Steering On-Surface Supramolecular Nanostructures by <i>tert</i>-Butyl Group

Molecular self-assembly is an efficient approach to fabricate supramolecular nanostructures on well-defined surfaces. The nanostructures can be regulated through functionalizing the molecular precursors with different functional groups. Here, from an interplay of high-resolution scanning tunneling microscopy imaging and density functional theory calculations, we have at the atomic scale investigated the influence of <i>tert</i>-butyl groups on the on-surface self-assembled behaviors of the organic molecules where intermolecular interactions mainly originate from relatively weak van der Waals interactions. Our results demonstrate that the <i>tert</i>-butyl groups can not only affect the adsorption geometry but also change the self-assembled properties of organic molecules on surfaces due to the enhanced intermolecular interactions

On-Surface Construction of Network Structures by the <i>tert</i>-Butyl-Substituted Organic Molecules

On-surface formation of two-dimensional supramolecular network structures using molecular self-assembly has been an efficient and the most widely employed method. Through delicate modifying the molecular candidates with specific substituents, it is possible to build on-surface nanostructures according to one’s will. Here, from the interplay of high-resolution STM imaging and DFT calculations we have investigated role of the <i>tert</i>-butyl substituent in the formation of self-assembled network structures by planar aromatic molecules on metal surfaces. Our results demonstrate that the <i>tert</i>-butyl groups can change adsorption geometry of molecule from entirely flat-lying to a bit of upright-standing and vary the intermolecular interactions, which resulted in the formation of two-dimensional supramolecular network structures on both Au(111) and Ag(110). These findings further present that <i>tert</i>-butyl substituent could be a good candidate for fabricating on-surface self-assembled nanostructures from more general aromatic molecules

Exploring the Self-Assembly Behaviors of an Organic Molecule Functionalized by Terminal Alkyne and Aldehyde Groups on Au(111)

On-surface self-assembly from molecular building blocks directed by supramolecular interactions has been widely reckoned as an efficient method for controllable construction of low-dimensional nanostructures and nanomaterials. Numerous efforts have been devoted to exploring the self-assembled behaviors of molecular precursors on different surfaces and unravelling the underlying mechanism. Generally, the molecular precursors are functionalized with one kind of functional groups for directing the self-assembly. In this study, by combining real-space direct visualization and DFT calculations, we have investigated the self-assembly behaviors of an organic molecule functionalized by two different functional groups: terminal alkyne and aldehyde groups on Au(111). An ordered racemic island nanostructure is formed on Au(111), which results from the hybrid interactions between the two functional groups. Detailed DFT calculations have been performed to compare the different binding ways and binding strengths between the organic molecules

Atomic-Scale Insight into Tautomeric Recognition, Separation, and Interconversion of Guanine Molecular Networks on Au(111)

Although tautomerization may directly affect the chemical or biological properties of molecules, real-space investigation on the tautomeric behaviors of organic molecules in a larger area of molecular networks has been scarcely reported. In this paper, we choose guanine (G) molecule as a model system. From the interplay of high-resolution scanning tunneling microscopy (STM) imaging and density functional theory (DFT) calculations, we have successfully achieved the tautomeric recognition, separation, and interconversion of G molecular networks (formed by two tautomeric forms G/9H and G/7H) with the aid of NaCl on the Au(111) surface in ultrahigh vacuum (UHV) conditions. Our results may serve as a prototypical system to provide important insights into tautomerization related issues, which should be intriguing to biochemistry, pharmaceutics, and other related fields

Atomic-Scale Investigation on the Facilitation and Inhibition of Guanine Tautomerization at Au(111) Surface

Nucleobase tautomerization might induce mismatch of base pairing. Metals, involved in many important biophysical processes, have been theoretically proven to be capable of affecting tautomeric equilibria and stabilities of different nucleobase tautomers. However, direct real-space evidence on demonstrating different nucleobase tautomers and further revealing the effect of metals on their tautomerization at surfaces has not been reported to date. From the interplay of high-resolution STM imaging and DFT calculations, we show for the first time that tautomerization of guanine from G/9H to G/7H is facilitated on Au(111) by heating, whereas such tautomerization process is effectively inhibited by introducing Ni atoms due to its preferential coordination at the N7 site of G/9H. These findings may help to elucidate possible influence of metals on nucleobase tautomerization and provide from a molecular level some theoretical basis on metal-based drug design

On-Surface Formation of One-Dimensional Polyphenylene through Bergman Cyclization

On-surface fabrication of covalently interlinked conjugated nanostructures has attracted significant attention, mainly because of the high stability and efficient electron transport ability of these structures. Here, from the interplay of scanning tunneling microscopy imaging and density functional theory calculations, we report for the first time on-surface formation of one-dimensional polyphenylene chains through Bergman cyclization followed by radical polymerization on Cu(110). The formed surface nanostructures were further corroborated by the results for the ex situ-synthesized molecular product after Bergman cyclization. These findings are of particular interest and importance for the construction of molecular electronic nanodevices on surfaces

Formation of a G‑Quartet-Fe Complex and Modulation of Electronic and Magnetic Properties of the Fe Center

Although the G-quartet structure has been extensively investigated due to its biological importance, the formation mechanism, in particular, the necessity of metal centers, of an isolated G-quartet on solid surfaces remains ambiguous. Here, by using scanning tunneling microscopy under well-controlled ultra-high-vacuum conditions and density functional theory calculations we have been able to clarify that besides the intraquartet hydrogen bonding a metal center is mandatory for the formation of an isolated G-quartet. Furthermore, by subtly perturbing the local coordination bonding schemes within the formed G-quartet complex <i>via</i> local nanoscale scanning tunneling microscopy manipulations, we succeed in modulating the d orbitals and the accompanying magnetic properties of the metal center. Our results demonstrate the feasibility of forming an isolated G-quartet complex on a solid surface and that the strategy of modulating electronic and magnetic properties of the metal center can be extended to other related systems such as molecular spintronics