聚并苯的链间作用对其导电能力的影响

采用量子化学晶体轨道ＣＮＤＯ／ ２ 方法,在考虑聚并苯链间作用的基础上对聚并苯双链模型的电子结构进行计算和讨论．结果表明：聚并苯链处于不同相对位置的链间作用对聚并苯的电荷分布规律及能带结构均有一定影响,位置不同,影响不同．从聚并苯的能带结构可以得出：聚并苯是有较小能隙、良好本征导电性能的半导体材料,考虑链间作用,对能带结构特征未有大的改变,能隙等值略有修正,导电能力有所加强．利用此模型讨论,更接近于晶体的真实结构,对进行聚并苯导电材料的性能改进将有一定帮助．     

硫化反式聚异戊二烯电子性质的理论化学研究

应用量子化学计算方法,对反式聚异戊二烯本征态和硫化态结构的能量及电子性质等进行了计算.结果表明,当聚异戊二烯掺杂硫后,相邻两链之间的距离a⊥变窄,体系的总能量降低,从而使整个掺杂体系更加稳定.另外,在硫化聚异戊二烯分子中,S原子位于两个相邻聚异戊二烯链之间,并偏向于其中一个分子链的C C双键的一侧,即与相邻两链中相对应的两个C C双键形成π-p-π共轭体系,增加了电子在两个聚异戊二烯链间的流动性,从而使硫化的反式聚异戊二烯更加稳定.另外,根据固体能带理论,采用量子化学EHMO方法,对反式聚异戊二烯本征态和硫掺杂态的能带结构进行了计算,根据硫化前后能隙和带宽的变化,解释了反式聚异戊二烯掺杂后呈现电导率各向异性的原因.     

聚肽分子链构象转变研究

聚肽分子链在一定的条件下可发生右旋分子链构象与左旋分子链构象间的构象转变 .文中提出了一个有关这一现象的统计理论解释 ,理论包含了两个重要的参数γ、ρ .γ与右旋和左旋分子链构象间能量差别有关 ;ρ与在左旋分子链段中启始一个右旋构象的结构单元所需能量有关 .进一步考虑了体系中酸分子存在对构象转变的影响 ,以解释新近发现的聚肽左、右旋多重分子链构象转变现象 .此外 ,运用核磁共振 (NMR)手段还对这一现象做了进一步的研究 .通过与实验结果和文献中报告的数据比较 ,证明这一理论可以很好地解释聚肽分子链中发生的左、右旋分子链构象转变     

聚羧酸共聚物侧链结构对水泥分散性的研究

通过“分子设计”,研制出一类带有不同侧链的聚醚基团,羧酸基团的聚羧酸共聚物减水剂,着重讨论了侧链长度对分散性能的影响。实验结果表明：通过调整聚羧酸共聚物中不同侧链的比例使其具有最佳的分散性。本实验合成的聚乙二醇侧链分子量为600：400=1：1（摩尔比）时,聚羧酸共聚物的分散效果最好,水泥浆体的流动度及分散力最佳,分别为289mm和10．36。     

双端正离子活性链的研究——α,ω—二胺基聚丁二醇-聚酯-聚丁二醇三嵌段低聚物的合成

<正> 本实验室前项工作曾证明用脂肪二酰氯与高氯酸银引发四氢呋喃(THF)在0—50℃下聚合可形成没有链终止和链转移反应的活性聚合链.为了减少聚丁二醇醚结晶趋势,又制备了双端活性的THF-环氧丙烷无规共聚醚链.本文则通过THF的开环聚合,将一个非“活性”的聚酯转变成为双端活性链,合成了伯胺端基聚丁二醇-聚酯-聚丁二醇遥爪低聚物,并用以增韧环氧树脂.     

旋光性聚甲基丙烯酸三苯甲酯的合成

<正> 旋光性聚甲基丙烯酸三苯甲酯(PTrMA,A)是一种新型旋光聚合物,其旋光性不是来自结构单元中的手性原子或基因,而是刚性的分子链呈长程单向螺旋构象,使分子链获得手征性的结果.自70年代末问世以来,在改进其合成方法和作为色谱固定相直接拆分手性化合物的应用方面受到人们注意,由于独特的结构,可以设想,如果将它带上特殊     

端基对侧链型偶氮聚电解质自组装膜内生色团取向的影响

用偏振紫外光谱研究了 4种带有不同端基的侧链型偶氮聚电解质静电逐层自组装膜中偶氮生色团的初始取向 .讨论了不同的端基对偶氮生色团在自组装膜中初始取向的影响 .进一步探讨了偶氮聚电解质自组装膜的结构特点 .研究表明 ,侧链型偶氮聚电解质自组装膜中偶氮生色团普遍存在一定程度的沿面取向 .偶氮生色团所带端基的类型对其在自组装膜中的取向程度有较大的影响 ,这主要取决于偶氮生色团与聚阳离子基底的电荷相互作用和极性相互作用等 .对偶氮生色团在水溶液中能形成H 聚集体的自组装膜来说 ,H 聚集体对生色团取向也有一定的影响 .结果表明 ,在制备需控制生色团取向性的自组装膜时 ,要考虑生色团上的不同端基对取向的影响     

超支化聚碳硅氮烷的合成与表征

聚碳硅氮烷是一种新型含硅有机金属聚合物,其主链由硅氮碳连接而成,侧链为有机基团;与其它含硅聚合物(聚硅氮烷、聚碳硅烷等)类似,聚碳硅氮烷适于用做力学性能极佳且耐高温氧化的氮化硅(Si3N4)和氮化硅/碳化硅(Si3N4/SiC)复相陶瓷的前驱体.[1]超支化聚合物具有溶解性好、粘度低     

聚亚甲基链的温度系数

本文采用旋转异构态模型,考虑排斥体积效应,用 Monte Carlo模拟方法计算了聚亚甲基高分子链的温度系数dln/dT。考虑排斥体积的聚亚甲基链的温度系数大于无扰聚亚甲基链的温度系数,并更接近实验值。     

螯合树脂研究 Ⅶ.含聚硫醚主链的多乙烯多胺型螯合树脂的合成及其吸附性能

含硫、氮配位原子的螯合树脂对贵金属具有良好的吸附性能。本工作合成的以聚硫醚为主链,侧链为多乙烯多胺的树脂尚未见文献报道。这类树脂硫、氮含量较高,主链和侧链均能对贵金属离子起络合作用,故对Au~(3+)、Ag~+、Pd~(2+)、Pt~+等具有较强的吸附能力。树脂的合成路线和预期的主要结构如下。     

Intermolecular covalent pi-pi bonding interaction indicated by bond distances, energy bands, and magnetism in biphenalenyl biradicaloid molecular crystal

Density-functional theory (DFT) calculations were performed for energy band structure and geometry optimizations on the stepped pi-chain, the isolated molecule and (di)cations of the chain, and various related molecules of a neutral biphenalenyl biradicaloid (BPBR) organic semiconductor 2. The dependence of the geometries on crystal packing provides indirect evidence for the intermolecular covalent pi-pi bonding interaction through space between neighboring pi-stacked phenalenyl units along the chain. The two phenalenyl electrons on each molecule, occupying the singly occupied molecular orbitals (SOMOs), are participating in the intermolecular covalent pi-pi bonding making them partially localized on the phenalenyl units and less available for intramolecular delocalization. The band structure shows a relatively large bandwidth and small band gap indicative of good pi-pi overlap and delocalization between neighboring pi-stacked phenalenyl units. A new interpretation is presented for the magnetism of the stepped pi-chain of 2 using an alternating Heisenberg chain model, which is consistent with DFT total energy calculations for 2 and prevails against the previous interpretation using a Bleaney-Bowers dimer model. The obtained transfer integrals and the magnetic exchange parameters fit well into the framework of a Hubbard model. All presented analyses on molecular geometries, energy bands, and magnetism provide a coherent picture for 2 pointing toward an alternating chain with significant intermolecular through-space covalent pi-pi bonding interactions in the molecular crystal. Surprisingly, both the intermolecular transfer integrals and exchange parameters are larger than the intramolecular through-bond values indicating the effectiveness of the intermolecular overlap of the phenalenyl SOMO electrons.     

Modeling of real 20-component protein chains: Determination of the electronic density of states of aperiodic seven-component polypeptide chains containing strongly different amino acid residues

To model a real 20-component protein chain, the results of the electronic density of states (DOS ) of seven-component periodic and aperiodic polypeptide chains calculated on the basis of ab initio matrix block negative factor counting method are presented. The seven amino acid residues taken into account are rather different: glycine, serine, cysteine, asparagine, histidine, aspartic acid, and tryptophane. In the case of aperiodic chains, the energy states are found to be distributed over a much wider range of energy than in the corresponding periodic chains. In the intrinsic state, both periodic and aperiodic polypeptide chains are predicted to be insulators. The effect of the block copolymerization on the DOS distribution and the band gap values of both periodic and aperiodic polypeptide chains has been also investigated. Finally, the methods to calculate from the DOS curves hopping conductivities and the possibilities to compare them with experiment are outlined.     

Semiconductor behavior of a metal-organic framework (MOF)

Upon light excitation MOF-5 behaves as a semiconductor and undergoes charge separation (electrons and holes) decaying in the microsecond time scale. The actual conduction band energy value was estimated to be 0.2 V versus NHE with a band gap of 3.4 eV. Photoinduced electron transfer processes to viologen generates the corresponding viologen radical cation, while holes of MOF-5 oxidizes N,N,N',N'-tetramethyl-p-phenylenediamine. One application investigated for MOF-5 as a semiconductor has been the shape-selective photocatalyzed degradation of phenol in aqueous solutions.     

First-principles study of a new type nanojunction: Finite length carbon chain inserted into half of a carbon nanotube

Based on first-principles calculations, we investigate the structure and electronic properties of a carbon atomic chain in finite length inserted into half of a single walled carbon nanotube (SWCNT), which we called half chain@SWCNT or more generally HCS. Comparing the optimized structure of HCS with that of the same chiral indices SWCNT and all carbon chain inserted SWCNT, we find that the geometry of the tube in HCS is slightly altered due to the weakly interacting between the inserted chain and the outer tube wall of HCS. Our calculation of band structure indicates that the armchair (5, 5) HCS exhibits metallic character, which is as that of (5, 5) SWCNT and all carbon chain inserted (5, 5) SWCNT. The zigzag (8, 0) and (9, 0) HCSs have small change in the energy gap compared to the corresponding pristine ones. Due to the downshift of conduction bands originating from the carbon chain, the calculation of band structure shows that chiral (6, 4) HCS is a semiconductor system with a small band gap of 0.94 eV, less than 1.125 eV in pristine SWCNT. The studied HCSs with unique structure and electronic property may construct a new generation nanoscale junctions without the usual heptagon–pentagon defect pair considerations.     

硅锗酞菁聚合物的电子结构

在自洽场晶体轨道法全略微分重叠(SCFCNDO/2－CO)水平上对氧桥和硫桥一维链硅锗酞菁聚合物的能带结构和电子特性进行了研究,探讨了堆积酞菁环间交错角以及中心原子和桥原子的变化对电子特性的影响.计算结果表明,除前线带宽外,交错角变化对所研究的聚酞菁电子特性影响不大.晶体轨道分析表明,氧桥聚酞菁电荷载流子主要通过垂直酞菁环π轨道的纵向重叠导电通路流动,而硫桥聚酞菁导带电子还可经中心原子和桥原子的d轨道重叠通路迁移.     

Determination of defect states in semiconductor nanocrystals by cyclic voltammetry

Colloidal, monodisperse CdSe nanocrystals were homogeneously dispersed in an ionic liquid and investigated by means of cyclic voltammetry. Almost all known defect states in semiconductor nanocrystal were quantitatively measured with this nonoptical method (including nonradiative defect states). Variation of the illumination and temperature resulted in excitation of defect-trapped electrons into the conducting band. Thus, we succeeded for the first time to correlate defect states in nanocrystals with those in the corresponding bulk crystals.     

弹性竿模型下超螺旋DNA分子的构象研究

采用弹性竿模型 (Elasticrodmodel) ,用MonteCarlo方法对DNA分子的构象进行研究 .通过计算发现 ,DNA分子的能量是由弯曲势能EB 和扭转势能ET 两部分组成 ,通常EB 比ET 大一至两个数量级 .同时给出了均方回转半径与链长之间的关系为〈R2g〉 =1 1 69 5 -3 5×n +0 0 2 5×n2 ,它体现了DNA分子结构的特点 .验证了公式Lk=Wr+Tw ,得出Lk与Wr比较接近的结论 ,考虑DNA分子的构型 ,意味着DNA分子容易被弯曲而不易被扭转 ,但随着连接系数的增加 ,DNA被扭转的几率也在增加 .这为分析DNA分子的结构特征提供了一种新方法     

Environment-controlled interchromophore charge transfer transitions in dipeptides probed by UV Absorption and electronic circular dichroism spectroscopy

Charge transfer (CT) transitions between the C-terminal carboxylate and peptide group have been investigated for alanyl-X and X-alanine dipeptides by far-UV absorption and electronic circular dichroism (ECD) spectroscopy (where X represents different amino acid residues). The spectra used in the present study were obtained by subtracting the spectrum of the cationic species from that of the corresponding zwitterionic peptide spectrum. These spectra displayed three bands, e.g., band I between 44 and 50 kK (kK = 10(3) cm(-1)), band II at 53 kK, and band III above 55 kK, which were, respectively, assigned to a n(COO-) --> pi* CT transition, a pi(COO-) --> pi* CT transition, and a carboxylate pi --> pi* (NV1) transition, respectively By comparison of the intensity, bandwidth, and wavenumber position of band I of some of the investigated dipeptides, we found that positive charges on the N-terminal side chain (for X = K), and to a minor extent also the N-terminal proton, reduce its intensity. This can be understood in terms of attractive Coulomb interactions that stabilize the ground state over the charge transfer state. For alanylphenylalanine, we assigned band I to a n(COO-) --> pi* CT transition into the aromatic side chain, indicating that aromatic side chains interact electronically with the backbone. We also performed ECD measurements at different pH values (pH 1-6) for a selected subset of XA and AX peptides. By subtraction of the pH 1 spectrum from that observed at pH 6, the ECD spectrum of the CT transition was obtained. A titration curve of their spectra reveals a substantial dependence on the protonation state of the aspartic acid side chain of AD, which is absent in DA and AE. This most likely reflects a conformational transition of the C-terminus into a less extended state, though the involvement of a side chain --> peptide CT transition cannot be completely ruled out.     

电荷转移复合分子晶体TMPD·(TCNQ)2的电子能带结构及其与NMP·TCNQ和TTF·TCNQ的比较

本文对电荷转移复合分子晶体TMPD·(TCNQ)_2的电子能带进行了计算。在计算中将TMPD及TCNQ分别作为准一维分子柱来处理。所用计算方法为EHMO/LCAO-MO-CO方法。计算结果再次证实我们在前文给出的规律, 即分子晶体能带的位置由其孤立分子相应分子轨道能级的位置决定, 而能带宽度由相邻分子的相应分子轨道间的相互作用决定。本文还对该晶体的能带结构及其与室温电导率的关系进行了讨论, 并与NMP·TCNQ 和TTF·TCNQ晶体的进行比较。     

Photo-assisted electron injection at a semiconductor—NH3 interface

Illumination of a p-type semiconductor—NH₃ interface (or heterojunction) with photons of energy greater than the semiconductor band gap causes electrons to be injected into the NH₃. There is no hole injection at a n-type electrode. Suggestions are made for the required energy levels in the liquid.