PH2^+基态及低激发态的构型优化及光谱性质理论研究

本文报道了PH2^+的一组新的ab initio计算结果。给出了PH2^+的基态(X^1A1)及几个低激发态的电子结构和几何构型。这些态的稳定构型都是在MRSD CI水平上优化得到的。在此基础上, 确定了基态到这些低激发态的跃迁能和部分跃迁的振子强度和辐射寿命。     

S3分子的结构与最可几解离过程理论研究

用量子化学从头算方法,计算得到了S3分子优化的几何结构(基态和几个低激发态);研究了其在C2v与Cs群对称性下的解离过程,给出两种群对称性下基态和激发态的势能曲面及等高投影图;在两种群对称性下均得到在相应势能曲面上的优化的解离路径.     

芴与苯并硒化二唑共聚物的电子结构和光谱性质的理论研究

用密度泛函B3LYP方法对低聚体(DEF-BSeD)n(n=1~4)[其中9,9二乙基芴(DEF)单元与苯并硒化二唑(BSeD)单元的摩尔比分别为1∶1和2∶1]进行全优化, 计算电离能(PI)、电子亲和势(EA)和能隙(ΔH-L), 在基态结构的基础上用TD-DFT和ZINDO方法计算激发能和电子吸收光谱, 并利用外推法得到高聚物的相应性质. 从外推结果看出, 随着聚合物中BSeD比例的增大, 聚合物的最低单激发能呈减小的趋势, 最大电子吸收光谱红移. 用CIS方法优化得到单体的S1激发态结构, 计算结果表明, 激发态的结构更趋近于平面构型.     

BH分子X1∑+、A1∏和B1∑+态的势能函数

利用SAC/SAC-CI方法,使用D95++、6-311++g及cc-PVTZ等基组,对BH分子的基态(X1∑+)、第一简并激发态(A1∏)及第二激发态(B1∑+)的平衡结构和谐振频率进行了优化计算.通过对三个基组计算结果的比较,得出了cc-PVTZ基组为三个基组中的最优基组的结论;使用cc-PVTZ基组,利用SAC的GSUM(group sum ofoperators)方法对基态(X1∑+),SAC-CI的GSUM方法对激发态(A1∏和B1∑+)进行单点能扫描计算,用正规方程组拟合Murrell-Sorbie函数,得到了相应电子态的完整势能函数;从得到的势能函数计算了与基态(X1∑+)、第一简并的激发态(A1∏)和第二激发态(B1∑+)相对应的光谱常数(Be、αe、ωe和ωeXe),结果与实验数据较为一致.其中基态、第一激发态与实验数据吻合得较好.     

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.     

BH分子X~∑~+、A~1Ⅱ和B~1∑~+态的势能函数

利用SAC/SAC-CI方法,使用D95++、6-311++g及cc-PVTZ等基组,对BH分子的基态(X1撞+)、第一简并激发态(A1装)及第二激发态(B1撞+)的平衡结构和谐振频率进行了优化计算.通过对三个基组计算结果的比较,得出了cc-PVTZ基组为三个基组中的最优基组的结论;使用cc-PVTZ基组,利用SAC的GSUM(groupsumofoperators)方法对基态(X1撞+),SAC-CI的GSUM方法对激发态(A1装和B1撞+)进行单点能扫描计算,用正规方程组拟合Murrell-Sorbie函数,得到了相应电子态的完整势能函数;从得到的势能函数计算了与基态(X1撞+)、第一简并的激发态(A1装)和第二激发态(B1撞+)相对应的光谱常数(Be、琢e、棕e和棕e字e),结果与实验数据较为一致.其中基态、第一激发态与实验数据吻合得较好.     

马来酸酐均聚反应机理的理论研究Ⅰ: 马来酸酐的基态和激发态电子结构

用AM1方法计算了马来酸酐的基态和激发态电子结构、电荷分布和键级。马来酸酐基态分子的HOMO和LUMO分别是双键C=C的成键π-MO和反键π*-MO。从微观电子结构层次探讨了马来酸酐在不同条件下的均聚反应机理。计算结果能很好地阐明实验事实。     

ZnNe低激发态的量子化学研究

用相对论赝势ＣＡＳＳＣＦ／ＣＩ方法,对ＺｎＮｅ的基态和低激发态进行了计算,得出了它们的电子结构,势能曲线及光谱常数。计算结果表明,ＺｎＮｅ的基态分子是范德华分子,它的几个低激发态分子中的主要作用力为范德华力,这些态的分子仍为范德华分子。     

7-甲氧基香豆素-3-甲酰二乙醇胺的电子结构和光谱性质的理论研究

采用密度泛函的B3LYP和单激发组态相互作用(CIS)方法分别对基态和第一、第二单重激发态(S1和S2)结构进行优化,均采用6-31G(d)基组.在优化的基态和第一单重激发态的结构基础上,用含时密度泛函理论(TD-DFT),成功模拟了7-甲氧基香豆素-3-甲酰二乙醇胺的吸收光谱和荧光发射光谱,并用极化连续模型考虑了溶剂的影响.利用前线轨道、电荷密度差(CDD)和态密度(DOS)图分析了电子跃迁的特性.计算结果与实验结果吻合得很好.该量子计算方法对此类化合物的定性和定量研究是有效的.     

d8和d10配合物激发态性质和金属间弱相互作用的理论研究

随着量子化学理论方法和计算机技术的发展,量子理论模型已成为一种研究分子的高能、不稳定电子态-激发态的最有效手段.通过对一系列d8和d10配合物的激发态电子结构和电子激发前后金属相互作用的理论研究进行了评述.电子吸收和发射是极其复杂的微观过程,涉及到基态与激发态的电子结构性质、金属间弱相互作用、相对论效应等量子理论的基础问题,揭示配合物发光性质的规律性对新型光学材料的探索和设计具有重要指导意义.     

Theoretical investigations on geometrical and electronic structures of silver clusters

Geometrical structures and ground and excited states of silver clusters are theoretically investigated using long-range corrected (LC) density functional theory (DFT) calculations. The discrepancy between HOMO-LUMO gaps and the vertical ionization potential minus vertical electron affinity values, which should be the same values, is explored to reveal the significance of long-range exchange effects on the electronic states of metal clusters. The difference between HOMO-LUMO gaps and HOMO-LUMO excitation energies, which is called “exciton binding energy,” is also tested. As a result, it is found that the long-range exchange effects are requisite in DFT calculations to quantitatively investigate the ground and excited states of metal clusters. © 2018 Wiley Periodicals, Inc.     

Density functional theory study of 1,2‐dioxetanone decomposition in condensed phase

The decomposition of 1,2‐dioxetanone into a CO₂ molecule and into an excited state formaldehyde molecule was studied in condensed phase, using a density functional theory approach. Singlet and triplet ground and excited states were all included in the calculations. The calculations revealed a novel mechanism for the chemiluminescence of this compound. The triplet excitation can be explained by two intersystem crossings (ISCs) with the ground state, while the singlet excitation can be accounted by an ISC with the triplet state. The experimentally verified small excitation yield can then be explained by the presence of an energy barrier present in the potential energy surface of the triplet excited state, which will govern both triplet and singlet excitation. It was also found that the triplet ground state interacts with both the triplet excited and singlet ground states. A MPWB1K/mPWKCIS approach provided results in agreement with the existent literature. © 2012 Wiley Periodicals, Inc.     

The formation of nalidixic acid dimers and excimers in aqueous solutions

The influence of optical excitation on the formation of nalidixic acid dimers and excimers in aqueous media in the ground and excited states was studied. Quantum-chemical calculations of the total energy of monomers and dimers were performed. The spectral-luminescent characteristics of pairs of nlqH molecules were measured, and changes in charges on atoms in the ground and excited states were estimated.     

Synthesis, characterization, and spectroscopic investigation of benzoxazole conjugated Schiff bases

Two Schiff bases were synthesized by reaction of 2-(4'-aminophenyl)benzoxazole derivatives with 4-N,N-diethylaminobenzaldehyde. UV-visible (UV-vis) and steady-state fluorescence in solution were applied in order to characterize its photophysical behavior. The Schiff bases present absorption in the UV region with fluorescence emission in the blue-green region, with a large Stokes' shift. The UV-vis data indicates that each dye behaves as two different chromophores in solution in the ground state. The fluorescence emission spectra of the dye 5a show that an intramolecular proton transfer (ESIPT) mechanism takes place in the excited state, whereas a twisted internal charge transfer (TICT) state is observed for the dye 5b. Theoretical calculations were performed in order to study the conformation and polarity of the molecules at their ground and excited electronic states. Using density functional theory (DFT) methods at theoretical levels BLYP/Aug-SV(P) for geometry optimizations and B3LYP/6-311++G(2d,p) for single-point energy evaluations, the calculations indicate that the lowest energy conformations are in all cases nonplanar and that the dipole moments of the excited state relaxed structures are much larger than those of the ground state structures, which corroborates the experimental UV-vis absorption results.     

Theoretical study of the photoinduced transfer among the ground state and two metastable states in [Fe(CN)5NO]2-

Ab initio calculations were performed to investigate photoinduced transfers among the ground state (GS) and two metastable states (MS1 and MS2) of [Fe(CN)5NO]2-. We obtained the global potential energy surface of the electronic ground state by a scheme of multireference singly and doubly excited configuration interaction followed by a Davidson-type quadruple correction (MRSDCI+Q). The ground state surface has three local minima corresponding to GS, MS1, and MS2. The character of bond between Fe and the nitrosyl group are discussed. We carried out calculations of the lower five electronic excited states by MRSDCI+Q. The main configurations of these lower five excited states were represented by the dFe-->pi*NO transition accompanied by considerable back-donation. The potential energy surfaces of the six states, including the ground state, were obtained by state averaged complete active space self-consistent field calculations. The surfaces have several conical intersections and avoided crossings in the reaction pathway. The photoinduced transfers among GS, MS1, and MS2 are caused by the nonadiabatic effect near these crossings.     

Electronic Structures and Spectra of the Bases and Base Pairs of Nucleic Acids

The present paper covers electronic structures and spectra of the bases and the base pairs of nucleic acids calculated by using the INDO/S method. For free bases we give the energy levels of ground states and transition energies of low-lying excited states and discuss the band characters. The results indicate that the calculated spectra are in good agreement with experimental values. On the other hand, our calculations for A-T and G-C pairs are very beneficial to understanding hydrogen bond properties of these pairs.     

Solvent effect on the excited-state proton transfer of 7-hydroxyquinoline along a hydrogen-bonded ethanol dimer

We have studied the solvent effect on structures and potential energy surfaces along proton transfer in the ground and the excited states of 7-hydroxyquinoline interacting with an ethanol dimer using ab initio calculations. The proton transfer is forbidden in the ground state not only in vacuum but also in solvents of n-heptane, ethanol, and dimethyl sulfoxide. In the excited state, although the proton transfer is forbidden in vacuum, it is possible in solvent due to its greatly reduced barrier (～10 kcal mol(-1)) and highly stabilized product. It has also been found from the calculations that the proton-transfer barrier in the excited state decreases as the dielectric constant of a solvent increases. Our calculations are consistent with experimental results that the proton transfer does not take place in the ground state and that the excited-state proton-transfer rate increases as the solvent polarity increases. Our calculated absorption and emission properties are in excellent agreement with experimental results. Projection factors (reflecting geometrical change from the ground state to the excited state) and reorganization energies for several low frequency vibrations in connection with the excited-state proton transfer are discussed as well.     

CASSCF and CASPT2 studies on the structures, transition energies, and dipole moments of ground and excited states for azulene

The electronic structure of azulene molecule has been studied. We have obtained the optimized structures of ground and singlet excited states by using the complete active space self-consistent-field (CASSCF) method, and calculated vertical and 0-0 transition energies between the ground and excited states with second-order M?ller-Plesset perturbation theory (CASPT2). The CASPT2 calculations indicate that the bond-equalized C(2v) structure is more stable than the bond-alternating C(s) structure in the ground state. For a physical understanding of electronic structure change from C(2v) to C(s), we have performed the CASSCF calculations of Duschinsky matrix describing mixing of the b(2) vibrational mode between the ground (1A(1)) and the first excited (1B(2)) states based on the Kekule-crossing model. The CASPT2 0-0 transition energies are in fairly good agreement with experimental results within 0.1-0.3 eV. The CASSCF oscillator strengths between the ground and excited states are calculated and compared with experimental data. Furthermore, we have calculated the CASPT2 dipole moments of ground and excited states, which show good agreement with experimental values.     

铁原子与氮分子间的相互作用——单端位构型

用杂化密度泛函B3LYP方法在6-311+G(d)基组水平上研究了Fe 原子与N2分子相互作用的单端位构型的直线形和弯曲形两种结构的平衡几何结构、电子结构、轨道布局及红外光谱等性质. 计算结果表明, 由于强的σ-σ电子对互斥作用, 基组态4s²3d⁶的Fe原子不能与N2分子发生化学作用; 当Fe 原子呈现可与N2之间发生σ-π授予反馈作用的激发组态时, Fe 与N2分子之间可形成稳定的结构; 在得到的多个电子态中, 能量最低的是直线形的1³∑^-, 比Fe(a⁵D)和N2(¹∑⁺g )能量高21.6 kJ·mol-1, 同时存在几个能量相近的电子态, 如1³∏、1³Φ; 弯曲形都是不稳定态, 可能是连接直线形和单侧双配位构型的过渡态; 单端位构型产物相对于基态的反应物均是热力学不稳定的; 单端位构型中Fe对N2的活化作用很小, N—N 键长增加不超过7 pm.     

An ab initio study of the ground and low-lying excited states of the permanganate ion

The results of ab-initio self-consistent field calculations for the ground state and configuration interaction calculations for the excited states of the permanganate ion are presented and discussed. The calculations were performed using two large basis sets of contracted gaussian functions, and singly excited configurations were used in the calculations of the excited states. Fair agreement is obtained between these results and the experimental absorption spectra.