1,2,3-三氮杂苯-水复合物氢键相互作用

用密度泛函理论在B3LYP/6-31 G**水平上对1,2,3-三氮杂苯和水形成1:1、1:2和1:3复合物的基态氡键结构进行几何优化和性质计算．计算结果表明,复合物之间存在较强的氢键作用．所有稳定复合物结构中形成一个N…H-O氢键并终止于O…H-C氢键的氢键水链构型最稳定．氢键的形成是水分子中H-O键振动频率减小(红移)．NBO分析表明,最稳定的1:1、1:2和1:3复合物发生分子间电荷转移总量分别为0．0222e、0．0261e和0．0273e．同时,用含时密度泛函理论方法在TD-B3LYP/6-31 G**水平计算了1,2,3-三氮杂苯单体及其氢键复合物的第一1(n,π*)激发态的垂直激发能．     

1,3,5-三氮杂苯－水簇氢键结构性质

在B3LYP/6-31 G**和MP2/6-31 G**水平上对1,3,5-三氮杂苯-(H2O)n(n=2,3)复合物的基态氢键结构进行几何优化和性质计算,结果表明复合物之间存在较强的氢键相互作用,所有稳定复合物结构中形成一个N…H-O氢键并终止于弱O…H-C氢键的氢键水链构型最稳定.氢键的形成是水分子中H-O键振动频率减小(红移).NBO分析表明,最稳定的1:2和1:3复合物发生分子问电荷转移总量分另q为0.02501 e和0.02777 e.     

1-甲基萘的振动分辨激光诱导荧光光谱研究

在超声射流条件下得到了1-甲基萘的激光诱导荧光光谱,并结合理论计算研究了1-甲基萘分子的基态和激发态的几何构型及振动信息.运用DFT方法在B3LYP/6-311++G*的水平上优化了1-甲基萘的基态儿何构型,结果表明1-甲基萘分子基态的S-E和E-S两个构象体中,只有S-E构象体为稳定构型,E-S构象是连接两个S-E构...     

溶剂化对有机给、受体分子热激活延迟荧光的影响及调控EI北大核心CSCD

具有热激活延迟荧光(Thermally activated delayed fluorescence,TADF)特性的有机给、受体(Donor-acceptor,D-A)分子体系通过反向系间窜越捕获三重态激子,可以将内量子效率的理论上限提高到100%,因而受到极大关注。通常,具有分子内电荷转移特性的D-A体系可以通过构建扭曲的分子构象来减小单、三重态之间的能差ΔES-T,以确保反向系间窜越快速发生。当分子被激发后,若激发态构象中D-A的二面角更接近90°时,ΔES-T会更小,延迟荧光也会增强。然而,快速的溶剂化过程常常会影响激发态构象、分子内电荷转移过程、延迟荧光发射,这使得研究TADF分子发光过程更富有挑战。本文综述了本课题组近期在溶剂化对D-A体系延迟荧光的影响及调控方面所取得的初步进展。结果显示,强极性溶剂会导致非辐射弛豫增加,不利于TADF发射;改变溶剂粘度会影响激发态构象弛豫,从而可以实现对TADF的增强或减弱的调控。这些结果有助于理解溶剂化效应与构象弛豫、TADF之间的关系,为TADF分子的设计与合成提供指导。     

胸腺嘧啶-BH3构型与性质的DFT和MP2研究

对胸腺嘧啶 BH3复合物分别用B3LYP/6 31G(d)和MP2/6 31G(d)进行计算,以预测该复合物的构型 及结合能,得到了5种构型,并进行了振动分析和自然键轨道分析.对各构型进行了更大基组(6 311+G(2df)和 aug cc pVDZ)的单点能量计算.结果表明,B原子与O原子直接相连的构型(a)、(b)比较稳定,其结合能为90.4 和88.0kJ/mol(B3LYP/6 31G(d),BSSE校正).N原子向B原子的空轨道提供电子形成构型(c)和(d),只找到 了一种由C原子向B原子提供π电子的构型(e).所有构型中均存在电荷授受,各构型的结合能与电荷转移量有 良好的相关性.复合物的形成,使其红外光谱均有不同程度的红移,红移幅度与复合物的稳定性相关.     

2''-脱氧鸟苷在水溶液中激发态氢键动力学的密度泛函理论研究

用密度泛函理论和含时密度泛函理论研究了2'-脱氧鸟苷在水溶液中形成的一水和二水复合物在基态和激发态的氢键性质．计算了两种复合物的稳定构型、红外光谱、前沿分子轨道以及密里根电荷等光物理参数．结果表明,两种水合物的分子内氢键在光激发下变化不一致,分子间氢键变化相似．一水复合物的分子内氢键N3···H4-O2 在激发态是加强的,二水复合物的是减弱的．两种水合物的分子间氢键N2-H2···O3和O3-H5···O2及O3···H7-O4和H5···O1-C1在激发态全是减弱的．两种复合物红外光谱的计算结果与实验值一致．二水复合物中分子间氢键O4···H1-N1在激发态断裂,形成了新的分子间氢键O4···H3-N2,这种变化可能与鸟嘌呤部分的结构弯曲有关．最后分析了一水和二水复合物分子的分子内电子转移特性．     

CuCl催化下苯炔与环己烯乙炔偶联反应机理的理论研究

利用密度泛函理论(DFT)研究了Cu Cl催化下苯炔与环己烯乙炔偶联反应的微观反应机理.在B3LYP/6-31+G*基组水平上(Cu采用了赝势基组Lan L2DZ)优化了反应过程中所有化合物的几何构型并计算了频率,通过能量、频率和振动方式确定了中间体和过渡态的真实性.此外,在同等基组水平上还运用了分子中的原子理论讨论了成键临界点的电荷密度的变化,运用了自然键轨道理论讨论了键的性质与轨道间的相互作用.为了提高计算精度,在6-311+G*基组水平上计算了反应机理中所有物质在气相及溶剂化下的单点能,得到与6-31+G*基组计算相同的结论.结论表明Cu Cl对苯炔与1-乙炔基环己烯偶联反应起到了有效的催化作用,且计算所得结论与实验结果相符合.     

甲醇分子(CH3OH)光谱性质的理论计算

研究了气相甲醇分子(CH3OH)基态和激发态性质。在对不同方法基组所得计算结果和实验结果进行比较之后,选用MP2(full)/6-311++G(2d,2p)理论方法进行计算,得到甲醇分子(CH3OH)基态和三重激发态的几何结构、能量以及频率信息;频率计算显示基态和三重态都为稳定构型。从三重态的结构出发,解释了三重态势能面为排斥型势能面的合理性。计算了甲醇分子单重激发态的垂直激发能,比较不同方法不同基组计算的甲醇分子单重激发态的垂直激发能,发现用TDDFT 中的b3p86方法使用6-311++G**基组的计算值和实验值符合得最好。计算得到的甲醇分子在MP2(full)/6-311++G(2d,2p)的绝热电离能和垂直电离能分别为11.18eV和11.32eV;计算得到的绝热电子亲和势与垂直电子亲和势分别为0.888eV和0.893eV。计算结果对实验研究有指导意义。     

甲醇分子(CH3OH)光谱性质的理论计算

研究了气相甲醇分子(CH3OH)基态和激发态性质。在对不同方法基组所得计算结果和实验结果进行比较之后,选用MP2(full)/6-311++G(2d,2p)理论方法进行计算,得到甲醇分子(CH3OH)基态和三重激发态的几何结构、能量以及频率信息;频率计算显示基态和三重态都为稳定构型。从三重态的结构出发,解释了三重态势能面为排斥型势能面的合理性。计算了甲醇分子单重激发态的垂直激发能,比较不同方法不同基组计算的甲醇分子单重激发态的垂直激发能,发现用TDDFT 中的b3p86方法使用6-311++G**基组的计算值和实验值符合得最好。计算得到的甲醇分子在MP2(full)/6-311++G(2d,2p)的绝热电离能和垂直电离能分别为11.18eV和11.32eV;计算得到的绝热电子亲和势与垂直电子亲和势分别为0.888eV和0.893eV。计算结果对实验研究有指导意义。     

Rh的芳基化合物与含氮芳基卤代物交叉偶联反应机理研究

利用密度泛函理论(DFT)研究了Rh的芳基化合物与含氮芳基卤代物交叉偶联过程催化循环的微观反应机理.在B3LYP/6-31+G(d)基组水平上(Rh、I采用了赝势基组Lan L2DZ)优化了反应过程中所有化合物的几何构型并计算了频率,通过能量、频率和振动方式确定了中间体和过渡态的真实性.此外,在同等基组水平上还运用了分子中的原子理论讨论了成键临界点的电荷密度的变化,运用了自然键轨道理论讨论了键的性质与轨道间的相互作用.为了提高计算精度,在6-311++G(d,p)基组水平上计算了反应机理中所有物质在气相及溶剂化下的单点能,得到与6-31+G(d)基组计算相同的结论 .结论表明Rh(Ⅰ)起到了有效的催化作用,且计算所得结论与实验结果相符合.     

Push–pull hyperbranched molecules. A theoretical study

The electronic properties of the ground state, unrelaxed and relaxed first excited states of push–pull hyperbranched molecules bearing amino and nitro terminal groups have been studied at BB1K/cc‐pvdz//HF/6‐31g(d), TD‐BB1K/cc‐pvdz//HF/6‐31g(d) and TD‐BB1K/cc‐pvdz//CIS/6‐31g(d) levels of theory, respectively. It was demonstrated that dendritic architecture of push–pull molecules favours the charge transfer in the excited state compared to linear molecules. The possibility of adopting a plane conformation is an important condition for the charge transfer in an excited state. According to the calculations 1:1 ratio of donor and acceptor groups is another important precondition for the manifestation of strong charge separation in the excited state. In case of excess of nitro groups over the amino, some of the excitations participating in the S0 → S1 transition favour the charge transfer in the excited state in the opposite directions, thus decreasing the charge separation. Copyright © 2008 John Wiley & Sons, Ltd.     

Excitation Wavelength Dependence of Dual Fluorescence of DMABN in Polar Solvents

Steady-state absorption, fluorescence excitation and emission spectra of 4-(N,N-dimethylamino)benzonitrile (DMABN) have been measured at room temperature in cyclohexane, 1,4-dioxane, dichloromethane, and acetonitrile solutions. The fluorescence spectra of DMABN are found to exhibit dual emission in 1,4-dioxane, dichloromethane, and acetonitrile solutions and single emission in cyclohexane solution. The effect of solvent polarity and excitation wavelength on the emission spectra has also been studied. The fluorescence excitation spectra of DMABN monitored at the emission bands are different. The presence of two different conformations of the same molecule in the ground state has lead to two close lying excited states; local excited (LE) and charge transfer (CT), and thereby results in the dual fluorescence of the compound. The experimental studies were supported by ab initio density functional theory (DFT) calculations performed at the B3LYP/6-31Gd level of theory. On the basis of the experimental results and our theoretical calculations, we suggest that there are two conformers of DMABN, which are stable in the ground state, equilibrated in solution at room temperature that give rise dual fluorescence upon excitation.     

An investigation of the structure of free-base porphycene by time-resolved electron nuclear double resonance and density functional theory on the photoexcited triplet state

The photoexcited triplet state of free-base porphycene has been investigated by time-resolved electron nuclear double resonance spectroscopy at 10 K. In order to determine whether porphycene is cis or trans configured, experimentally determined A_zz hyperfine coupling tensor components are compared with those predicted from density functional theory. The structures of cis and trans porphycene, in both the singlet ground state and lowest excited triplet state were calculated using the Becke3-Lee-Yang-Parr composite exchange correlation functional and the 6–31G* basis set. Hyperfine couplings for these structures were then calculated using the same functional but with the extended EPR-II basis set. From the results it can be concluded that porphycene has a trans configuration in both the ground singlet and lowest excited triplet state. Additionally, the significant differences in structure between the singlet and triplet states are reflected in the calculated hyperfine couplings, with those for the trans conformation in the triplet state in reasonable agreement with the experimental values.     

Theoretical model of triplet-triplet annihilation

The electronic mechanism of triplet-triplet annihilation resulting in the delayed fluorescence of organic molecules in liquid solutions is investigated. There is a discussion of the nature and strength of the interactions which lead to radiationless energy transfer between two triplet-excited molecules in a collision complex, when the first excited singlet state of one of the molecules is filled. The role of intermediate states with charge transfer and also of the unstable excimer state in the contact complex is noted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 12–17, September, 1978.     

Photoinduced energy and electron transfer in oligo(<Emphasis Type="Italic">p</Emphasis>-phenylene vinylene)-fullerene dyads

The intramolecular photoinduced charge separation within an oligo(p-phenylene vinylene)–fulleropyrrolidine dyad with four phenyl rings (OPV4-C₆₀) has been investigated with femtosecond pump-probe spectroscopy in solvents of different polarity and in the solid state. In solution, photoexcitation of the OPV4 moiety of OPV4-C₆₀ results in an ultrafast (<190 fs) singlet energy transfer reaction, creating the fullerene singlet excited state. In polar solvents, the ultrafast energy transfer is followed in the picosecond time domain by an intramolecular electron transfer. In accordance with Marcus theory, the rates for forward and backward intramolecular electron transfer in OPV4-C₆₀ are influenced by the polarity of the solvent. In the solid state the photophysics of OPV4-C₆₀ is dramatically different. In thin films, the forward electron transfer proceeds within 500 fs, irrespective of which chromophore is photoexcited. The increased rate for charge separation in the solid state is attributed to a more favorable orientation of the donor and acceptor that results in an intermolecular electron transfer. In the films, energy and electron transfer processes compete at the earliest moments after photoexcitation. In the solid state, the photogenerated electrons and holes have long lifetimes as a result of migration of these charges to thermodynamically more favorable sites in the film. PACS 78.47.1+p; 34.30.+h; 33.50.-j     

外电场下TCNQ的激发与光谱性质研究

采用密度泛函B3PLY方法优化了不同外电场下TCNQ分子的基态稳定构型、电偶极矩和分子的总能量,并且分析了TCNQ分子的HOMO-2到LUMO+2轨道的能量变化。然后利用杂化CIS-DFT方法在同样的基组下计算了外电场下TCNQ分子的前9个激发态的激发能、波长和振子强度,结果表明在没有外电场的情况下,TCNQ分子只有一个激发态能够激发,从基态跃迁到第1激发态。在有外电场的作用下,总能量随外电场的增加而逐渐减少,偶极矩随外电场的增加而不断增加。其前线轨道的能量也随外电场的增加不断减少,轨道分布也受外电场很大的影响。另外,外电场对TCNQ分子的激发波长也产生了一定影响。     

外电场下TCNQ的激发与光谱性质研究

采用密度泛函B3PLY方法优化了不同外电场下TCNQ分子的基态稳定构型、电偶极矩和分子的总能量，并且分析了TCNQ分子的HOMO-2到LUMO+2轨道的能量变化。然后利用杂化CIS-DFT方法在同样的基组下计算了外电场下TCNQ分子的前9个激发态的激发能、波长和振子强度，结果表明在没有外电场的情况下，TCNQ分子只有一个激发态能够激发，从基态跃迁到第1激发态。在有外电场的作用下，总能量随外电场的增加而逐渐减少，偶极矩随外电场的增加而不断增加。其前线轨道的能量也随外电场的增加不断减少，轨道分布也受外电场很大的影响。另外，外电场对TCNQ分子的激发波长也产生了一定影响。     

Photoinduced Intramolecular Electron Transfer and Electronic Coupling Interactions in π- Expanded Imidazole Derivatives

An intramolecular excited charge transfer (CT) analysis of imidazole derivatives has been made. The determined electronic transition dipole moments has been used to estimate the electronic coupling interactions between the excited charge transfer singlet state (¹CT) and the ground state (S₀) or the locally excited state (¹LE). The properties of excited ¹CT state imidazole derivatives have been exploited by the significant contribution of the electronic coupling interactions. The excited state intramolecular proton transfer (ESIPT) analysis has also been discussed.     

Steady state and time-resolved spectroscopic investigations on the photoreactions involved within the electronically excited electron acceptor 9-cyanoanthracene in presence of benzotriazole and benzimidazole donors

The electrochemical, “steady-state” and “time-resolved” spectroscopic investigations were made on the well-known electron acceptor 9-cyanoanthracene (CNA) when interacted with the electron donors benzotriazole (BZT) and benzimidazole (BMI) molecules. Though electrochemical measurements indicate the thermodynamical possibility of occurrences of photoinduced electron transfer reactions within these reacting systems in the lowest excited singlet state (S₁) of the acceptor CNA but the steady-state and time-resolved measurements clearly demonstrate only the triplet-initiated charge separation reactions. It was reported earlier that in the cases of disubstituted indole molecules the occurrences of photoinduced electron transfer reactions were apparent both in the excited singlet and triplet states of the acceptor 9-cyanoanthracene, but the similarly structured present donor molecules benzotriazole (and benzimidazole) behave differently from indoles. The weak ground state complex formations within the presently studied reacting systems appear to be responsible for the observed static quenching phenomena as evidenced from the time-resolved fluorescence studies. Time-resolved spectroscopic investigations demonstrate the formation of the ground state of the reacting components (donor and acceptor) through recombination of triplet ion-pairs via formations of contact neutral radical produced by H-abstraction mechanism.