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(英文)

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.     

1-甲基胸腺嘧啶A-带结构动力学

获取了1-甲基胸腺嘧啶(MT)涵盖紫外光谱中A带和B带吸收的共5 个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MT的电子激发和Franck-Condon 区域结构动力学. 在TD-B3LYP/6-311++G(d,p)计算水平下, A带和B带吸收被分别指认为π_H→π_L^*/π_H-2→π_L+2^*和π_H→π_L+2^→/π_H-2→π_L^*跃迁. 甲基参与嘧啶环的共轭使MT的A带最大吸收波长λ_max相对于胸腺嘧啶(T)发生明显红移, 并对Franck-Condon区域的动态结构产生一定影响. A带和B带共振拉曼光谱分别被指认为14 个振动模式和11 个振动模式的基频、泛频和组合频. C5＝C6伸缩+C6H12面内弯曲振动v₉, 环变形振动v₁₆和N3C2N1反对称伸缩+C4C5C10反对称伸缩振动v₁₈占据了A带共振拉曼光谱强度的绝大部分. 这表明¹π_Hπ_L^*激发态结构动力学主要沿这些反应坐标展开. 考察了溶剂对共振拉曼光谱的影响, 结果表明, C4＝O9伸缩+N3H11面内弯曲振动v₈的活性与溶剂性质有关, 其激发态位移量随溶剂性质的变化规律与胸腺嘧啶一致.     

铜转运蛋白C端金属结合域与Ag+及Hg2+的相互作用

铜转运蛋白(CTR1)不仅参与铜的细胞摄取,而且在其它重金属离子的摄取过程中也发挥重要作用. 本文采用紫外-可见(UV-Vis)光谱,核磁共振(NMR)和质谱(MS)的方法,研究了人源CTR1 (hCTR1)的C端金属结合域(C8)与Ag⁺和Hg²⁺的相互作用. 研究表明,Ag⁺和Hg²⁺都能与C8结合,但二者与C8的结合机制明显不同. 每个C8分子可以结合两个Ag⁺离子,但一个Hg²⁺却可以与两个C8形成桥联. 此外,Ag⁺离子与C8的配位是一个中等速度的交换过程,而Hg²⁺离子则为快速交换过程. C8的半胱氨酸残基是两种离子的重要结合位点,同时组氨酸残基也参与两种金属离子的配位,其中Ag⁺优先结合组氨酸,而Hg²⁺则对半胱氨酸的结合具有显著的优势. 虽然HCH基序对C8 与金属配位至关重要,一些远端的其它氨基酸也可以参与C8 与银离子的配位,这可能与CTR1 在摄取Ag⁺过程中的金属转移机制相关. 这些结果为理解hCTR1 蛋白摄取重金属离子的作用机制提供了必要的信息.     

糠醛在Pt(111)表面的吸附和脱碳反应

采用广义梯度近似的密度泛函理论并结合平板模型的方法, 优化了糠醛分子在Pt(111)面的吸附模型,并探究了糠醛脱碳反应形成呋喃的机理. 结果表明: 吸附后糠醛分子环上的C―H(O)键及支链―CHO相对于金属表面倾斜上翘, 分子平面被扭曲, 易于呋喃的形成; 同时, 糠醛分子向Pt表面转移电子0.765e, 环中的大π键与Pt(111)表面的d轨道发生较强的相互作用, 使得糠醛的芳香性被破坏, 环上的碳原子呈现准sp³杂化. 此外, 对糠醛脱碳反应中的各反应步骤进行过渡态搜索, 通过比较各步骤的活化能, 得出糠醛更易先失去支链上的H形成酰基中间体(C₄H₃O)CO, 中间体继续脱碳加氢形成产物呋喃. 该过程的控速步骤为(C₄H₃O)CO^*+^*→C₄H₃O^*+CO^* (^*为吸附位),活化能为127.65 kJ·mol^-1.     

YS+(1Σ+, 3Φ)与COS气相反应: YS++COS→YS2++CO的理论研究

采用密度泛函B3LYP方法研究了硫化钇离子YS⁺ (¹Σ⁺, ³Φ)与硫转移试剂COS在气相中的反应: YS⁺+COS→YS₂⁺+CO. 在单重基态和三重激发态势能面上都找到了四条反应通道. 但是除一条反应通道之外, 其他的反应机理和几何结构变化趋势在不同的势能面上有很大不同. 实验中生成YS₂⁺ 所表现出的吸热特征来自于在基态反应中的三条通道(A, B和C), 其活化势垒分别为28.3, 140.5和120.2 kJ·mol^-1. 计算结果表明硫转移反应没有双态反应活性, 因此产物YS₂⁺ 在低能量区的放热特征是由于基态反应物中还混有残留的激发态YS⁺.     

气相中Sc+和Ti+与CS2反应的计算研究

以Sc⁺和Ti⁺与CS₂反应作为第一前过渡金属离子与CS₂反应的范例体系. 采用密度泛函(UB3LYP/6-311+G*)方法计算研究了Sc⁺和Ti⁺在基态和激发态与CS₂反应的反应机理. 全参数优化了反应势能面上各驻点的几何构型, 用频率分析方法和内禀反应坐标(IRC)方法对过渡态进行了验证. 计算了不同多重度下的反应交叉势能面. 确定了Sc⁺和Ti⁺与CS₂的反应为插入-消去反应, 找到了基态和激发态金属离子与CS₂反应的主要通道.     

含轴向咪唑配体的手性SalenCo(III)配合物ECD谱的理论解析

用密度泛函理论(DFT)方法, 在B3LYP和混合基组(C, H原子用6-31G^*; Co, N, O用6-311+G(2d,p))水平上, 对含轴向配体的三种Co(III)席夫碱配合物[Co(MeO-salen)(Im)₂]⁺、[Co(MeO-salen)(2-MeIm)₂]⁺和[Co(MeO-salen)(MeIm)₂]⁺ (Im=咪唑, MeIm=1-甲基咪唑, 2-MeIm=2-甲基咪唑, MeO-salenH₂=salen型席夫碱, 即(R,R)-N,N′-双(5-甲氧基亚水杨基)-1,2-二亚胺基环己烷)在二氯甲烷溶液中的基态结构进行了优化, 并用含时密度泛函理论(TDDFT)方法, 在相同泛函和基组水平上计算了其激发能、振子强度和旋转强度. 这些计算中均用极化连续介质模型(PCM)考虑了溶剂效应. 计算的电子圆二色(ECD)谱与实验谱吻合较好. 通过对有关跃迁性质的分析, 对实验电子圆二色光谱进行了解析与指认. 结果表明, 长波区的第一个圆二色(CD)吸收带主要是由π→d荷移跃迁(LMCT)引起的, 而不是通常认为的d→d跃迁. 轴向配体的加入对配合物前两个CD吸收带的符号没有影响, 但会影响带形和强度. 手性salen配合物的绝对构型为λ(RR)时, 第一个CD吸收带为正, 第二个为负. 这些结论对于深入理解该类配合物的电子结构和手征光学性质具有重要的科学意义.     

单电子卤键复合体系H3C···Br-Y(Y=H, CN, NC, CCH, C2H3)的作用机制

对单电子溴键复合物H₃C···Br—Y(Y=H, CCH, CN, NC, C2H3)的结构与性质进行了理论研究. 在B3LYP/6-311++G**水平上计算了稳定构型并做了频率分析. BSSE矫正的相互作用能(E^BSSE)和NBO及AIM分析输入的波函数在MP2/6-311++G**水平下完成. 复合物H₃C···Br—Y中, CH₃(供电子体)自由基均提供一未成对电子与Br—Y中Br(受电子体)形成了单电子溴键, 此单电子溴键也具有“三电子”键的特征. 单电子溴键的形成导致甲基H的背向Y弯曲和Br—Y键的拉长及红移单电子溴键复合物的产生. 考察了电子受体中不同取代基, C(spⁿ)-Br杂化及溶剂的存在对复合物作用的影响, 将单电子氢键, 单电子卤键和单电子锂键的作用强度做了对比, 进一步对Popelier提出的氢键体系中的前三个重要拓扑指标在单电子溴键体系中的重现性进行了探讨.     

π堆积的腺嘌呤-胸腺嘧啶体系激发态电荷转移和无辐射失活的半经典动力学模拟

采用半经典电子-辐射-离子动力学(SERID)模型模拟了π堆积的腺嘌呤-胸腺嘧啶(A-T)体系激发态的光物理失活过程. 设置激光脉冲仅作用于T, 模拟发现电子由A转移到T, 形成(A⁺T^-)^*激基缔合物(exciplex). 当分子间距缩短至0.300 nm时, 由于轨道离域效应产生电荷重组, 体系恢复电中性; 当A分子的C4'－C5'扭曲程度最大时, 体系通过避免交叉点衰减至基态. Exciplex 的失活途径由分子间距离和A分子的变形程序两个因素决定. 由于A分子的C4'、C5'原子位阻较大, 难以达到失活所必需的强烈扭曲, 因此(A-T)^*的寿命比胸腺嘧啶堆积体系(T-T)^*显著增长.     

N-烷基吡啶阳离子及其与若干阴离子形成的离子对结构的理论研究

采用密度泛函理论方法, 在B3LYP/6-31＋G(d) 水平上研究了吡啶、N-烷基吡啶阳离子及其与若干阴离子(F^－, Cl^－, Br^－, , )形成的离子对的稳定构型. 计算结果表明: N-烷基吡啶阳离子的吡啶环与中性吡啶分子类似, 具有芳香性, 烷基对吡啶环结构影响不大; 离子对中阴离子易出现在吡啶环上方以及C(5)—H 或C(2)—H 和 N-甲基附近; 阴、阳离子之间通常存在多重氢键, 并且均有部分电荷转移; 离子对的相互作用能随着N-烷基的增长而减小.     

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.     

Structural and vibrational studies of molecular conductors using quantum mechanical methods: 1,3-Dithiole-2-thione, 1,3-dithiole-2-one, 1,3-dioxole-2-one and 1,3-dioxole-2-thione

Computations were carried out by employing the RHF and density functional theory (DFT) methods to investigate the geometries, atomic charges, harmonic vibrational frequencies for the 1,3-dithiole-2-thione (DTT), 1,3-dithiole-2-one (DTO), 1,3-dioxole-2-thione (DOT) and 1,3-dioxole-2-one (DOO) molecules and their radical cations. The geometrical parameters and atomic charges on various atomic sites of the DTT and DOT molecules and their radical cations suggest extended conjugation in these systems. Contrary to this, for the DOO⁺ and DTO⁺ ions there is no evidence in favour of such conjugation, however, the neutral molecules exhibit some conjugation. Harmonic forced field and vibrational mode calculations provided convincing theoretical evidence for the reassignment of some fundamental vibrational modes for all the four molecules. In going from the neutral species to the charged ions for all the four cases the CC stretching frequency is found to decrease drastically. The CS stretching frequency reduces drastically for the DTT and DOT molecules as compared to their radical cations whereas the CO stretching frequency is found to increase in going from the neutral molecule to its radical cation for the DOO and DTO molecules. The ring stretching mode with a₁ symmetry and CC and CO/S stretching modes in these molecules appear to help in conversion of neutral molecule into respective radical cation and neighbouring radical cation into respective neutral molecule. Thus, there appears the feasibility of stretching vibrational mode coupling with electron transfer.     

Vibrational Spectroscopic Study on Ion Solvation and Ion Association of Lithium Tetrafluoroborate in 4‐Ethoxymethyl‐ethylene Carbonate

应用红外及拉曼光谱研究了不同浓度的四氟硼酸锂在4-乙氧甲基-碳酸乙烯酯溶剂中的离子溶剂化和离子缔合现象。环形变谱带和羰基伸缩振动谱带的分裂,以及骨架环振动谱带的迁移和分裂表明,锂离子与溶剂分子间存在着较强的相互作用,这种相互作用是通过溶剂羰基氧原子实现的。利用光谱拟合技术定量计算了表观溶剂化数。随着电解质锂盐浓度的增加,溶剂化数逐渐由4.32降至1.26。此外,四氟硼酸根v1谱带的分裂表明在高浓度溶液中存在着光谱自由的四氟硼酸根、直接接触离子对和离子对二聚体。     

Efficient π-electron conjugated push-pull nonlinear optical chromophore 1-(4-methoxyphenyl)-3-(3,4-dimethoxyphenyl)-2-propen-1-one: A vibrational spectral study

As part of the efforts for the design new organic nonlinear optical (NLO) materials with high efficiency for present day technological requirements, a comprehensive investigation on the intramolecular charge transfer (ICT) of an efficient π-conjugated potential push-pull NLO chromophore, 1-(4-methoxyphenyl)-3-(3,4-dimethoxyphenyl)-2-propen-1-one to a strong electron acceptor group through the π-conjugated bridge has been carried out from their vibrational spectra. The NIR FT-Raman and FT-IR spectra supported by the density functional theory (DFT) quantum chemical computations have been employed to analyze the effects of intramolecular charge transfer on the geometries and the vibrational modes contributing to the linear electro-optic effect of the organic NLO material. The calculated first hyperpolarizability of DMMC is 6.650 × 10⁻³⁰ esu, which is 25 times that of urea. The simultaneous IR and Raman activation of the phenyl ring modes of ν(CC/C-C) mode, ring CC stretching modes, in-plane deformation modes and the umbrella mode of methyl groups also provide evidences for the charge transfer interaction between the donors and the acceptor group through the π-system. Vibrational analysis indicates the electronic effects such as induction and back-donation on the methyl hydrogen atoms causing the lowering of stretching wavenumbers have also been analyzed in detail. The planar conformations would give an enhanced NLO activity where as any deviations from planarity would decrease the mobility of electrons within the π-conjugated molecular system, resulting a reduction in NLO activity.     

Cyclopropyl- and Allyl-substituted Arenes in Reaction with Dinitrogen Tetroxide. Effect of Substrate Oxidation Potential on Reaction Direction

A correlation was found between oxidation potentials of acylcyclopropanes in solution (in CH₂Cl₂ and CH₃CN) and their HOMO energies calculated by semiempirical (AM1) and nonempirical (HF/6-31G and HF/6-31G**) methods. The correlation provides a possibility to forecast the reaction direction of the mentioned substrates and N₂O₄. The correlation possesses a general character. It was established for instance that arylcyclo-propanes, cyclopropylmethyl- and allylbenzenes oxidized at more positive potentials than reduction potential of NO⁺ and having more positive e_HOMOthan 9.0 eV (AM1), 8.4 eV (HF/6-31G), and 8.3 eV (HF/6-31 G**) reacted with N₂O₄ following the mechanism "electron transfer radical pair recombination" affording nitroaromatic derivatives retaining the cyclopropane (or allyl) fragments. Substrates of the same type where the electron transfer to NO⁺ should be endothermic process and whose HOMO values are less than the above critical numbers react with N₂O₄ by the mechanism of electrophilic cyclopropane ring opening (with aryl and benzylcyclopropanes) or by electrophilic addition across the double C=C bond (with allylbenzenes).     

Experimental and Theoretical Investigation of Vibrational Spectra of Coordination Polymers Based on TCE‐TTF

The room‐temperature infrared and Raman spectra of a series of four isostructural polymeric salts of 2,3,6,7‐tetrakis(2‐cyanoethylthio)‐tetrathiafulvalene (TCE‐TTF) with paramagnetic (Co^II, Mn^II) and diamagnetic (Zn^II, Cd^II) ions, together with BF₄^? or ClO₄^? anions are reported. Infrared and Raman‐active modes are identified and assigned based on theoretical calculations for neutral and ionized TCE‐TTF using density functional theory (DFT) methods. It is confirmed that the TCE‐TTF molecules in all the materials investigated are fully ionized and interact in the crystal structure through cyanoethylthio groups. The vibrational modes related to the C?C stretching vibrations of TCE‐TTF are analyzed assuming the occurrence of electron–molecular vibration coupling (EMV). The presence of the antisymmetric C?C dimeric mode provides evidence that charge transfer takes place between TCE‐TTF molecules belonging to neighboring polymeric networks.     

OH stretching force constants in complexes of water with F−, Cl−, Li+ ions and LiF,LiCl ion pairs by 6-31G ab initio MO calculations

Ab initio MO calculations using 6-31G and 6-31 + G (for complexes with F⁻ and LiF) basis sets have been carried out for complexes of H₂O (monomer and dimer) with F⁻, Cl⁻, Li⁺ ions as well as with LiF and LiCl ion pairs for the evaluation of the OH stretching force constants. The changes in force constants are discussed in terms of molecular interactions, cooperativity effect and interionic electrostatic interactions. It is noticed that the cooperativity effect also operates through ionic bonds in symmetrically hydrated ion pairs and that OH stretching force constants are found to increase in the case of solvent bound ion pairs and symmetrically hydrated halide ions showing anticooperativity effect.     

Elucidating Interactions between DMSO and Chelate‐Based Ionic Liquids

The C?D bond stretching vibrations of deuterated dimethyl sulfoxide ([D₆]DMSO) and the C₂?H bond stretching vibrations of 1,1,1,5,5,5‐hexafluoropentane‐2,4‐dione (hfac) ligand in anion are chosen as probes to elucidate the solvent–solute interaction between chelate‐based ionic liquids (ILs) and DMSO by vibrational spectroscopic studies. The indirect effect from the interaction of the adjacent S=O functional group of DMSO with the cation [C₁₀mim]⁺ and anion [Mn(hfac)₃]^? of the ILs leads to the blue‐shift of the C?D stretching vibrations of DMSO. The C₂?H bond stretching vibrations in hfac ligand is closely related to the ionic hydrogen bond strength between the cation and anion of chelate‐based ILs. EPR studies reveal that the crystal field of the central metal is kept when the chelate‐based ILs are in different microstructure environment in the solution.