Self-Assembled Graphene/MWCNT Bilayers as Platinum-Free Counter Electrode in Dye-Sensitized Solar Cells

We describe the preparation and properties of bilayers of graphene- and multi-walled carbon nanotubes (MWCNTs) as an alternative to conventionally used platinum-based counter electrode for dye-sensitized solar cells (DSSC). The counter electrodes were prepared by a simple and easy-to-implement double self-assembly process. The preparation allows for controlling the surface roughness of electrode in a layer-by-layer deposition. Annealing under N₂ atmosphere improves the electrode's conductivity and the catalytic activity of graphene and MWCNTs to reduce the I₃⁻ species within the electrolyte of the DSSC. The performance of different counter-electrodes is compared for ZnO photoanode-based DSSCs. Bilayer electrodes show higher power conversion efficiencies than monolayer graphene electrodes or monolayer MWCNTs electrodes. The bilayer graphene (bottom)/MWCNTs (top) counter electrode-based DSSC exhibits a maximum power conversion efficiency of 4.1 % exceeding the efficiency of a reference DSSC with a thin film platinum counter electrode (efficiency of 3.4 %). In addition, the double self-assembled counter electrodes are mechanically stable, which enables their recycling for DSSCs fabrication without significant loss of the solar cell performance.     

Structural Transformation of 2,7-Dibromopyrene on Au(111) Mediated by Halogen-Bonding Motifs

Fundamental understanding of the bonding motifs that elaborately mediate the formation of supramolecular nanostructures is essential for the rational design of stable artificial organic architectures. Herein, the structural transformation of the adsorption complex of 2, 7-dibromopyrene (Br₂Py) on the Au(111) surface has been investigated by scanning tunnelling microscopy combined with X-ray photoemission spectroscopy and density function theory calculations. In the initial stage of self-assembly, well ordered patterns are formed in the manner of extended supramolecular structures balanced by intermolecular halogen bonding motifs, whilst the Au(111) reconstruction is still fairly visible. Subsequent thermal annealing promotes the dehalogenation and on-surface Ullmann coupling, and polymerized oligomers are consequently constructed. Interestingly, such polymerized chains are still stably mediated by the halogen bonding motif via dissociated Br atoms which are revealed to be absorbed on the bridge site of Au(111), while the number of halogen bonds increases significantly from self-assembly to Ullmann coupling polymerization, indicating that the halogen bonding motif contributes significantly to the extended one-dimensional polymers.     

Development of new amphiphilic bio-organic assemblies for potential applications in iron-binding and targeting tumor cells

Iron overload has been implicated in the pathogenesis of many neurodegenerative diseases, cancer and thalassemia. In this work, we have developed new supramolecular assemblies as potential iron chelators for mitigating iron overload at the cellular level. We utilized fluorenyl-based building blocks that were functionalized with ethylene diamine (Fmoc-Ed) or arginine (Fmoc-Arg). Fmoc-Ed was further conjugated with ureido propionic acid (UDP) or pyrazole-3-carboxylic acid (PCA). Each of the building blocks were self-assembled into nanovesicles or fibers and further functionalized with the transferrin receptor binding peptide THRPPMWSPVWP (Tf) to promote receptor mediated cellular uptake. Our results indicated that the assemblies were able to target HeLa cells, induce apoptosis, ROS formation and were able to penetrate the cells. The degree of cellular impact was dependent upon the structure of the assemblies. The effects were more prominent under iron overload conditions compared to normal growth conditions. Our results suggest that such nanoscale assemblies may open new avenues for further studies into iron chelation and mitigation of iron overload using Fmoc-functionalized building blocks.     

3‐[4′‐(Diethylboryl)phenyl]pyridine: Exclusive Crystallization of the Cyclic Tetramer

The crystallization of 3‐[4′‐(diethylboryl)phenyl]pyridine ( 1 ), which formed a mixture of oligomers in solution with the cyclic trimer as a major component, in acetone at 0 °C afforded a cyclic tetramer that co‐crystallized with solvent molecules. Similarly, solutions of compound 1 in toluene at 10 °C and in benzene at 8 °C furnished the cyclic tetramer with the incorporation of toluene and benzene molecules, respectively, thus suggesting that the cyclic tetramer was the minor component. ¹³C CP/MAS NMR spectroscopy of precipitates of compound 1 suggested that precipitation from acetone and toluene each afforded mixtures of the cyclic trimer and the cyclic tetramer, whereas precipitation from benzene exclusively furnished the cyclic tetramer. Therefore, it appeared that crystallization readily shifted the equilibrium towards the cyclic tetramer in benzene. The thermodynamic parameters for the equilibrium between these two oligomers in [D₆]benzene, as determined from a van′t Hoff plot, were ΔH°=?8.8 kcal mol^?1 and ΔS°=?23.7 cal mol^?1 K^?1, which were coincident with previously reported calculations and observations.     

Self‐Assembly of Aggregation‐Induced‐Emission Molecules

The last decade has witnessed rapid developments in aggregation‐induced emission (AIE). In contrast to traditional aggregation, which causes luminescence quenching (ACQ), AIE is a reverse phenomenon that allows robust luminescence to be retained in aggregated and solid states. This makes it possible to fabricate various highly efficient luminescent materials, which opens new paradigms in a number of fields, such as imaging, sensing, medical therapy, light harvesting, light‐emitting devices, and organic electronic devices. Of the various important features of AIE molecules, their self‐assembly behavior is very attractive because the formation of a well‐defined emissive nanostructure may lead to advanced applications in diverse fields. However, due to the nonplanar topology of AIEgens, it is not easy for them to self‐assemble into well‐defined structures. To date, some strategies have been proposed to achieve the self‐assembly of AIEgens. Herein, we summarize the most recent approaches for the self‐assembly of AIE molecules. These approaches can be sorted into two classes: 1) covalent molecular design and 2) noncovalent supramolecular interactions. We hope this will inspire more excellent work in the field of AIE.     

Interfacial Self‐Assembly of Closely Packed Nanoparticle Arrays of Silica@Multiporphyrin Hybrids as Light‐Sensitizers for Dye Degradation and Viologen Photochromism

Light‐sensitizer functionalized organic–inorganic hybrid materials have attracted much attention owing to their potential applications in the fields of optoelectronics, heterogeneous catalysis, sensors, and nanotechnology. Here, an interfacial self‐assembly of zero‐dimensional (0D) silica@multiporphyrin array nanohybrids and their 3D Langmuir–Blodgett (LB) films is reported. Photoactive tetrapyridylporphyrin (TPyP) was first assembled on the silica nanoparticles’ surfaces via silane, substitution, and coordination reactions to produce nanoSiO₂@(Pd‐TPyP)_n hybrids. Then, the Cd²⁺‐nanoSiO₂@(Pd‐TPyP)_n monolayers and LB films were constructed on the CdCl₂ subphase surface. These monolayers and LB films displayed stronger stability, as well as more uniform and closely packed nanoparticle arrays compared with those prepared on the pure water surface, owing to the formation of strong network‐like Pd‐ and Cd‐TPyP coordination units, which significantly enhanced the nanoparticles’ interaction. Further, compared with that of the 0D nanoSiO₂@(Pd‐TPyP)_n hybrids, the degradation efficiency was nearly 20 times higher when the hybrids’ LB films were used as light‐sensitizers for the photocatalytic degradation of RhB. Finally, flexible photochromic devices were constructed by using the LB films sandwiched between two electrodes, which displayed a reversible photoinduced redox reaction of viologen together with a color change process. Because TPyP was strongly immobilized on the nanoparticles’ surfaces and the particles were connected through the Py‐Pd²⁺‐Py and Py‐Cd²⁺‐Py coordination units with the 3D network‐like architecture, the present nanohybrids and LB films had good stability and reusability.     

三明治结构纳米银/氧化石墨烯基底的制备及SERS性能

采用易操作且低成本的静电自组装方法, 在质子化的玻璃基片上, 通过交替沉积氧化石墨烯(GO) 和带正电荷的银纳米粒子(AgNPs) 获得少数层GO和AgNPs复合薄膜(AgNPs/GO). 采用紫外-可见光吸收光谱、 原子力显微镜和扫描电子显微镜对复合薄膜的生长和表面形貌进行了表征. 结果表明, 通过调控AgNPs 溶胶浓度和自组装循环次数, 可以获得AgNPs/GO/AgNPs 的三明治结构, 并在基底表面形成均匀的AgNPs 聚集体. 表面增强拉曼散射(SERS)研究结果表明, AgNPs/GO-4基底具有最佳的SERS性能, 其对罗丹明6G(R6G) 和结晶紫的平均拉曼增强因子分别为3.4×10⁸和1.3×10⁹, 对R6G的最低检测浓度约为10^-12 mol/L. 多层三明治结构和较小颗粒间距使得AgNPs层之间产生强烈的耦合作用, 并在GO片层间产生大量的“热点”, 显著提高SERS性能, 而少数层GO具有强吸附性, 有利于分子在基底中富集, 从而起到化学增强作用, 提高SERS灵敏度.     

Controlled Growth of Porphyrin Wires at a Solid‐Liquid Interface

Bis(zinc porphyrin) scaffolds bearing C₈ or C₁₈ alkyl chains and imidazole end groups self‐assembled in a head‐to‐tail fashion into multi‐porphyrin assemblies on both HOPG and mica. Due to weaker molecule surface‐interactions, longer arrays formed on mica than on HOPG. In both cases, it was essential first to generate monomers that were drop casted on the surface, then to allow time for the bis(zinc porphyrins) to assemble. Although thicker fibrous assemblies were observed with the C₈ alkyl substituents than with the longer chains, noncovalent assemblies up to 1 μm long were observed for each molecule. These investigations provide a reproducible, noncovalent method to grow porphyrin arrays that may be of interest in molecular electronics for charge transport.     

石墨烯迷你马达的自组装制备及其乙醇驱动运动和油品吸附性能

石墨烯三维(3D)宏观体多集中在厘米尺度并为实心对称结构,且存在“小尺寸”和“低密度”难以协调的矛盾。 本文以氧化石墨烯为前驱体、苯胺为交联剂,在电动搅拌下通过剪切力驱动聚集和毛细管力干燥协同自组装制备球状氧化石墨烯水凝胶,经过高温还原得到石墨烯迷你马达。 所得石墨烯迷你马达具有尺寸小(直径2~5 mm)、密度低(0.2~0.7 g/cm³)、内部空心结构以及疏水亲油的性能。 上述结构特征赋予其乙醇驱动运动和油品吸附性能。 研究表明,充分浸泡乙醇的石墨烯迷你马达在水中可以展现出自转速度3 r/s的无规则快速运动;对水中植物油的饱和吸附量约为794.9 mg/g。     

一个强荧光三维超分子有机框架的构建及其对苦味酸的选择性传感

在四苯基甲烷外侧通过C=C双键引入四个N-甲基-4-苯基吡啶盐片段,合成了一个新的全共轭单体T-1.其在水中与2 equiv.的葫芦脲[8]结合,形成了新的高强荧光的超分子有机框架SOF-r-SPP.动态光散射实验表明,在T-1浓度为1.0和0.031 mmol/L时,SOF-r-SPP的流体力学直径分别为68和41 nm.粉末X-射线衍射实验揭示,SOF-r-SPP形成孔径为2.3 nm的三维金刚石型周期性结构.硝基苯衍生物能有效淬灭SOF-r-SPP的荧光.在17个研究的硝基苯类分子中,苦味酸的淬灭效率最高. SOF-r-SPP作为荧光传感器,对苦味酸的检测极限可以达到0.024 mmol/L.