光致电子转移对Rhodamine 6G基态分子结构影响的非共振Raman光谱研究

基于非共振Raman 光谱和量子化学计算, 研究了在纯电子给体N,N-二乙基苯胺(DEA)溶剂中Rhodamine 6G (Rh6G⁺)基态分子结构的变化, 这有利于理解该体系中的光致分子间电子转移(PIET). 与PIET相耦合的所有振动模式已被确定和指认. 结果表明: 对应于氧杂蒽环且位于675 cm^-1处最主要的振动模式对PIET 有着至关重要的贡献; 通过与电荷转移复合物(Rh6G/DEA⁺)的发色团芳香族环的C―C伸展振动模式作比较, C=C伸展振动对PIET的影响更敏感. 本文的研究工作能为具有合适电子转移特性的光伏器件中分子结构或溶剂环境的设计提供新颖的观点.     

N-甲基吡咯-2-甲醛激发态结构动力学及其溶剂效应的共振拉曼光谱和密度泛函理论研究

获取了覆盖N-甲基吡咯-2-甲醛(NMPCA)A-带和B-带电子吸收共7个激发波长的共振拉曼光谱,并结合含时密度泛函理论(TD-DFT)方法研究了的A-带和B-带电子激发和Franck-Condon区域结构动力学.TD-B3LYP/6-311++G(d,p)计算表明:A-带和B-带电子吸收的跃迁主体为π→π*.共振拉曼光谱可以指认为,11-13振动模式(A-带激发)或者7-11振动模式(B-带激发)的基频、倍频和组合频,其中C=O伸缩振动(ν7)、环的变形振动+N1-C6伸缩振动(ν17)、环的变形振动(ν21)和C6-N1-C2/C2-C3-C4不对称伸缩振动(ν14)占据了绝大部分.这表明NMPCA的Sπ激发态结构动力学主要沿C=O伸缩振动、环的变形振动和环上N1-C6伸缩振动等反应坐标展开.在同一溶剂的共振拉曼光谱中随激发波长由长变短,ν7与ν14的强度比呈现出由强变弱再变强的现象,这种变化规律被认为与Franck-Condon区域Sn/Sπ态混合或势能面交叉有关.溶剂对Sn/Sπ态混合或势能面交叉具有调控作用.     

2-乙酰基-1-甲基吡咯激发态结构动力学及溶剂效应的共振拉曼光谱和密度泛函理论计算

获取了覆盖紫外光谱中A带和B带吸收的共7个不同激发波长的共振拉曼光谱, 并结合密度泛函理论方法研究了2-乙酰基-1-甲基吡咯(2-Ac-NMP)的A带和B带电子激发和Franck-Condon区域结构动力学. 在TD-B3LYP/6-311++G(d,p)计算水平上, A带和B带吸收的跃迁主体为π→π^* . A带和B带共振拉曼光谱分别指认为13个振动模式和8个振动模式的基频、泛频和组合频, 其中C＝O伸缩振动(ν₈)、C3-C4-C5不对称伸缩振动+C2-C6伸缩振动(ν₁₄)及环上CH面内摇摆(ν₁₈)对拉曼光谱强度贡献最大, 表明2-Ac-NMP的S_π激发态结构动力学主要沿反应坐标展开. 考察了溶剂对共振拉曼光谱强度模式的影响, 结果表明, 在同一溶剂中, 随激发波长由长变短, C＝O伸缩振动模(ν₈)的强度呈现出由强变弱再变强的现象. 这种变化规律与Franck-Condon区域S_n/S_π态混合或势能面交叉相关, 并受溶剂的有效调控.     

Rh6G-DMTC分子间能量转移的荧光光谱研究

利用N_2激光器作为激发光源, 测量若丹明6G(Rh6G)和N,N′-二甲基噻碳菁碘盐(DMTC)不同浓度混合的乙醇溶液的荧光光谱, 证明 Rh6G-DMTC组成施主-受主对, 存在着分子间能量转移效应。通过对DMTC荧光强度与Rh6G浓度的关系的测量, 讨论了Rh6G-DMTC能量转移的机制, 并且导出了辐射转移和Förster转移两种典型过程中受主荧光强度与施主浓度的关系式。     

锗苯与腈氧化物1,3偶极环加成反应理论研究

采用密度泛函理论(DFT)方法在B3LYP/6-311G**水平研究了锗苯与腈氧化物的1,3偶极环加成反应的微观机理、势能剖面,考察取代基和四氢呋喃溶剂对反应势能剖面的影响.计算结果表明,所研究反应均以协同但非同步的方式进行,且总是Ge—O键先于C—C键形成.锗苯分子中Ge原子上的给电子和吸电子取代基均有利于反应的进行,而腈氧化物C原子上的2,4,6-三甲苯基取代基在热力学上对反应很不利.四氢呋喃溶剂对所研究反应的势能剖面影响不大.     

新颖的5,15-二(4-(5-乙酰基硫戊氧基)苯基)卟啉化合物的结构和性质的密度泛函理论计算

通过密度泛函理论计算比较性地研究了5,15-二(4-(5-乙酰基硫戊氧基)苯基)自由卟啉及其锌配合物的分子结构、电荷性质、分子轨道、电子吸收光谱和红外光谱.这类化合物具有在卟啉相对的两个中位的苯环上连有5-乙酰基硫戊氧基的新颖结构.模拟得到的这两个化合物的分子结构和电子吸收光谱以及红外光谱都与实验测得的符合得很好.通过与未取代的自由卟啉和卟啉锌的结构和性质进行比较,研究了中位取代基、极性溶剂和中心金属取代对此类卟啉化合物结构和性质的影响规律.对化合物的电子吸收光谱中的电子跃迁本质进行了归属,并通过基于正则坐标分析产生的动画对红外光谱的振动模式进行了指认.目前的工作将对理解此类新颖卟啉化合物的结构和性质以及取代基和溶剂效应提供很大的帮助.     

N-(ω-三丁基锡)烷基邻苯二甲酰亚胺的光诱导环化反应

N-(ω-三丁基锡)烷基邻苯二甲酰亚胺在光诱导下生成环化物.在强亲核性溶剂中反应以单电子转移机制进行,并以很高的产率得到环化物;在弱亲核性溶剂中Norrish Type Ⅱ和单电子转移机制同时存在.     

尿嘧啶和5-氯尿嘧啶1S0→1S2跃迁动态结构的共振拉曼光谱

采用含时量子波包理论的简单模型对5-氯尿嘧啶和尿嘧啶的共振拉曼光谱开展了强度分析拟合, 获得了1(π, π*)激发态的几何结构变化动态特征. 结果表明, 尿嘧啶1S0→1S2跃迁的动态结构特征因5-位氯原子取代而改变. 5-氯尿嘧啶的动态结构特征主要沿C5=C6伸缩振动+C6H12 弯曲振动和N3H9/N1H7弯曲振动+N1C6伸缩振动反应坐标展开, 而尿嘧啶的动态结构特征主要沿嘧啶环的伸缩振动+C5H11/C6H12/N1H7弯曲振动和C4=O10伸缩振动反应坐标展开. π和π*轨道中氯原子的pz电子参与嘧啶环的p-π共轭作用导致了在1(π, π*)激发态上5-氯尿嘧啶的振动重组能更多地配分给嘧啶环的弯曲振动模式和C5=C6伸缩振动模式. 尿嘧啶在甲醇中的激发态动态结构特征与在水中的基本一致, 但波包沿C5H11/C6H12/N1H7弯曲振动+N1C6伸缩振动(υ12)和环呼吸振动(υ17)反应坐标的运动明显增强.     

甲氧基在Rh(111)表面吸附的密度泛函研究

采用密度泛函理论(DFT)的B3LYP方法,以原子簇Rh13(9,4)为模拟表面,在6-31G(d,p)与Lanl2dz基组水平上,对甲氧基在Rh(111)表面的四种吸附位置(fcc、hcp、top、bridge)的吸附模型进行了几何优化、能量计算、Mulliken电荷布局分析以及前线轨道的计算。结果表明,当甲氧基通过氧与金属表面相互作用时,在bridge位的吸附能最大,吸附体系最稳定,在top位转移的电子数最多;吸附于Rh(111)面的过程中C—O键被活化,C—O键的振动频率发生红移。     

二氢硫辛酸抗氧化性机理的理论研究

分别在B3LYP/6-31G(d,p)和B3LYP/6-311++G(d,p)水平下,对二氢硫辛酸及可能的解离途径中形成的自由基进行结构优化,采用S—H键解离焓(EBD)和分子的电离势(EIP)为理论指标,探讨了二氢硫辛酸可能的抗氧化性机理,并研究了溶剂(水和苯)效应的影响.结果表明,C(1)上S—H断裂形成的自由基b较易形成;以EBD和EIP为理论指标,可以较好的说明分子的抗氧化性及溶剂效应对抗氧化性的影响.随着溶剂的极性增加,EBD变化较小,而EIP则显著减小,表明溶剂效应对清除自由基的电子转移反应机理影响更大.分子最高占据轨道HOMO能级顺序与EIP数值所预测的抗氧化性顺序一致.     

O2+O2 electron transfer reactivity in the quartet state from ab initio calculation including electron correlation

The structures and properties of the O₂+O₂⁻ electron transfer system in the quartet state, both in the gaseous phase and in solution, were studied at the UMP2(full)/6-311+G* basis set level for the five selected coupling structures: two T-type, collinear, parallel, and crossing. The stabilities of these encounter complexes were compared. The activation barriers, coupling matrix elements, and the electron transfer rate at two theoretical levels (semiclassical and quantum mechanical) were also calculated for the quartet state, and the effect of the solvent medium evaluated at the self-consistent reaction field level. Results indicate that the structures and properties of the encounter complexes directly affect the mechanism and rate of the electron transfer reaction, the contact distances for this O₂…O₂⁻ were generally large (3 Å), the interaction between the donor and the acceptor was weak, and the structures are floppy. The electronic transmission factor for the reacting system, O₂+O₂⁻, was less than unity (ca. 001–0.6), thus the electron transfer reaction was non-adiabatic in nature. Analysis of the dependence of relevant kinetic parameters on various influencing factors showed that the effect of the solvent medium on the coupling matrix element was small, but that on the electron transfer rate was very large, and the gaseous phase results for the molecular geometrical parameters and their contributions can directly transfer to solution. Among the five selected transition state structures, the electron transfer was more likely to take place via the T-type and the P-type structures, the rate values from two theoretical levels were in good agreement with each other and were also very close to the experimental findings. If the various anharmonic vibrational contributions, the effect of the solvent molecular electronic structures and the interaction between the reacting species and the solvent medium are taken into account, the results can be improved.     

Photo-Induced Intermolecular Electron Transfer-Effect of Acceptor Molecular Structures

Photo-induced electron transfer versus molecular structure of acceptors is investigated using ultrafast time-resolved transient grating spectroscopy. Typical laser dyes Rhodamine 101 (Rh101) and Rhodamine 6G (Rh6G) in electron donor solvent-aniline are adopted as the objects. The forward electron transfer time constant from aniline to the excited singlet state of two Rhodamine dyes and subsequent back electron transfer from two dyes to aniline are measured. The experimental results denote that Rh6G presents faster electron transfer rates with aniline in both forward electron transfer and back electron transfer processes. With chemical calculation and qualitative analysis, it is found that the flexible molecular geometry of Rh6G leads to stronger electron coupling with donor solvent and further gives rise to larger electron transfer rates.     

Ab initio study on the structures, energies, and vibrational frequencies of acetone complexes with metal monocations and dications

The structures, interaction energies, and vibrational frequencies of acetone and its complexes with proton and various metal monocations/dications such as H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Be²⁺, Mg²⁺, Ca²⁺, and Zn²⁺ have been investigated from the ab initio calculations. The linear or bent structure for the cation-acetone complexes has been found to be deeply influenced by the amount of charge transfer. The amount of red-shift of CO stretching frequencies of acetone is almost equivalent regardless of the kind of alkali metal monocations. This behavior can be attributed to the electrostatic nature of the interactions rather than orbital interactions. This phenomenon has been supported by the highest occupied molecular orbitals of the acetone complexes investigated, charge transfer based on natural bond orbital (NBO) atomic charges, and the inversely proportional behavior of the interaction energies to the interatomic distances r(M⁺O).     

脯氨酸与Cu、Cu~+和Cu~(2+)配位体系的计算研究

运用M06-2X和ωB97XD方法分别在6-311++G(2d,p)和TZVP基组水平上,对脯氨酸(Pro)的15种构象与Cu、Cu+和Cu2+形成的多种配合物的几何结构、能量学特征、振动光谱和电子结构等进行计算研究.四种水平得到20种[Pro-Cu]、16种[Pro-Cu]+和16种[Pro-Cu]2+稳定结构.[Pro-Cu]和[Pro-Cu]+体系中出现12种Pro构象,而[Pro-Cu]2+体系中出现11种Pro构象,三种体系中最稳定的结构都不是由能量最低的Pro构象生成的.在结构CI3、CI4、CII7和CII8中,Pro的羧基氢转移到亚氨基氮形成两性离子与Cu双配位结合.[Pro-Cu]0/1+/2+体系四种水平计算相对能差范围逐渐增加,结合能分别在-60.0--5.0 kJ·mol-1、-340.0--170.0 kJ·mol-1和-1100.0--860.0 kJ·mol-1范围,配位体系中Pro的变形能逐渐增加.N―H和O―H键伸缩振动频率普遍发生红移,配位体系中部分电荷从Pro转移到Cu上,在[Pro-Cu]2+体系中单配位结构中电荷转移最多,约为单位负电荷.     

Effect of the nature of mendiaxon–X interactions (X= Na, Cu, H) and the hydrogen bonding on the ν(C=O) behavior: theoretical and spectroscopic study

Theoretical and spectroscopic (IR and Raman) study of different 7-hydroxy-4-methylcoumarin (mendiaxon) systems (mend⁻, mendNa, mendCu, mendH and mendH · 2H₂O) were performed at B3LYP/6-31G(d) and B3LYP/6-31++G(d,p) levels of theory. The geometric and electronic structures as well as the vibrational behavior of the systems studied were discussed: (1) as to the changes that occurred in the anion coumarin ring upon the mend⁻–X⁺ (X⁺ =Na⁺, Cu⁺, H⁺) interactions and (2) as to the changes that occurred in mendH due to hydrogen bondings in mendH · 2H₂O. The largest bond length changes in the anion coumarin ring were obtained for mendH and the smallest ones for mendNa. The bond length changes were mainly produced from the electrostatic effect of the positive charge of X. The induced polarization of the C=O bond upon the mend⁻–X⁺ interactions was found to be opposite to the basic one and it led to shorter C=O bond lengths (higher ν(C=O) frequencies) in the order: mendNa, mendCu and mendH. Conversely, upon the hydrogen bonding the induced polarization of the C=O bond was found in the same direction as the basic one and it produced elongation to the C=O bond length (lower ν(C=O) frequency). On the basis of the correlations found, the ν(C=O) positions in mendNa, mendCu, mendH and mendH · 2H₂O were explained.     

Vibrational dependence of the NH3 (v2)+NO and NO(v)+NH3 charge transfer cross sections

A tandem quadrupole mass spectrometer is used to study the charge transfer reactions NH₃⁺ + NO and NO⁺ + NH₃ over a collision energy range 1.5–13 eV. The vibrational state of the reagent ions is selected by resonance-enhanced multiphoton ionization. For the 0.9 eV exothermic process NH₃⁺ + NO → NH₃ + NO⁺ excitation of the v₂ umbrella bending mode (v₂ = 0–12) causes no marked change in the charge transfer cross section, while in the reverse process NO⁺ + NH₃ → NO + NH₃⁺ excitation of the NO⁺ vibration (v = 0–6) strongly enhanced the charge transfer cross section.     

异丙醇的O-H伸缩振动泛频光谱和分子构像

使用高灵敏的光腔衰荡光谱(CavityRingDownSpectroscopy)技术测出了异丙醇的O-H伸缩v=4、5振动泛频光谱,每个振动能级都有三个吸收峰,被归属为分子构像的O-H伸缩泛频吸收.给出了光腔衰荡光谱的振动泛频吸收的谱带强度公式,并求得分子不同构像在不同振动能级的O-H伸缩泛频吸收的谱带强度;同时利用局域模理论,求得分子各O-H伸缩局域模振子的机械频率(X1)、非谐性(X2)以及解离能(D).用密度泛函(DFT)B3LYP/6-31+G*理论方法优化了分子的各种可能构像,验证了分子存在反式(trans)和偏转(gauche)两种稳定构像,计算的分子的O-H伸缩频率及构像稳定性同实验结果是一致的.     

气相中CrO2+和H2反应的理论研究

用密度泛函UB3LYP/6-311++G(3df, 3pdpd)//6-311G(2dd, p)方法计算研究了在二重态和四重态两个势能面上的气相反应：CrO₂⁺ + H₂→CrO⁺+ H₂O. 对影响反应机理和反应速率的势能面交叉进行了讨论, 并运用Hammond 假设和Yoshizawa 等的内禀反应坐标(IRC)单点垂直激发计算的方法找出了势能面交叉点(crossing point (CP)). 运用碎片分子轨道(fragment molecular orbital(FMO))理论, 对初始复合物2IM1和4IM1的轨道相关进行了分析, 解释了CrO₂⁺活化H—H σ键及H₂迁移的机理.     

黄曲霉素B_2分子吸附在银团簇的表面增强拉曼散射机理

采用密度泛函理论(DFT)B3LYP方法,6-311G(d,p)(C,H,O)/LANL2DZ(Ag)基组,计算了黄曲霉素B2(AFB2)分子吸附在Ag2团簇的表面增强拉曼散射(SERS)光谱和预共振拉曼光谱,并与实验结果比较.结果显示:AFB2分子在基态Ag2团簇表面吸附时,增强因子最大达到102,对应吡喃(pyrane)环C=O伸缩振动,主要是由AFB2分子周围化学环境改变而引起的基态静极化率改变导致的化学增强.不同激发波长下的AFB2分子预共振拉曼光谱的增强强度不同:电荷转移态激发波长为1144和544 nm时拉曼信号增强了102倍,而选择电荷转移预共振波长432和410 nm作为入射光时,其拉曼信号增强了104倍,增强机理为银团簇和黄曲霉素分子之间的电荷转移共振增强.因此通过改变入射光波长,选择电荷转移共振激发波长,更有利于强致癌物AFB2分子的痕量检测.