光敏氧化还原反应 VI: 卟啉光敏还原甲基紫精的溶剂效应

本文报道水溶性卟啉在DMSO-H2O混合体系中光敏还原甲基紫精的最新结果. 本研究包括三个敏化剂: ZnTPRS、二羟基锡(IV)meso-四(p-磺酸苯基)卟啉(Sn TPPS)和ZnTMPyP. 在0,20,40,60和80%DMSO水溶液中比较了敏化剂光敏还原甲基紫精的能力, 观察到量子产率随DMSO的比例而增长.     

烷基紫精化合物的电氧化还原行为

用微分脉冲极谱法研究了烷基紫精及聚紫精的电氧化还原行为。紫精的烷基影响紫精化合物的还原电位及其还原产物在电位及其还极上的成膜性能。与低分子烷基紫精相比，烷基聚紫精的第一还原电位Ｅ１较正，两步还原反应的电位间隔△Ｅ较大，而且两步还原反应均有良好的可逆性。支持电解质的卤素离子对紫精化合物还原电位有影响，其影响能力的顺序为：Ｉ＾－＞Ｂｒ＾－＞Ｃｌ＾－＞Ｆ＾－。     

聚N－（4，4＇－联吡啶盐）－p－乙烯基吡啶的电还原及光还原行为

合成了三种新型的主链为聚４－乙烯基吡啶的侧链型紫精聚合物和相应的小分子紫精，研究了它们的电还原及光还原行为。结果表明这类侧链型紫精聚合物的电还原和在异丙醇水溶液中的光还原都存在明显的聚合物效应，还原后生成的自由基正离子分子内缔合的倾向比相应的小分子紫精大得多．     

聚N—（4,4‘—联吡啶盐）—p—乙烯基吡啶的电还原及光还原行为

合成了三种新型的主链为聚４－乙烯基吡啶的侧链型紫精聚合物和相应的小分子紫精，研究了它们的电还原及光还原行为。结果表明这类侧链型紫精聚合物的电还原和在异丙醇水溶液中的光还原都存在明显的聚合物效应，还后生成的自由基正离子分子内缔合的倾向比相应的小分子紫精大得多。     

紫精类电致变色材料的制备和机理

1,1'-二取代4,4'-联吡啶盐通常称作紫精(viologen),紫精以及接有紫精基团的聚合物（polyviologen）有优异的电致和光致变色性能,在新一代电致变色器件、显示器件和智能窗等方面有很好的应用前景。文章综述了紫精和紫精聚合物的制备、结构与性能、电致变色机理、功能器件设计以及在化学合成、纳米功能符合等方面的研究进展,并提出例如今后的重要研究方向。     

光敏氧化还原反应 Ⅵ.卟啉光敏还原甲基紫精的溶剂效应

近年来,对卟啉-甲基紫精-EDTA(乙二胺四乙酸)三组分体系的光敏电子转移反应已有了深入的研究.敏化反应产物MV~+与敏化剂卟啉正离子自由基之间的反向电子转移(backelectron transfer),被认为是影响MV~+产率的一个重要因素,因而如何促进初级电子转移后的电荷分离是这个领域的重要课题.在水溶液中,四(N-甲基吡啶)卟啉锌(ZnTMPyP~(4+))光敏还原甲基紫精的效率,要比meso-四(p-磺酸苯基)卟啉锌(znTPPS~(4-))高得多.这可解释为:前者带正电荷,与正电性的敏化产物MV~+有静电排斥作用,有利于电荷分离;而后者     

烷基链长对紫精分子在Cu(100)电极表面吸附结构的影响

用循环伏安法(CV)和原位扫描隧道显微镜(STM)研究了烷基取代的紫精分子在Cu(100)电极上的氧化还原行为及其吸附结构对电极电势的依赖性. 对乙基紫精(DHV)和庚基紫精(DEV)在含有KCl电解质溶液中进行循环伏安曲线的测定, 两者呈现出不同的氧化还原行为. 从STM所得图像观察, 二价庚基紫精在Cl-c(2×2)-Cu(100)电极上呈现出二维有序的点阵组装结构,而二价乙基紫精却未出现任何的吸附结构. 降低电极电势至单电子转移反应发生时, 形成的自由基庚基紫精在电极表面呈现出稳定的条带状组装结构, 而自由基乙基紫精出现的条带组装结构比较密集且不能稳定存在. 继续降低电极电势, 庚基紫精的吸附结构会随之出现明显的变化,而乙基紫精不会有吸附结构改变的响应.     

紫精类化合物分子聚集体材料的界面组装

紫精类化合物具有良好的电化学活性,并且在发生氧化还原反应时伴有颜色的变化,在膜修饰电极、电致变色材料和分子器件的研制等方面受到广泛的关注。紫精中的烷基链非常易于进行化学修饰,因而比较适合于通过自下而上的分子自组装技术制备多功能的分子和纳米材料。本文综述了利用Langmuir-Blodgett法、自组装法和层层组装法制备紫精分子聚集体材料的研究进展,并讨论了分子聚集体薄膜中紫精的结构、电致变色、电化学氧化还原特性及其在研制超分子器件方面的应用。     

聚紫精-脂肪酸盐表面活性剂复合物的组装合成及相行为研究

通过Menshutkin反应合成聚(对亚二甲苯基-4,4'-联吡啶二溴)(PXV)半刚性链聚紫精,采用等量混合法将聚紫精与系列不同碳链长度的阴离子表面活性剂脂肪酸钠Cn-1COONa(n=10,12,14,16,18)组装制备聚电解质-表面活性剂(PXV-Cn)复合物,运用DSC,TGA,XRD,FTIR等表征手段初步考察复合物的超分子结构及相行为.基于FTIR谱学分析特征、小角与广角变温XRD数据以及DSC热分析焓变的定量计算结果,表明半刚性主链聚紫精和脂肪酸盐极性头基组成的极性层与侧链烷烃非极性层交替排列形成层状超分子结构,其中烷烃链靠近极性端约8个亚甲基处于无定型态,其余碳链则形成结晶相.最短的PXV-C10形成少量规整度较低的三斜晶βT,n≥16以上的长碳链复合物则以六方相αH为主,其它中等长度侧链脂肪酸盐复合物则为多种结晶形式共存.随着碳链长度n的增加,侧链结晶熔点Tm升高,n≥16的长碳链复合物表现出随温度变化的可逆结晶相态变化.且这类聚紫精-表面活性剂复合物表现出高于200℃的热稳定性.     

紫精的负离子对耐水的紫精—聚合物膜的光致变色性能的影响

将含不同负离子的苄基紫精分散在混合有ＰＶＰ的ＭＭＡ－ＨＥＭＡ共聚物基质中可制成耐水的光致变色膜。它们的光致变色速度的大小随紫精负离子的不同而有如下序列：Ｖ６（ＰＦ６＾－）〉Ｖ５（ＢＦ４＾－）￣Ｖ４（ＣｌＯ４＾－）〉Ｖ３（ＣＨ３－苯环－ＳＯ３＾－）〉Ｖ２（Ｂｒ＾－）￣Ｖ１（Ｃｌ＾－）。这与这些紫精在ＤＭＦ中的溶解度以及在共聚物基质中的溶解性大小的序列相一致。负离子对这些光致变色膜在空气中的氧化退色速     

Concurrently Increasing Specific Energy and Suppressing Self-Discharge of Electrochemical Capacitors by Complexing Carbon Nanotubes with Redox Active Units-Containing Charged Copolymers

Specific energy and self-discharge are two important performances of electrochemical capacitors. In this work, we have fabricated the composite electrodes by complexing the negatively charged carboxylated multi-walled carbon nanotubes (cMWCNT) with the redox active units-containing positively charged random copolymers. 2, 2, 6, 6-Tetramethylpiperidinyl-N-oxyl and viologen are employed as model redox active units to exemplify the strategy of the concurrent increase of specific energy and suppression of self-discharge of a two-electrode device. The slower hydrogen and oxygen evolution reactions compared with the reactions of the redox active units lead to an increased electrolyte decomposition window, thereby giving rise to an increase in specific energy. On the other hand, the complexation between the cMWCNT and the copolymers suppresses both the redox shuttling and the cross-diffusion of the redox active units-containing polymer chains, leading to an improved performance of self-discharge. Based on the complexation between carbon nanotubes and redox active units-containing charged copolymers, this work provides a convenient and universal strategy to concurrently increase specific energy and suppress self-discharge of electrochemical capacitors.     

Entropy and enthalpy of polyelectrolyte complexation: Langevin dynamics simulations

We report a systematic study by Langevin dynamics simulation on the energetics of complexation between two oppositely charged polyelectrolytes of same charge density in dilute solutions of a good solvent with counterions and salt ions explicitly included. The enthalpy of polyelectrolyte complexation is quantified by comparisons of the Coulomb energy before and after complexation. The entropy of polyelectrolyte complexation is determined directly from simulations and compared with that from a mean-field lattice model explicitly accounting for counterion adsorption. At weak Coulomb interaction strengths, e.g., in solvents of high dielectric constant or with weakly charged polyelectrolytes, complexation is driven by a negative enthalpy due to electrostatic attraction between two oppositely charged chains, with counterion release entropy playing only a subsidiary role. In the strong interaction regime, complexation is driven by a large counterion release entropy and opposed by a positive enthalpy change. The addition of salt reduces the enthalpy of polyelectrolyte complexation by screening electrostatic interaction at all Coulomb interaction strengths. The counterion release entropy also decreases in the presence of salt, but the reduction only becomes significant at higher Coulomb interaction strengths. More significantly, in the range of Coulomb interaction strengths appropriate for highly charged polymers in aqueous solutions, complexation enthalpy depends weakly on salt concentration and counterion release entropy exhibits a large variation as a function of salt concentration. Our study quantitatively establishes that polyelectrolyte complexation in highly charged Coulomb systems is of entropic origin.     

Photoreduction of viologen-containing vinyl polymers by 2-propanol

In order to study the role of viologen-containing vinyl polymers in light energy conversion systems, the photoreduction of the polymer by 2-propanol and the properties of the reduced polymer were studied in comparison with methylviologen. There were marked polymer effects in the initial rate of photoreduction as well as in the absorption spectra of the photoreduced species. Both effects were interpreted in terms of the local concentration effect of viologen units in the photoreduction step. The spectral difference was found to be due to the dimeric association of the reduced viologen units on the polymer.     

Polyvalent scaffolds. Counting the number of seats available for eosin guest molecules in viologen-based host dendrimers

We have prepared and investigated two dendrimers based on a 1,3,5-trisubstituted benzenoid-type core, containing 9 and 21 viologen units in their branches, respectively, and terminated with tetraarylmethane derivatives. We have shown that, in dichloromethane solution, such highly charged cationic species give rise to strong host-guest complexes with the dianionic form of the red dye eosin. Upon complexation, the absorption spectrum of eosin becomes broader and is slightly displaced toward lower energies, whereas the strong fluorescence of eosin is completely quenched. Titration experiments based on fluorescence measurements have shown that each viologen unit in the dendrimers becomes associated with an eosin molecule, so that the number of positions ("seats") available for the guest molecules in the hosting dendrimer is clearly established, e.g., 21 for the larger of the two dendrimers. The host-guest interaction can be destroyed by addition of chloride ions, a procedure which permits eosin to escape from the dendrimer's interior in a controlled way and to regain its intense fluorescence. When chloride anions are precipitated out by addition of silver cations, eosin molecules re-enter the dendrimer's interior and their fluorescence again disappears.     

Self-assembled amorphous drug-polyelectrolyte nanoparticle complex with enhanced dissolution rate and saturation solubility

The dissolution rate and solubility of poorly soluble drugs can be enhanced by formulating them into stable amorphous nanoparticle complex (nanoplex). For this purpose, a highly sustainable self-assembly drug-polyelectrolyte complexation process is developed, with ciprofloxacin and dextran sulfate as the drug and polyelectrolyte models, respectively. The nanoplex are prepared by mixing two aqueous salt solutions - one containing the drug and the other containing the oppositely charged polyelectrolyte. The nanoplex suspension is transformed into stable dry-powder form by freeze-drying. The effects of drug concentration, drug-to-polyelectrolyte charge ratio, and salt concentration on the complexation efficiency, yield, drug loading, and nanoplex morphology are examined. The dissolution rates and solubility of the nanoplex are characterized and compared to raw drug crystals. Nearly spherical amorphous nanoplex having fairly uniform sizes in the range of 200-400 nm and 80% drug loading are successfully produced at ≥80% complexation efficiency and yield. The complexation efficiency is governed by the drug concentration and its ratio to the salt concentration. The nanoplex powders exhibit approximately twice higher dissolution rate and solubility than raw drug crystals and remain stable after one-month storage. Overall, amorphous nanoplex represent a promising bioavailability-enhanced formulation of poorly soluble drugs owed to their superior characteristics and ease of preparation.     

Self-inclusion behavior and circular dichroism of aliphatic chain-linked beta-cyclodextrin-viologen compounds and their reduced forms depending on the side of modification

[Reaction: see text]. The self-inclusion behavior and induced circular dichroism (ICD) characteristics of two beta-cyclodextrin (beta-CD) derivatives, in which a 1-methyl-4,4'-bipyridinium (viologen) group is connected by an octamethylene chain to either the primary (2(2+)) or secondary (3(2+)) side of beta-CD, and of their reduced forms, are investigated. 1H NMR studies showed that 2(2+) forms an intramolecular self-inclusion complex with K(in) = 3.1 +/- 0.4, whereas 3(2+) forms a head-to-head type of dimer with K(D) = 65 +/- 10 M(-1) at 25 degrees C. 2(2+) and 3(2+) form [2]pseudorotaxanes with alpha-CD, with the secondary side of the alpha-CD facing the viologen moiety. The ICD characteristics of mono-6-[4-(1-methyl-4-pyridinio)-1-pyridinio]-beta-CD (1(2+)), 2(2+), 3(2+), and methyloctyl viologen-beta-CD complexes were obtained for the oxidized and reduced states of the viologen units. The results indicated dimer formation for 1 degrees , and intramolecular complexation for 2*+ and 2 degrees in which the reduced viologen units are outside the beta-CD cavity. The results also indicated intramolecular complexation for 3*+ and 3 degrees, but with reduced viologen units inside the cavity. This work provides unequivocal evidence of the preference of the secondary side of cyclodextrins for viologen groups, regardless of their oxidation states, and the dependence of ICD of the viologen chromophores on their location with respect to the CD cavity.     

Fluorescence-On Response via CB7 Binding to Viologen-Dye Pseudorotaxanes

Fluorescence-on sensors typically rely on disrupting photoinduced electron transfer quenching of the excited state through binding the electron donor. To provide a more general fluorescence-on signaling unit, a quencher-fluorophore dyad has been developed in which quenching by electron transfer to a tethered viologen acceptor can be disrupted through complexation of the viologen by cucurbit[7]uril (CB7). Dyads of benzyl viologen-rhodamine B or a BODIPY fluorophore gave upon CB7 complexation 14- and 30-fold fluorescence enhancement, respectively.     

硫化镉光催化氧化二苯甲醇的反应

半导体粉能对烯烃, 芳烃等的光催化氧化, 但效率低, 揭示其机理, 研究提高催化效率是研究半导体光催化的突出问题. 本文研究了硫化镉粉末光催化氧化二苯甲醇的反应, 发现能从硫化镉导带上捕获电子的物质都能促使电荷分离, 引发或加速反应, 而自由基猝灭剂却能完全猝灭反应. 本文进一步揭示了硫化镉光催化特性并探讨了反应机理.     

Synthesis of Diazacrown Ethers with Chromophores and Their Photoinduced Charge‐Separation with Methyl Viologen

Two 4,13‐diaza‐18‐crown‐6 ethers with either two pyrenyl or two carbazolyl groups were synthesized. The two crown ethers can form complexes with methyl viologen in methanol solution. Photoirradiation of the complexes resulted in the electron transfer from the excited states of the chromophores to methyl viologen as demonstrated by the quenching of the chromophore fluorescence and the detection of the absorption spectrum of the generated viologen radical cation. The back electron transfer in these systems was inhibited by the electrostatic repulsion between the positively charged viologen radical cation and the generated chromophore radical cation. Long‐lived charge separation states (up to tens of min) were observed.     

Kinetics of formation of the host-guest complex of a viologen with cucurbit[7]uril

Host-guest complexation between the dicationic viologen 1-tri(ethylene glycol)-1'-methyl-m-xylyl-4,4'-bipyridinium and cucurbit[7]uril (CB7) was studied at pH = 4.5 in water. The stability constants of the mono- and bis-CB7 adducts were determined at 25 °C by UV-vis spectroscopy. Stopped-flow kinetic experiments were performed to measure the formation and dissociation rate constants of the monoadduct: k(1) = (6.01 ± 0.03) × 10(6) M(-1)s(-1) and k(-1) = 52.7 ± 0.4 s(-1), respectively. Possible mechanisms of complexation are discussed in view of the kinetic results.