Method

After the geometry optimization at B3LYP/6-31+G(d,p) level,the NMR calcula-tions of a series of fluorenone analogues have been carried out by GIAO method at HF/6-31+G(d) level and B3LYP/6-311G+(2d,p) level,respectively.The 13C NMR chemical shifts calculated at HF/6-31+G(d) level show better agreement with the observed values.By a series of linear correction equations (δpred=a + bδcalc),accurate prediction of 13C chemical shifts was achieved for the new fluorenone compound.The linear correlation of δpred with δexptl is excellent,and the square of correlation coefficient,r2,is up to 0.994.The maximum absolute difference between δpred and δexptl,Δδ,is 4.6 ppm,and the root-mean-square error between δpred and δexptl is only 2.6 ppm.     

DFT study of the electronic and charge transfer properties of perfluoroarene–thiophene oligomers

The ground state structures of 5,5″-diperfluorophenyl-2,2′:5′,2″:5″,2‴-quaterthiophene (1), 5,5′-bis{1-[4-(thien-2-yl)perfluorophenyl]}-2,2′-dithiophene (2), 4,4′-bis[5-(2,2′-dithiophenyl)]-perfluorobiphenyl (3), 5,5″-diperfluorophenyl-2,2′:5′,2″-tertthiophene (4), 5,5′-diperfluorophenyl-2,2′-dihiophene (5), and 5,5-diperfluorophenylthiophene (6) have been optimized at the B3LYP/6-31G(d), B3LYP/6-31G(d,p), PBE0/6-31G(d), and PBE0/6-31G(d,p) level of theories. The B3LYP/6-31+G(d) and PBE0/6-31+G(d) level of theories have been applied to investigate the absorption spectra. The PBE0 functional is good to predict the C–S bond lengths while the C–F bond lengths are good envisaged with B3LYP functional. The increment of thiophene rings between two perfluoroarene rings leads to red shift in absorption spectra. The electron affinities are energetically destabilized while energetic stabilization of the radical-cation increases by decreasing the thiophene rings from four to one. The perfluoroarene rings leads to enhance the electron injection.     

NMR spectra, GIAO and charge density calculations of five-membered aromatic heterocycles

The B3LYP/6-31+G(d) molecular geometry optimized structures of 17 five-membered heterocycles were employed together with the gauge including atomic orbitals (GIAO) density functional theory (DFT) method at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p) and B3LYP/6-311+G(2d,p) levels of theory for the calculation of proton and carbon chemicals shifts and coupling constants. The method of geometry optimization for pyrrole (1), N-methylpyrrole (2) and thiophene (7) using the larger 6-311++G(d,p) basis sets at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,p) and B3LYP/cc-pVTZ levels of theory gave little difference between calculated and experimental values of coupling constants. In general, the (1)H and 13C chemical shifts for all compounds are in good agreement with theoretical calculations using the smaller 6-31 basis set. The values of nJHH(n=3, 4, 5) and rmnJ(CH)(n=1, 2, 3, 4) were predicted well using the larger 6-31+G(d,p) and 6-311++G(d,p) basis sets and at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,2p) levels of theory. The computed atomic charges [Mülliken; Natural Bond Orbital Analysis (NBO); Merz-Kollman (MK); CHELP and CHELPG] for the B3LYP/6-311++G(d,p) geometry optimized structures of 1-17 were used to explore correlations with the experimental proton and carbon chemical shifts.     

Quantum chemical calculations based on ONIOM and the DFT methods in the inclusion complex: doxycycline/2-O-Me-β-cyclodextrin

A computational study of inclusion complexes of 2-methyl-βCD with Doxycycline tautomeric (enol and keto form) has been performed with several combinations of ONIOM hybrid calculations. The reliability of the ONIOM2 calculations at the integrated level, ONIOM2 (M05-2X/6-31G(d): M05-2X/3-21G*), ONIOM2 (M05-2X/6-31G(d):HF/3-21G*), ONIOM2 (B3LYP/6-31G(d):HF/3-21G*), ONIOM2 (B3LYP/6-31G(d):B3LYP/3-21G*) and ONIOM2 (B3PW91/6-31G(d):B3PW91/3-21G*) was examined. Their complexation, binding, deformation and stabilization energies, and geometrical data were compared with those of the target geometry structure optimized at the M05-2X/6-31G(d) level of theory. Mixed combinations ONIOM2 (M05-2X 6-31G(d):HF 3-21G*) and ONIOM2 (B3LYP 6-31G(d):HF 3-21G*) reproduces nearly the target geometry structure and provides realistic energetic results at a relatively low computational cost.     

Vitamin E models. Conformational analysis and stereochemistry of tetralin, chroman, thiochroman and selenochroman

Tetralin, chroman as well as its' S and Se containing congeners were subjected to ab initio (RHF/3-21G and RHF/6-31G(d)) and DFT (B3LYP/6-31G(d)) computation. Molecular geometries and the activation energies for ring inversions were determined with full geometry optimizations.     

Quantum Chemical Study of the Lithium Cation Coordination by Dimethylsulfoxide Molecules

A quantum chemical study of the lithium ion coordination by dimethylsulfoxide molecules has been performed by HF/6-31G (d), HF/6-311+(d,p), and B3LYP/6-311+(d,p) methods with full geometry optimization. The coordination number of Li⁺ in the dimethylsulfoxide was found to be equal to 4. Heats of the complex formation at each stage of the process were calculated (in kJ/mol); these are 267.2, 203.0, 122.8, and 90.5 in HF/6-31G(d); 270.6, 200.5, 108.8, and 82.9 in HF/6-311+(d,p); 256.3, 186.8, 100.8, and 80.1 in B3LYP/6-311+(d,p) for 1-4 DMSO molecules, respectively. The paper reports on the structure parameters of the complexes formed, and the corresponding charge distributions. The solvation of the lithium cation with dimethylsulfoxide molecules was shown to be more preferable than that with water molecules in the gas phase. A possibility for an Li⁺·(4DMSO)·OH^- associate to form in the DMSO medium was examined using the HF/6-311+(d,p) method.     

Comparison of Some Computational Methods for Geometry Optimisation of Phosphorus Acid Derivatives

Several economical methods for geometry optimization, that should be applicable to larger molecules, have been evaluated for 19 phosphorus acid derivatives. MP2/cc-pVDZ geometry optimizations are used as reference points and the geometries obtained from the other methods are evaluated with respect to deviations in bond lengths and angles, from the reference geometries. The geometry optimization methods are also compared to the much used B3LYP/6-31G(d) method. Single point energies obtained by subsequent EDF1/6-31+G(d) or B3LYP/6-31+G(d,p) calculations on the respective equilibrium geometries are also reported relative to the energies obtained from the reference geometries. The geometries from HF/MIDI! optimizations were closer to those of the references than the geometries of the HF/3-21G(d), HF/6-31G(d), and B3LYP/MIDI! optimizations. The EDF1/6-31+G(d) or B3LYP/6-31+G(d,p) single point energies obtained from the HF/3-21G(d), HF/6-31G(d), and B3LYP/MIDI! geometries gave a mean absolute deviation (MAD) from that of the reference geometries of 1.4-3.9 kcal mol m 1 . The HF/MIDI! geometries, however, gave EDF1/6-31+G(d) and B3LYP/6-31+G(d,p) energies with a MAD of only about 0.5 and 0.55 kcal mol m 1 respectively from the energies obtained with the reference geometries. Thus, use of HF/MIDI! for geometry optimization of phosphorus acids is a method that gives geometries of near-MP2 quality, resulting in a fair accuracy of energies in subsequent single point calculations, at a much lower computational cost other methods that give similar accuracies.