Oligothiophene Assemblies Defined by DNA Interaction: From Single Chains to Disordered Clusters

The organization of conjugated polyelectrolytes (CPEs) interacting with biomolecules sets conditions for the biodetection of biological processes and identity, through the use of optical emission from the CPE. Herein, a well‐defined CPE and its binding to DNA is studied. By using dynamic light scattering and circular dichroism spectroscopy, it is shown that the CPE forms a multimolecule ensemble in aqueous solution that is more than doubled in size when interacting with a small DNA chain, while single chains are evident in ethanol. The related changes in the fluorescence spectra upon polymer aggregation are assigned to oscillator strength redistribution between vibronic transitions in weakly coupled H‐aggregates. An enhanced single‐molecule spectroscopy technique that allows full control of excitation and emission light polarization is applied to combed and decorated λDNA chains. It is found that the organization of combed CPE–λDNA complexes (when dry on the surface) allows considerable variation of CPE distances and direction relative to the DNA chain. By analysis of the polarization data energy transfer between the polymer chains in individual complexes is confirmed and their sizes estimated.     

Cyclodextrin Insulation Prevents Static Quenching of Conjugated Polymer Fluorescence at the Single Molecule Level

Conjugated polymers (CPs) are promising materials for fluorescence imaging application. However, a significant problem in this field is the unexplained abnormally low fluorescence brightness (or number of fluorescence photons detected per one excitation photon) exhibited by most of CP single chains in solid polymer hosts. Here it is shown that this detrimental effect can be fully avoided for short chains of polyfluorene‐bis‐vinylphenylene (PFBV) embedded in a host polymer matrix of PMMA, if the conjugated backbone is insulated by cyclodextrin rings to form a polyrotaxane (PFBV‐Rtx). Fluorescence kinetics and quantum yields are measured for the polymers in liquid solutions, pristine films, and solid PMMA blends. The fluorescence brightness of PFBV‐Rtx single chains dispersed in a solid PMMA is very close to that expected for a chain with 100% fluorescence quantum yield, while the unprotected PFBV chains of the same length possess 4 times lower brightness. Despite this, the fluorescence decay kinetics are the same for both polymers, suggesting the presence of static or ultrafast fluorescence quenching in the unprotected polymer. About 80% of an unprotected PFBV chain is estimated to be completely quenched. The hypothesis is that the cyclodextrin rings prevent the quenching by working as ‘bumpers’ reducing the mechanical forces applied by the host polymer to the conjugated backbone and help retaining its conformational freedom. While providing a recipe for making CP fluorescence bright at the single‐molecule level, these results identify a lack of fundamental understanding in the community of the influence of the environment on excited states in conjugated materials.     

Emission Tuning with Size‐Controllable Polymer Dots from a Single Conjugated Polymer

Two conjugated polymers (CPs) with various compositions of phenylene and benzoselenadiazoben (BSD) are synthesized to have a special emitting property; different fluorescence colors in solution and in the solid states, allowing the resulting conjugated polymer dots (Pdots) to emit different fluorescence colors upon their size variation. The photophysical property of such different‐sized Pdots is investigated using fluorescence spectra and fluorescence lifetimes. A decrease in the fluorescence lifetime of Pdots is observed with an increase in the size of Pdots, caused by quantitative change in energy transfer from phenylene (energy donor) to the BSD unit (energy acceptor). The results provide that any CP can be used for the fabrication of Pdots with size‐tunable emission, as long as the CP shows different emissions according to its phases. Such emission of Pdots can even be observed when in the solid solution in polymer matrix, which emits different fluorescence colors depending on the size of embedded Pdots in the polymer matrix.     

Plasmon Resonance Energy Transfer: Coupling between Chromophore Molecules and Metallic Nanoparticles

Plasmon resonance energy transfer (PRET) from a single metallic nanoparticle to the molecules adsorbed on its surface has attracted more and more attentions in recent years. Here, a molecular beacon (MB)‐regulated PRET coupling system composed of gold nanoparticles (GNPs) and chromophore molecules has been designed to study the influence of PRET effect on the scattering spectra of GNPs. In this system, the chromophore molecules are tagged to the 5′‐end of MB, which can form a hairpin structure and modified on the surface of GNPs by its thiol‐labeled 3′‐end. Therefore, the distance between GNPs and chromophore molecules can be adjusted through the open and close of the MB loop. From the peak shift, the PRET interactions of different GNPs‐chromophore molecules coupling pairs have been calculated by discrete dipole approximation and the fitting results match well with the experimental data. Therefore, the proposed system has been successfully applied for the analysis of PRET situation between various metallic nanoparticles and chromophore molecules, and provides a useful tool for the potential application in screening the PRET‐based nanoplasmonic sensors.     

Single‐Molecule Spectroscopy for Plastic Electronics: Materials Analysis from the Bottom‐Up

π‐conjugated polymers find a range of applications in electronic devices. These materials are generally highly disordered in terms of chain length and chain conformation, besides being influenced by a variety of chemical and physical defects. Although this characteristic can be of benefit in certain device applications, disorder severely complicates materials analysis. Accurate analytical techniques are, however, crucial to optimising synthetic procedures and assessing overall material purity. Fortunately, single‐molecule spectroscopic techniques have emerged as an unlikely but uniquely powerful approach to unraveling intrinsic material properties from the bottom up. Building on the success of such techniques in the life sciences, single‐molecule spectroscopy is finding increasing applicability in materials science, effectively enabling the dissection of the bulk down to the level of the individual molecular constituent. This article reviews recent progress in single molecule spectroscopy of conjugated polymers as used in organic electronics.     

单电子转移活性自由基聚合法制备星形丙烯酰胺二元共聚物

以四氯化碳(CCl_4)为引发剂,Cu0粉/三(2-二甲氨基乙基)胺(Me6-TREN)为催化体系,在水溶液中实现了丙烯酸钠(Na AA)和丙烯酰胺(AM)的单电子转移活性自由基聚合(SET-LRP),得星形二元共聚物P(AM-co-AA)。考察了引发剂用量、催化剂用量、失活剂用量及引发温度和反应物浓度对Star shaped-P(AM-co-AA)黏均分子量的影响。结果表明,当引发温度为25.0℃,物料摩尔比为单体∶Me6-TERN∶CCl_4∶Cu Cl_2∶Cu0=680∶0.75∶1.25∶0.35∶0.7(其中,m(AM)∶m(Na AA)=4∶1)时,即AM在溶液中的质量分数为17.5%,Na AA在溶液中的质量分数为7.5%,引发剂在溶液中的质量分数为0.105%,催化剂在溶液中的质量分数为0.0224%,失活剂在溶液中的质量分数为0.024%时,所得聚合物产品相对分子质量最高,达到331万。     

岩石变形破坏过程中的能量传递和耗散研究

岩石变形破坏的过程是和外界产生能量交换的过程。从理论上分析了用能量方法研究岩石破坏问题的合理性,以及岩石在变形过程中弹性能、塑性能、表面能、辐射能、动能之间相互转化的过程、计算原理、以及对岩石破坏所起的不同作用。并分别从宏观和微观的角度研究了在不同的变形阶段中岩石能量耗散与释放问题。在宏观上,岩石变形前期以弹性应变能的方式存储外界提供的能量,同时又通过损伤演化等向外界耗散能量;变形的后期以剧烈的能量释放为主。微观上,存在多种引起岩石应变硬化和应变软化的机制,岩石存储能量还是向外界释放能量取决于这些微观机制竞争的最后结果,基于此推导了岩石变形中能量的传递方程,用试验研究了能量的转化和平衡,以及耗散能和释放能之间的比例关系。结果表明能量耗散导致岩石强度的降低,而能量释放是造成岩石灾变破坏的真正原因。从能量耗散与释放的观点研究岩石的破坏,可以从本质上把握岩石变形和破坏的物理机理,寻找岩石破坏的真正原因,为实际工程提供参考。     

Fluorescence Anisotropy Reloaded—Emerging Polarization Microscopy Methods for Assessing Chromophores' Organization and Excitation Energy Transfer in Single Molecules,Particles, Films,and Beyond

Fluorescence polarization is widely used to assess the orientation/rotation of molecules, and the excitation energy transfer between closely located chromophores. Emerging since the 1990s, single molecule fluorescence spectroscopy and imaging stimulate the application of light polarization for studying molecular organization and energy transfer beyond ensemble averaging. Here, traditional fluorescence polarization and linear dichroism methods used for bulk samples are compared with techniques specially developed for, or inspired by, single molecule fluorescence spectroscopy. Techniques for assessing energy transfer in anisotropic samples, where the traditional fluorescence anisotropy framework is not readily applicable, are discussed in depth. It is shown that the concept of a polarization portrait and the single funnel approximation can lay the foundation for alternative energy transfer metrics. Examples ranging from fundamental studies of photoactive materials (conjugated polymers, light‐harvesting aggregates, and perovskite semiconductors) to Förster resonant energy transfer (FRET)‐based biomedical imaging are presented. Furthermore, novel uses of light polarization for super‐resolution optical imaging are mentioned as well as strategies for avoiding artifacts in polarization microscopy.     

Y2O2S:0.03Eu,0.03Ti的长余辉特性及Ti向Eu3+的余辉传能机制

采用高温还原法合成了Eu，Ti共激活橙红色Y2O2S长余辉发光材料，并测量了Y2O2S：0．03Eu,0．03Ti磷光体的荧光光谱，余辉分辨和余辉衰减曲线谱．实验结果表明，Y2O2S：0．03Eu,0．03Ti磷光体的发射谱由一系列Eu^3＋离子内部能级跃迁的尖峰组成；余辉分辨谱则不同，由一个主峰位于565nm的宽发射带和一系列波长范围位于500nm以上的窄发射带两种峰形组成，可分别归为Ti离子的宽带余辉发射和三价Eu^3＋的线状余辉发射,分析认为，样品中存在Ti余辉发射向Eu^3＋内部能级间产生选择性的余辉传能机制，从而导致Y2O2S：0．03Ti，0．03Eu磷光体中同时出现两种发光中心离子的余辉分辨谱现象．     

Approaching Intra‐ and Interchain Charge Transport of Conjugated Polymers Facilely by Topochemical Polymerized Single Crystals

Charge transport of small molecules is measured well with scanning tunneling microscopy, conducting atomic force microscopy, break junction, nanopore, and covalently bridging gaps. However, the manipulation and measurement of polymer chains remain a long‐standing fundamental issue in conjugated polymers and full of challenge since conjugated polymers are naturally disordered materials. Here, a fundamental breakthrough in generating high‐quality conjugated‐polymer nanocrystals with extended conjugation and exceptionally high degrees of order using a surface‐supported topochemical polymerization method is demonstrated. In the crystal the conjugated‐polymer chains are extended along the long axis of the crystal with the side chains perpendicular to the long axis. Devices with conducting channels along the polymer chains show efficient charge transport, nearly two orders of magnitude greater than the interchain charge transport along the π–π stacking direction. This is the first example to clarify intra‐ and interchain charge transport based on an individual single crystal of conjugated polymers, and demonstrate the importance of intrachain charge transport in plastic electronics.     

有机电致发光材料的能隙计算

有机电致发光材料具有可进行分子结构设计而改变其溶解性及光电性能等特点,以此为功能层、将电能转换为光能的有机电致发光二极管更是具备轻薄、高效、自发光、低能耗以及低成本可实现柔性器件等潜在优势。因此,研究合成高性能的有机电致发光材料并应用于制备可实用化的显示器及照明产品成了业界研究的热点。文中综述了以能带理论为基础,对有机电致发光材料进行结构设计改进发光性能时对将合成的材料的能隙计算的理论模型与计算方法及其应用进展,可望为聚合物发光材料的合成设计提供理论支持。     

Direct Manipulation of a Single Potassium Channel Gate with an Atomic Force Microscope Probe

Ion channels are membrane proteins that regulate cell functions by controlling the ion permeability of cell membranes. An ion channel contains an ion‐selective pore that permeates ions and a sensor that senses a specific stimulus such as ligand binding to regulate the permeability. The detailed molecular mechanisms of this regulation, or gating, are unknown. Gating is thought to occur from conformational changes in the sensor domain in response to the stimulus, which results in opening the gate to permit ion conduction. Using an atomic force microscope and artificial bilayer system, a mechanical stimulus is applied to a potassium channel, and its gating is monitored in real time. The channel‐open probability increases greatly when pushing the cytoplasmic domain toward the membrane. This result shows that a mechanical stimulus at the cytoplasmic domain causes changes in the gating and is the first to show direct evidence of coupling between conformational changes in the cytoplasmic domain and channel gating. This novel technology has the potential to be a powerful tool for investigating the activation dynamics in channel proteins.