星形低分子量块状化合物的合成

近来对由不相容部分构成的块状共聚物的研究表明,通过改变各块的对比度(刚性与柔性,亲水性与亲油性,极性与非极性等)或改变各块的相对体积比, 均可改变这类物质的自组装行为获得新的液晶相态[1a].     

Gold Nanoparticles Stabilized by Single Tripodal Ligands

In order to coat the entire surface of gold nanoparticles (AuNPs) by a single ligand, tripodal macromolecules comprising benzylic thioethers coordinating to the AuNP surface are synthesized and their abilities to stabilize AuNPs are investigated. Out of the five studied ligands 1 – 5 , the tetraphenylmethane‐based oligomers 4 and 5 display excellent AuNP coating features. Both ligand structures are able to control the dimensions of the AuNPs by stabilizing particles of narrow size distributions during their syntheses (1.05 ± 0.28 nm for Au‐4 , and 1.15 ± 0.34 nm for Au‐5 ). Closer inspection of these AuNPs by transmission electron microscopy and thermogravimetric analyses suggests that single ligands 4 and 5 are able to stabilize entire AuNPs. These particles Au‐4 and Au‐5 are obtained in good yields and display promising thermal stabilities (110 °C for Au‐4 , and 95 °C for Au‐5 ), making them interesting nanoscale inorganic–organic building blocks for further functionalization/processing by wet chemistry.     

Linear Tetraphenylmethane‐Based Thioether Oligomers Stabilising an Entire Gold Nanoparticle by Enwrapping

The design and synthesis of a novel linear thioether‐based ligand subunit with a tetraphenylmethane core used in the stabilisation of gold nanoparticles (AuNPs) are presented. Mono‐, tri, penta‐ and heptamers of the ligand have been synthesised and used to stabilise AuNPs by enwrapping. With the exception of the monomer, all ligands provide reliable long‐term stability and redispersibility for the coated nanoparticles in common organic solvents. Despite variation of the oligomer length, all stable particles were of the same size within error tolerance (1.16±0.32 nm for the trimer, 1.15±0.30 nm for the pentamer, 1.17±0.34 nm for the heptamer), as investigated by transmission electron microscopy (TEM). These findings suggest that not only the number of sulfur atoms in the ligand, but also its bulkiness play a crucial role in stabilising the AuNPs. These findings are supported by thermogravimetric analysis (TGA), showing that AuNPs stabilised by the penta‐ or heptamer are passivated by a single ligand. Thermal stability measurements suggest a correlation between ligand coverage and thermal stability, further supporting these findings.     

Importance of the Anchor Group Position (Para versus Meta) in Tetraphenylmethane Tripods: Synthesis and Self‐Assembly Features

The efficient synthesis of tripodal platforms based on tetraphenylmethane with three acetyl‐protected thiol groups in either meta or para positions relative to the central sp³ carbon for deposition on Au (111) surfaces is reported. These platforms are intended to provide a vertical arrangement of the substituent in position 4 of the perpendicular phenyl ring and an electronic coupling to the gold substrate. The self‐assembly features of both derivatives are analyzed on Au (111) surfaces by low‐temperature ultra‐high‐vacuum STM, high‐resolution X‐ray photoelectron spectroscopy, near‐edge X‐ray absorption fine structure spectroscopy, and reductive voltammetric desorption studies. These experiments indicated that the meta derivative forms a well‐ordered monolayer, with most of the anchoring groups bound to the surface, whereas the para derivative forms a multilayer film with physically adsorbed adlayers on the chemisorbed para monolayer. Single‐molecule conductance values for both tripodal platforms are obtained through an STM break junction experiment.