扩环荧光碱基类似物x-腺嘌呤分子基态和激发态性质的理论研究

近年来, 设计合成荧光碱基类似物成为科学家研究的一个热点. 利用含时密度泛函理论考察了腺嘌呤类似物x-腺嘌呤的电子激发态性质, 计算了其电子吸收光谱和荧光光谱, 并对其若干低能电子激发态进行了详细解析归属. 同时考察了甲醇溶剂、糖环和与胸腺嘧啶配对对其光谱性质的影响. 研究表明, 在低能区域, x-腺嘌呤的吸收光谱与天然腺嘌呤相比发生了很大红移, 使其可以被选择性地激发. 计算得到的吸收光谱和荧光光谱与实验值符合很好. 溶剂化和糖环对x-腺嘌呤的电子吸收光谱具有增色效应, 同时发现溶剂化和糖环均使其荧光发生红移, 而碱基配对对其最低激发态ππ^* 和荧光发射无显著影响, 但使其最低nπ^* 态发生显著蓝移. 关键词： x-腺嘌呤')" href="#">x-腺嘌呤 电子吸收光谱 荧光光谱 含时密度泛函     

桥基取代2,7’-(乙烯基)-二-8-羟基喹啉类化合物的密度泛函理论研究

在B3LYP/6-31G(d)水平上对2,7′-(乙烯基)-二-8-羟基喹啉(2,7′-Ethq_2)及其6种桥基取代物的几何结构进行了全优化,探讨了取代基对分子的结构、电荷转移、前线分子轨道能级、能隙等方面的影响.采用含时的密度泛函理论(TD-DFT)研究各分子的气相及液相中的电子光谱,分析光谱的变化规律.结果表明,取代基的电子效应和立体效应对取代物的电子结构和电子光谱有重要影响,取代基重新调整了2,7′-Ethq_2的原子电荷布居,改变了前线分子轨道能隙,导致吸收光谱发生变化.氨基和氰基对2,7′-Ethq_2影响较为显著,吸收波长红移较大.此外溶剂的极性对其电子光谱也有影响,随溶剂极性的增大,硝基取代物的最大吸收波长发生明显的红移,其它取代物的最大吸收波长均发生较小的蓝移.     

旋转异构和键长变化对溶液中FTC分子光谱性质的影响

采用含时密度泛函理论结合极化连续模型计算了不同溶剂环境下FTC分子各旋转异构体的单光子吸收光谱. 结果显示在气态和溶剂中,各异构体的最大吸收波长均存在大约30 nm的差别. 在不同溶剂中,各异构体的能量次序和相应的玻尔兹曼统计分布几率发生了较大变化. 基于Hartee-Fock方法优化的结构,计算了玻尔兹曼统计平均吸收光谱,结果与实验符合得很好. 计算表明,对于所研究的分子体系,键长变化对分子的光谱性质有重要影响.     

C78O5稳定性和光谱的理论研究

用半经验AM1和INDO/CIS方法及密度泛函方法在C2v-C78基础上研究了C78O5可能异构体的平衡构型和光谱性质．C78O5的最稳定异构体是具有一个轮烯和四个环氧结构的异构体28,29,30,31,52,53,70,71,73,78-C78O5(A)．C78O5异构体电子光谱与C2v-C78相比将发生蓝移，并讨论了蓝移的原因，并对电子跃迁进行指认．基于B3LYP/6-31G优化构型，用AM1和B3LYP/6-31G方法探讨了C78O5的IR和NMR谱．     

Theoretical Studies on Electronic Structures and Spectroscopy of Fluorescent Arylamino Fumaronitrile

设计了一系列发荧光的芳胺氰化物, 并用密度泛函方法在B3LYP/6-31G*水平上进行几何构型优化．在优化构型基础上,分别用INDO/CIS、AM1、CIS-ZINDO TD和B3LYP/6-31G*方法计算了芳胺氰化物的电子光谱、红外光谱、荧光光谱及核磁共振碳谱．结果表明,与母体相比,由于萘环较大的立体效应使氰化物的能隙变宽,荧光光谱及电子光谱的主要吸收峰发生蓝移．而由于电子被分散到萘环上,氰化物的主要红外频率发生红移．相反,羟基的存在改善了分子的对称性,扩展了共轭体系,使能隙变窄,荧光光谱及电子光谱的主要吸收峰发生红移．同时由于羟基的供电效应,C-H伸缩振动发生蓝移．     

溶剂和外电场下N-羟乙酰神经氨酸的理论光谱研究

通过密度泛函理论对非人源性的红肉危害因子N-羟乙酰神经氨酸(Neu5Gc)在溶剂和外电场下的分子光谱性质进行研究.以M062X/6-311+G(d, p)水平在不同介电常数溶剂(苯ε=2.27,乙酸ε=6.2528,乙醇ε=24.85,甲酸ε=51.10,水ε=78.35)和气相条件下完成几何结构优化、红外、拉曼光谱模拟,相应的,在M062X/6-311G (d, p)水平进行笛卡尔坐标X轴正方向不同强度外电场(0, 0.005, 0.01, 0.015, 0.02, 0.025 a.u.)下的对比计算.基于各自优化后结构在PBE1PBE/TZVP水平模拟了Neu5Gc在溶剂和外电场下的紫外光谱.结果表明,溶剂下Neu5Gc因溶液极性和与溶质分子间相互作用使其结构稳定性降低,红外和拉曼光谱均产生一定蓝移,在乙醇、甲酸、水相下O-H红外收缩振动频率增高;紫外最大吸收波长为乙酸时183.26 nm,其主要是HOMO到LUMO+1轨道的跃迁.电场下Neu5Gc的红外和拉曼光谱因诱导偶极效应差异较大,在0.025 a.u.时C-H键拉曼活性达到最大,伴随红外光谱蓝移;0.025 a.u.时,紫外激发能最低,紫外最大吸收波长为189.63 nm,主要是HOMO-4和HOMO-1到LUMO+1轨道的跃迁.     

溶剂和外电场下N-羟乙酰神经氨酸的理论光谱研究

通过密度泛函理论对非人源性的红肉危害因子N-羟乙酰神经氨酸(Neu5Gc)在溶剂和外电场下的分子光谱性质进行研究.以M062X/6-311+G(d,p)水平在不同介电常数溶剂(苯ε=2.27，乙酸ε=6.2528，乙醇ε=24.85，甲酸ε=51.10，水ε=78.35)和气相条件下完成几何结构优化、红外、拉曼光谱模拟，相应的，在M062X/6-311G (d,p)水平进行笛卡尔坐标X轴正方向不同强度外电场(0,0.005,0.01,0.015,0.02,0.025 a.u．)下的对比计算.基于各自优化后结构在PBE1PBE/TZVP水平模拟了Neu5Gc在溶剂和外电场下的紫外光谱.结果表明，溶剂下Neu5Gc因溶液极性和与溶质分子间相互作用使其结构稳定性降低，红外和拉曼光谱均产生一定蓝移，在乙醇、甲酸、水相下O-H红外收缩振动频率增高;紫外最大吸收波长为乙酸时183.26 nm，其主要是HOMO到LUMO+1轨道的跃迁.电场下Neu5Gc的红外和拉曼光谱因诱导偶极效应差异较大，在0.025 a.u．时C-H键拉曼活性达到最大，伴随红外光谱蓝移; 0.025a.u．时，紫外激发能最低，紫外最大吸收波长为189.63 nm，主要是HOMO-4和HOMO-1到LUMO+1轨道的跃迁.     

两种新香豆素分子的热力学和光谱性质

使用密度泛函理论方法在B3LYP /6-31++G**理论水平对两种香豆素a和b分子的几何结构、光谱、热力学性质进行理论计算研究,并基于Tomasi的极化统一场模型(PCM)讨论溶剂效应。结果显示,香豆素a和b分子在气相中的最低能量吸收波长分别为352和355 nm,溶剂及其极性大小对香豆素a最低能量吸收波长影响很小,但在溶剂作用下香豆素b分子的最低能量吸收波长红移7-10 nm,溶剂的极性对该波长影响较小。298 K标准压力下香豆素a和b分子的气态标准摩尔生成焓 分别为-1373.171和-1310.805 kJ.mol-1,标准摩尔生成自由能 分别为-1064.043和-1035.849 kJ.mol-1,标准摩尔熵 分别为763.910和742.150 J.mol-1.K-1.     

脱氢枞酸基D-A型分子的合成、空间构型及光谱性能

对三苯胺进行溴代和C-N偶联反应合成4-萘基三苯胺(a),对脱氢枞酸进行酯化、溴代、硝化、还原和C-N偶联反应合成13-[N,N-(4-萘基苯基)-苯基]胺基-脱异丙基脱氢枞酸甲酯(b)及13-[N,N-双(4-萘基苯基)]胺基-脱异丙基脱氢枞酸甲酯(c)两个化合物,通过1H MNR,13C MNR及MS对化合物的结构进行表征。为了研究化合物结构与光谱性能之间的关系,首先利用Gaussian 09程序采用密度泛函DFT/B3LYP方法,对三个化合物的空间构型进行全优化,得到它们的键长、键角和二面角,对比发现脱氢枞酸骨架和萘环的引入会影响化合物的共平面性,而萘环的引入会增大化合物的共轭程度。光谱性能方面,研究了三种化合物在甲醇、二氧六环、四氢呋喃、二氯甲烷和环己烷这5种极性逐渐减小的溶剂中的荧光发射光谱和紫外吸收光谱。结果表明,在荧光光谱中,化合物a,b和c在不同极性溶剂中最大荧光发射波长均有不同程度位移,在甲醇中最大,在环己烷中最小,但是位移并非随着极性的增大而只发生红移,在二氯甲烷、四氢呋喃和二氧六环3种极性依次增大的溶剂中,a,b,c的荧光发射波长均随着溶剂极性的增大而发生较大程度的蓝移;在同一溶剂中,化合物b和c相对于a的荧光发射波长依次发生红移,c的红移程度与b差距不大。紫外吸收光谱中,三个化合物在不同极性溶剂中的最大吸收波长也有差异,在200～250 nm区间,三个化合物均在二氯甲烷中有较大位移,在300～350 nm区间,在甲醇中位移较大,而在250～300 nm区间,最大吸收波长差别不大;在同一溶剂中,它们在300～350 nm区间的最大吸收波长差别较大,化合物c较a红移26 nm。结合结构优化所得数据可以证明,化合物的共轭程度对荧光发射光谱和紫外吸收光谱均有影响,而共平面性对荧光发射光谱影响较大。化合物a,b和c在不同极性溶剂中荧光发射光谱和紫外吸收光谱的较大变化,表明它们有明显的溶致变色行为,具有作为分子探针探测外部环境极性大小的潜能。     

C78O异构体的电子结构和光谱

为了模拟C78单加成物的加成位置和稳定性,并预测其光谱性质,用INDO系列方法对基于C2v-C78之上的C78O所有可能的34个异构体结构和电子光谱进行理论研究．结果表明,C78O的最稳定异构体是O加在位于C2v-C78短轴上的73,78-键上且形成环氧结构的6／6异构体,O的原子轨道对73,78-C78O中的HOMO能量降低起重要作用．讨论了电子跃迁性质和73,78-C78O电子光谱的长波吸收峰与母体相比发生蓝移的原因．     

Solvent Polarity and Excitation Wavelength Dependence of the Dual Fluorescence in N,N-Diethyl-4-Nitrosoaniline

Dual fluorescence in N,N-Diethyl-4-nitrosoaniline (DENA) has been studied employing absorption, excitation and emission spectroscopic techniques and computational methods. The absorption and fluorescence spectra of DENA were measured in solvents of various polarities at room temperature. The emission spectra of DENA were found to exhibit a single emission band in non polar solvent (cyclohexane) and in a highly polar solvent (acetonitrile). In the contrary, two emission bands were observed in medium polar solvents (tetrahydrofuran, 1,2-dichloroethane and dichloromethane) whereby the short (local excited; LE) and long (charge transfer; CT) emission maxima correspond to the emission maxima of the compound observed in cyclohexane and acetonitrile solutions, respectively. Moreover, the two emission bands have shown strong excitation wavelength dependence, and area normalization resulted in an iso-emissive point. The two emission maxima were in addition found to correspond to two excitation maxima in 3D fluorescence spectra. Further, two minima were obtained in potential energy surface calculation of DENA. From the experimental and computational results it was concluded that the dual fluorescence may be attributed to the presence of two different ground state structural conformers of DENA in equilibrium that are stabilized through solute-solvent interaction.     

Excited state intramolecular proton transfer of 1,2-dihydroxyanthraquinone by femtosecond transient absorption spectroscopy

1,2-Dihydroxyanthraquinone (alizarin) shows dual emission bands with a large Stokes shift from a “locally-excited (LE)” and “proton-transferred (PT)” tautomers in the excited state. Excited state intramolecular proton transfer (ESIPT) reaction of alizarin is tunable by changing concentration, solvent polarity, excitation wavelength, and etc. ESIPT reaction of alizarin in the excited state was investigated by steady-state absorption/emission spectroscopy and femtosecond transient absorption spectroscopy. In ethanol solution, the lifetime of PT tautomer of alizarin was measured as 87 ps, in addition to 0.35 and 8.3 ps vibrational cooling dynamics for the LE and PT tautomers of alizarin, respectively. In binary mixtures of ethanol and water, the excited state dynamics became more complicated; the LE and PT tautomers appeared to decay with 8.9 and 30.8 ps lifetimes, which is much shorter compared to the lifetime of the PT tautomer in ethanol. A long-lived nonradiative state in the excited states of alizarin was found as well, which was proposed as a “trapped” state with tightly hydrogen-bonded water molecules. The ESIPT reaction of alizarin was blocked in a 1:1 mixture of ethanol-water due to strong hydrogen bonding between water molecules and alizarin, which was further confirmed by the efficient coupling of alizarin to TiO₂ nanoparticles in the 1:1 binary mixture of ethanol-water.     

Spectroscopic study of a representative polar cap of buckminsterfullerene: Cyclopentacorannulene

The spectroscopic properties of corannulene and cyclopentacorannulene are examined by use of absorption and steady-state fluorescence measurements. A red shift in the emission maxima of cyclopentacorannulene is noted with respect to the emission maxima in the corannulene spectrum. Similar differences in the absorption spectra of both molecules are also observed. Reasons for the dissimilarities in the absorption and emission spectra of these molecules are discussed. The fluorescence quantum yields and lifetimes of the molecules measured in organic solvents are reported. The fluorescence quantum yield and lifetime of cyclopentacorannulene are lower than those of corannulene. This difference is attributed to the highly strained and nonplanar structure of cyclopentacorannulene. The effectiveness of nitromethane as a quencher of corannulene and cyclopentacorannulene fluorescence is examined. In contrast to previously reported results, the fluorescence of these molecules is quenched by nitromethane. Fluorescence quenching of the molecules has been attributed to complex formation in the ground state, i.e., static quenching.     

Effects of annealing on calcium tungstate crystals

The influence of annealing in different atmospheres on absorption and luminescent properties of high-quality undoped CaWO₄ single crystals is presented. The decreasing of green emission intensity after annealing in oxygen and air have been revealed, while two well-defined maxima near 25,000 and 32,000 cm⁻¹ can be observed in the induced absorption spectra. These maxima are attributed to the interstitial oxygen, possibly in the form of the O⁻-centre. The increase of the blue/green luminescence ratio has been revealed after annealing in nitrogen while the crystal transparency remains unaffected. The possible ways to reduce slow green emission component without changing crystal absorption are shown. Structure of colour centres and the models of revealed processes are discussed.     

基于密度泛函的甲醇和乙醇荧光特性研究

使用英国爱丁堡FLS920P荧光光谱仪,对甲醇、乙醇的紫外吸收光谱和荧光光谱进行实验检测,得到二者的光谱特征参数。分别采用密度泛函理论(DFT)和单激发组态相互作用(CIS)对二者分子的基态和激发态结构进行优化,并比较两种分子在不同能态下的差异。应用含时密度泛函理论(TD-DFT)的不同泛函结合极化连续介质模型(PCM)在6-31++G(d, p)水平上分别计算了二者的紫外吸收光谱和荧光光谱,与实验结果吻合。分析了甲醇、乙醇荧光产生机理,同时分析了不同泛函对于计算光谱的影响。结果表明：甲醇、乙醇在紫外波段有微弱吸收,在紫外激发下能产生拉曼峰和微弱的荧光峰。甲醇、乙醇的吸收光谱是由里德堡激发产生,产生荧光的轨道跃迁为σ*→π*。泛函OLYP能够较好地重现实验吸收能,而泛函MPWK能够较好地重现实验发射能,并且发现不同的纯泛函计算跃迁能也具有差异性。结果可为醇类分子的分子特性研究提供参考。     

The T-contribution to the electrical resistivity at low temperatures in NiAs-type Ni1−xS1−ySey

The y(1−y)-like maxima in Ni_0.98S_1−ySe_y are found beyond y_c in the y-dependences of the coefficient of the T² contribution to the resistivity and of the residual resistivity. Here, the critical concentration of the antiferromagnetic and less-conductive phase is determined to be y_c = 0.095.     

UV-spectral changes for some azo compounds in the presence of different solvents

The electronic absorption spectra of four azo dyes with different substituents (such as Cl, I, OH) are determined at room temperature in twenty-one solvents with different polarities. The electronic transitions of azo dyes are interpreted. Linear solvation energy relationships have been investigated for solvatochromic behaviors and solute-solvent interactions of azo dyes. Linear solvation energy relationships were performed by multiple linear regression analysis using dielectric function, refractive index function and Kamlet-Taft parameters. We have observed that the hydrogen bonding acceptor ability and the induction-dispersive forces of solvent molecules have caused the bathochromic shift in absorption maxima of azo dyes.     

Synthesis and Characterization of a Biologically Active Lanthanum(III)–Catechin Complex and DNA Binding Spectroscopic Studies

A lanthanum(III) complex of catechin has been synthesized and characterized by elemental analysis, molar conductance, UV-Vis spectra, infrared spectra, thermal analysis, and ¹H NMR. The complex behaves as a nonelectrolyte in methanol solvent. The spectral and thermal properties of the complex are examined. A thermogravimetric (TGA) study showed the hydrated nature of the complex. ¹H NMR spectra of the lanthanum and the catechin (CT) ligands measured in CD₃OD-d₄ also show metal ligand coordination. The lanthanum–catechin complex shows bright luminescence in methanol solution. The interaction of the complex with calf thymus DNA has been investigated by absorption and emission spectroscopic measurements. Experimental spectral results suggest CT–DNA binding with catechin complex via an intercalative mode.     

激发态分子内质子转移分子2-羟基-1-萘甲醛半碳酰腙的光谱特性

通过考察2-羟基-1-萘甲醛半碳酰腙(HNLSC)在不同极性溶剂中的吸收光谱和荧光光谱,详细研究了HNLSC分子在不同溶剂及酸、碱条件下的不同构型,证实了HNLSC具有典型的ESIPT特性。在非极性溶剂中分子主要以分子内氢键的闭式构型存在,这种闭式构型使分子具有ESIPT特性,在环己烷溶剂和高酸度极性溶剂中分子均表现出～415nm的正常荧光和～435nm处的反常ESIPT荧光。在极性质子溶剂中,因溶质和溶剂之间形成了分子间的氢键以及进一步去质子化,HNLSC形成了基态的溶剂化开式构型和离子构型,在吸收光谱中表现出～395nm的离子构型特征吸收。开式构型和离子构型阻断了分子内质子转移途径,因而在荧光光谱中仅表现出一个特征峰。实验进一步通过三乙胺和稀硫酸调节溶液体系的极性和酸度环境,证明在不同溶剂极性和酸度环境下,HNLSC分子不仅存在萘环上羟基变化引起的多种互变异构体间的转化平衡,同时存在—CHN—NH—CO—NH2结构域的烯醇式和酮式结构的相互转化。