Local Probe Oxidation of Self‐Assembled Monolayers: Templates for the Assembly of Functional Nanostructures

Surfaces with purposes : The electroinitiated patterning of self‐assembled monolayers enables the fabrication of a variety of complex nanostructures (see picture). The possibilities offered by the introduction of chemical selectivity through the local generation of chemically active groups and subsequent derivatization are reviewed, with a focus on progress in this area of research over the last four years.

     

Nanoscale Biomolecular Structures on Self‐Assembled Monolayers Generated from Modular Pegylated Disulfides

A solid‐phase synthetic strategy was developed that uses modular building blocks to prepare symmetric oligo(ethylene glycol)‐terminated disulfides with a variety of lengths and terminal functionalities. The modular disulfides, composed of alkyl amino groups linked by an amide group to oligoethylene chains were used to generate self‐assembled monolayers (SAMs), which were characterised to determine their applicability for biomolecular applications. X‐ray photoelectron spectroscopy (XPS) of the SAMs obtained from these molecules demonstrated improved stability towards displacement by 16‐hexadecanethiol, while surface plasmon resonance (SPR) analyses of SAMs prepared with the hydroxy‐terminated oligoethylene disulfide showed equal resistance to non‐specific protein adsorption in comparison to 11‐mercaptoundecyl tri(ethylene glycol). SAMs made from these adsorbates were amenable to nanoscale patterning by scanning near‐field photolithography (SNP), facilitating the fabrication of nanopatterned, protein‐functionalised surfaces. Such SAMs may be further developed for bionanotechnology applications such as the fabrication of nanoscale biological arrays and sensor devices.     

Robust Self‐Assembled Monolayers of RuII and OsII Polypyridines on Gold Surfaces: Exploring New Potentials

Functional monolayers : Ru^II and Os^II bis‐terpyridine complexes have been attached through a piperazine‐supported dithiocarbamate to a gold substrate (see picture). The robust tether, and the favourable reduction in oxidation potential induced by the electron‐rich piperazine result in self‐assembled monolayers with excellent reversible redox behaviour and exceptional stability.

     

Self‐Assembled Selenium Monolayers: From Nanotechnology to Materials Science and Adaptive Catalysis

Self‐assembled monolayers (SAMs) of selenium have emerged into a rapidly developing field of nanotechnology with several promising opportunities in materials chemistry and catalysis. Comparison between sulfur‐based self‐assembled monolayers and newly developed selenium‐based monolayers reveal outstanding complimentary features on surface chemistry and highlighted the key role of the headgroup element. Diverse structural properties and reactivity of organosulfur and organoselenium groups on the surface provide flexible frameworks to create new generations of materials and adaptive catalysts with unprecedented selectivity. Important practical utility of adaptive catalytic systems deals with development of sustainable technologies and industrial processes based on natural resources. Independent development of nanotechnology, materials science and catalysis has led to the discovery of common fundamental principles of the surface chemistry of chalcogen compounds.     

Molecular Suction Pads: Self‐Assembled Monolayers of Subphthalocyaninatoboron Complexes on Gold

Subphthalocyaninatoboron complexes with six long‐chain alkylthio substituents in their periphery are applicable for the formation of self‐assembled monolayers (SAMs) on gold. Such films are prepared from solution with the axially chlorido‐substituted derivatives and characterised by near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy, X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The results are in accord with the formation of SAMs assembled by the chemisorption of both covalently bound thiolate‐type as well as coordinatively bound thioether units. The adsorbate molecules adopt an essentially flat adsorption geometry on the substrate, resembling a suction pad on a surface.     

Modification of Electrode Surfaces by Self‐Assembled Monolayers of Thiol‐Terminated Oligo(Phenyleneethynylene)s

The wire‐like properties of four S‐(4‐{2‐[4‐(2‐phenylethynyl)phenyl]ethynyl}phenyl) thioacetate derivatives, PhC≡CC₆H₄C≡CC₆H₄SAc ( 1 ), H₂NC₆H₄C≡CC₆H₄C≡CC₆H₄SAc ( 2 ), PhC≡CC₆H₂(OMe)₂C≡CC₆H₄SAc ( 3 ) and AcSC₆H₄C≡CC₆H₄C≡CC₆H₄SAc ( 4 ) (Figure 1 ), all of which possess a high degree of conjugation along the oligo(phenyleneethynylene) (OPE) backbone, were investigated as self‐assembled monolayers (SAMs) on gold and platinum electrodes by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The redox probe [Fe(CN)₆]₄^? was used in both the CV and impedance experiments. The results indicate that the thiolates derived from thioacetate‐protected precursor molecules 1 and 2 form well‐ordered monolayers on a gold electrode, whereas SAMs derived from 3 and 4 exhibit randomly distributed pinholes. The electron tunnelling resistance and fractional coverage of SAMs of all four compounds were examined using electron tunnelling theory. The analysis of the results reveal that the well‐ordered SAMs of 1 and 2 exhibit higher charge‐transfer resistance in comparison to the defect‐ridden SAMs of 3 and 4 . The additional steric bulk offered by the methoxy groups in 3 is likely to prevent efficient packing within the SAM, leading to a microelectrode behaviour, when assembled on a gold electrode surface. The protected dithiol derivative 4 probably binds to the surface through both terminal groups which prevents dense packing and leads to the formation of a monolayer with randomly distributed pinholes. Atomic force microscopy (AFM) was used to examine the morphology of the monolayers, and height images gave root‐mean‐square (RMS) roughness′s which are in agreement with the proposed SAM structures.     

Construction of Supramolecular Self‐Assembled Microfibers with Fluorescent Properties through a Modified Ionic Self‐Assembly (ISA) Strategy

Highly ordered supramolecular microfibers were constructed through a simple ionic self‐assembly strategy from complexes of the N‐tetradecyl‐N‐methylpyrrolidinium bromide (C₁₄MPB) surface‐active ionic liquid and the small methyl orange (MO) dye molecule, with the aid of patent blue VF sodium salt. By using scanning electron microscopy and polarized optical microscopy, the width of these self‐assembled microfibers is observed to be about 1 to 5 μm and their length is from tens of micrometers to almost a millimeter. The ¹H NMR spectra of the microfibers indicates that the supramolecular complexes are composed of C₁₄MPB and MO in equal molar ratio. The electrostatic, hydrophobic, and π–π stacking interactions are regarded as the main driving forces for the formation of microfibers. Furthermore, through characterization by using confocal fluorescence microscopy, the microfibers were observed to show strong fluorescent properties and may find potential applications in many fields.     

Using Azobenzene‐Embedded Self‐Assembled Monolayers To Photochemically Control Cell Adhesion Reversibly

A celling point : A mixed self‐assembled monolayer comprising two types of alkanethiols—one containing an azobenzene unit terminated with a peptide, the other containing a hexa(ethylene glycol) group that resists nonspecific cell adhesion—enables cell adhesion to be modulated photochemically. The reversible conversion of the azobenzene moiety between E and Z configurations allows the surface to either support or resist cell adhesion.

     

Electrochemical Deposition onto Self‐Assembled Monolayers: New Insights into Micro‐ and Nanofabrication

Pattern transfer with high resolution is a frontier topic in the emerging field of nanotechnologies. Electrochemical molding is a possible route for nanopatterning metal, alloys and oxide surfaces with high resolution in a simple and inexpensive way. This method involves electrodeposition onto a conducting master covered by a self‐assembled alkanethiolate monolayer (SAMs). This molecular film enables direct surface–relief pattern transfer from the conducting master to the inner face of the electrodeposit, and also allows an easy release of the electrodeposited film due their excellent anti‐adherent properties. Replicas of the original conductive master can be also obtained by a simple two‐step procedure. SAM quality and stability under electrodeposition conditions combined with the formation of smooth electrodeposits are crucial to obtain high‐quality pattern transfer with sub‐50 nm resolution.     

Self‐Assembled Monolayers of Alkoxy‐Substituted Octadehydrodibenzo[12]annulenes on a Graphite Surface: Attempts at peri‐Benzopolyacene Formation by On‐Surface Polymerization

Self‐assembled monolayers of a series of tetraalkoxy‐substituted octadehydrodibenzo[12]annulene (DBA) derivatives 1 c – g possessing butadiyne linkages were studied at the 1,2,4‐trichlorobenzene (TCB) or 1‐phenyloctane/graphite interface by scanning tunneling microscopy (STM). The purpose of this research is not only to investigate the structural variation of two‐dimensional (2D) monolayers, but also to assess a possibility for peri‐benzopolyacene formation by two‐dimensionally controlled polymerization on a surface. As a result, the formation of three structures, porous, linear, and lamella structures, were observed by changing the alkyl chain length and the solute concentration. The formation of multilayers of the lamella structure was often observed for all compounds. The selection of molecular networks is basically ascribed to intermolecular and molecule–substrate interactions per unit area and network density. The selective appearance of the linear structure of 1 d is attributed to favorable epitaxial registry matching between the substrate lattice and the overlayer lattice. Even though the closest interatomic distance between the diacetylenic units of the DBAs in the lamella structure (≈0.6 nm) is slightly larger compared to the typical distances necessary for topochemical polymerization, the reactivity toward external stimuli (electronic‐pulse irradiation from an STM tip and UV irradiation) was investigated. Unfortunately, no evidence for polymerization of the DBAs on the surface was observed. The present results indicate the necessity for further designing a suitable system for the on‐surface construction of structurally novel conjugated polymers, which are otherwise difficult to prepare.