Molecular Self-Assembly and Adsorption Structure of 2,2'-Dipyrimidyl Disulfides on Au(111) Surfaces.

The effects of solution concentration and pH on the formation and surface structure of 2-pyrimidinethiolate (2PymS) self-assembled monolayers (SAMs) on Au(111) via the adsorption of 2,2'-dipyrimidyl disulfide (DPymDS) were examined using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM observations revealed that the formation and structural order of 2PymS SAMs were markedly influenced by the solution concentration and pH. 2PymS SAMs formed in a 0.

ZnO/Graphene Oxide on Halloysite Nanotubes as a Superabsorbent Nanocomposite Photocatalyst for the Degradation of Organic Dyes.

Using renewable photocatalysts for pollutant degradation represents a promising approach to addressing environmental water challenges by harnessing solar energy without additional energy consumption. However, for the practical use of photocatalysts, it is necessary to improve catalyst efficiency, considering cost and biocompatibility. In this study, we developed a new superabsorbent photocatalyst for the degradation of organic dyes in water.

Formation and Thermal Stability of Ordered Self-Assembled Monolayers by the Adsorption of Amide-Containing Alkanethiols on Au(111).

We examined the surface structure, binding conditions, electrochemical behavior, and thermal stability of self-assembled monolayers (SAMs) on Au(111) formed by -(2-mercaptoethyl)heptanamide (MEHA) containing an amide group in an inner alkyl chain using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) to understand the effects of an internal amide group as a function of deposition time. The STM study clearly showed that the structural transitions of MEHA SAMs on Au(111) occurred from the liquid phase to the formation of a closely packed and well-ordered β-phase via a loosely packed α-phase as an intermediate phase, depending on the deposition time. XPS measurements showed that the relative peak intensities of chemisorbed sulfur against Au 4f for MEHA SAMs formed after deposition for 1 min, 10 min, and 1 h were calculated to be 0.

Thermally Driven Structural Order of Oligo(Ethylene Glycol)-Terminated Alkanethiol Monolayers on Au(111) Prepared by Vapor Deposition.

To probe the effects of deposition temperature on the formation and structural order of self-assembled monolayers (SAMs) on Au(111) prepared by vapor deposition of 2-(2-methoxyethoxy)ethanethiol (CHO(CH)O(CH)SH, EG2) for 24 h, we examined the surface structure and electrochemical behavior of the resulting EG2 SAMs using scanning tunneling microscopy (STM) and cyclic voltammetry (CV). STM observations clearly revealed that EG2 SAMs vapor-deposited on Au(111) at 298 K were composed of a disordered phase on the entire Au surface, whereas those formed at 323 K showed improved structural order, showing a mixed phase of ordered and disordered phases. Moreover, at 348 K, uniform and highly ordered EG2 SAMs on Au(111) were formed with a (2 × 3√3) packing structure.

Stimulus-Responsive Tubular Conjugated Polymer 2D Nanosheets.

Creation of new two-dimensional (2D) architectures has attracted significant attention in the field of self-assembly for structural diversity and new functionalization. Although numerous 2D polymer nanosheets have been reported, 2D nanosheets with tubular channels have been unexplored. Herein, we describe a new strategy for the fabrication of stimulus-responsive conjugated polymer 2D nanosheets with hollow cavities.

Strainer-Separable TiO on Halloysite Nanocomposite-Embedded Alginate Capsules with Enhanced Photocatalytic Activity for Degradation of Organic Dyes.

Photocatalysis driven by natural sunlight is an attractive approach to removing pollutants from wastewater. Although TiO-based photocatalysts using various support nano-materials with high catalytic activity and reusability have been developed for purifying wastewater, the centrifugal separation methods used for the nanocatalysts limit their use for treating large amounts of water. Here, we prepared a TiO nano-catalyst supported on a halloysite nanotube (HNT)-encapsulated alginate capsule (TiO@HNT/Alcap) to recapture the catalysts rapidly without centrifugation.

Solvent- and Light-Sensitive AIEE-Active Azo Dye: From Spherical to 1D and 2D Assemblies.

Fluorescent molecular assembly systems provide an exciting platform for creating stimuli-responsive nano- and microstructured materials with optical, electronic, and sensing functions. To understand the relationship between (i) the plausible molecular structures preferentially adopted depending on the solvent polarity (such as N,N-dimethylformamide [DMF], tetrahydrofuran [THF], and toluene), (ii) the resulting spectroscopic features, and (iii) self-assembled nano-, micro-, and macrostructures, we chose a sterically crowded triangular azo dye (3Bu) composed of a polar molecular core and three peripheral biphenyl wings. The chromophore changed the solution color from yellow to pink-red depending on the solvent polarity.

Self-assembly using a retro Diels-Alder reaction.

Despite their great utility in synthetic and materials chemistry, Diels-Alder (DA) and retro Diels-Alder (rDA) reactions have been vastly unexplored in promoting self-assembly processes. Herein we describe the first example of a retro Diels-Alder (rDA) reaction-triggered self-assembly method. Release of the steric bulkiness associated with the bridged bicyclic DA adduct by the rDA reaction allowed generation of two building blocks that spontaneously self-assembled to form a supramolecular polymer.

Light-directed trapping of metastable intermediates in a self-assembly process.

Self-assembly is a dynamic process that often takes place through a stepwise pathway involving formation of kinetically favored metastable intermediates prior to generation of a thermodynamically preferred supramolecular framework. Although trapping intermediates in these pathways can provide significant information about both their nature and the overall self-assembly process, it is a challenging venture without altering temperature, concentrations, chemical compositions and morphologies. Herein, we report a highly efficient and potentially general method for "trapping" metastable intermediates in self-assembly processes that is based on a photopolymerization strategy.

Highly Efficient Adsorption of Anionic Dye on Acid-Treated Halloysite Nanotubes.

The adsorption capability of eosin Y as a model anionic dye on natural halloysite nanotubes (HNTs) and sulfuric acid-treated HNTs as a function of acid treatment time (1 h, 3 h, and 5 h) was examined. Scanning electron microscopy revealed that natural HNTs had a very uniform surface, whereas acid-treated HNTs had a rough surface with structural defects, which increased with acid treatment time. The total specific pore volume and total surface area of the acid-treated HNTs increased due to formation of nanopores in the HNTs via dissolution of the inner AlO octahedral layer.

Growth Processes and Reductive Desorption Behaviors of 4-Fluorobenzenethiol Self-Assembled Monolayers on Au(111).

Growth processes and electrochemical behaviors of 4-fluorobenzenethiol (4-FBT) self-assembled monolayers (SAMs) on Au(111) prepared by vapor deposition at 323 K were examined using scanning tunneling microscopy (STM) and cyclic voltammetry (CV). STM imaging revealed that 4-FBT SAMs at the initial growth stage (deposition for 1 min) were mainly composed of bright molecular aggregates and liquid-like disordered phase. After longer deposition for 3 min, 4-FBT SAMs had three distinct surface features: a few molecular aggregates, small ordered domains, and disordered phase.

Solvent Effect on the Formation of Octaneselenocyanate Self-Assembled Monolayers on Au(111).

Solvent effect on the formation and electrochemical behavior of octaneselenolate (C8Se) self-assembled monolayers (SAMs) on Au(111) derived from the adsorption of octaneselenocyanate (C8Se-CN) molecules in various solvents at 363 K for 1 h was examined by scanning tunneling microscopy (STM) and cyclic voltammetry (CV). STM imaging clearly revealed that the formation and structure of C8Se SAMs were markedly influenced by the polarity of solvent. C8Se SAMs formed in octane were composed of liquid-like disordered phase.

Displacement Processes of 1-Adamanetanethiol Self-Assembled Monolayers on Au(111) by 1-Hexanethiol.

Displacement processes of pre-adsorbed 1-admanetanethiol (ADT) self-assembled monolayers (SAMs) on Au(111) by 1-hexanethiol (HT) at room temperature were investigated by scanning tunneling microscopy (STM) and cyclic voltammetry (CV). Molecular-scale STM imaging clearly revealed that phase transitions from the (7 × 7) phase for ADT SAMs to the c(4 × 2) phase for HT SAMs via intermediate phase including bright aggregated islands and disordered phase. Moreover, it was found that ADT SAMs were completely displaced by HT molecules with a short hexyl chain within an hour.

Well-Ordered Domains of 4-Fluorobenzenethiol Self-Assembled Monolayers on Au(111) Guided by a Displacement Reaction.

Displacement processes of pre-covered cyclohexanethiol (CHT) self-assembled monolayers (SAMs) by 4-fluorobenzenethiol (4-FBT) on Au(111) were examined as a function of displacement time by scanning tunneling microscopy (STM) and water static contact angle (CA) measurements. STM imaging revealed that the adsorption of 4-FBT on Au(111) in a 1 mM ethanol solution at room temperature for 24 h generated disordered SAMs, whereas well-ordered 4-FBT SAMs with a (4√6 × √3)R5° packing structure were formed over the entire Au(111) surfaces via the displacement of pre-covered CHT SAMs by 4-FBT molecules. The CA measurements also showed that CA values increase with increasing displacement time, reflecting that the displacement reaction took place and the resulting SAMs had greater hydrophobicity compared with CHT SAMs.

Formation of Ordered 4-Fluorobenzenethiol Self-Assembled Monolayers on Au(111) from Vapor Phase Deposition.

Self-assembled monolayers (SAMs) were formed by the spontaneous adsorption of 4-fluorobenzenethiol (4-FBT) on Au(111) using both solution and ambient-pressure vapor deposition methods at room temperature. The surface structure and thermal desorption properties of 4-FBT SAMs were examined by scanning tunneling microscopy (STM) and thermal desorption spectroscopy (TDS). STM imaging showed that 4-FBT SAMs formed in solution at room temperature mainly contained disordered phase with gold adatom islands, while those formed by ambient-pressure vapor deposition had well-ordered phase, which can be described as a (2 x 2√13)R45 degrees structure.

Striped Phase of 3-Hexylthiophene Self-Assembled Monolayers on Au(1 11) Formed by Vapor Phase Deposition.

The formation and surface structure of 3-hexylthiophene (HTP) self-assembled monolayers (SAMs) on Au(111) prepared by solution and ambient-pressure vapor deposition at room temperature (RT) for 24 h were examined by means of scanning tunneling microscopy (STM) and cyclic voltammetry (CV). STM imaging revealed that HTP SAMs formed by solution deposition have a disordered phase, whereas those formed by vapor deposition exhibit a striped phase with a unidirectional orientation. The distance between the rows in the striped phase was measured to be 1.

Structural Stability and Phase Transitions of Octanethiol Self-Assembled Monolayers on Au(111) in Ultrahigh Vacuum.

To understand the structural stability of as-prepared octanethiol (OT) self-assembled monolayers (SAMs) with a fully covered c(4 x 2) phase on Au(111) in ultrahigh vacuum (UHV) conditions of 3 x 10(-7) Pa at room temperature, we examined OT SAM samples obtained as a function of storage period using scanning tunneling microscopy (STM). STM imaging revealed that phase transition of OT SAMs after storage in UHV for 3 days occurs from the c(4 x 2) phase to the mixed phase containing ordered c(4 x 2) and disordered phases. It was also observed that the disordered phase was mainly located at around vacancy islands and near step edges of Au(111) terraces, implying that desorption of OT molecules chemisorbed on Au(111) in UHV occurs more quickly in these regions compared with in the closely packed and ordered domains.

Effect of Solution Concentration on the Formation of Ordered Domains in Pentachlorobenzenethiol Self-Assembled Monolayers on Au(111).

The surface structures of self-assembled monolayers (SAMs) formed by the adsorption of pentachlorobenzenethiol (PCBT) molecules on Au(111) as a function of solution concentration were examined by means of scanning tunneling microscopy (STM) to understand the effect of concentration on the formation of ordered domains. STM imaging revealed that PCBT SAMs formed in a 0.01 or 1 mM ethanol solution at room temperature for 20 min contained small ordered domains in the range of several to 20 nm2 and disordered phases, while PCBT SAMs formed in a 0.

Thermal curing of a self-assembled monolayer at the nanoscale.

On fabrication by contact printing, a nanostructured self-assembled monolayer (SAM) of alkanethiol contains a substantial fraction of unbound molecules that are either inverted among other upright molecules or piled on top of the SAM. The molecular dynamics simulation in the present study demonstrates that thermal annealing cures these defects for a SAM island of octadecanethiol. The SAM island melted partially as a result of heating, so the unbound molecules that had piled on top of the SAM island penetrated down to make contact with the surface, and the inverted molecules flipped to achieve adsorption.

Enhancement of the Luminance Efficiency in Organic Light-Emitting Devices with p-Substituted Phenylphosphonic-Acid Self-Assembled Monolayers.

Organic light-emitting devices (OLEDs) containing self-assembled monolayers (SAMs) prepared by using p-substituted phenylphosponic acids on indium-tin-oxide electrodes were fabricated and examined to understand the substituent effect of the SAMs on the device performance. OLEDs modified by using (4-methoxyphenyl)phosphonic acid (MOPPA) SAMs or (4-chlorophenyl)phosphonic acid (CPPA) SAMs, both with electron withdrawing groups, had enhanced hole injection, reduced operating voltage, and remarkably increased current density and luminance efficiency compared with those without SAMs. The luminance efficiency which was the ratio of luminous flux to power for OLEDs containing CPPA SAMs and that for the OLEDs containing MOPPA SAMs were enhanced 2.

Ripple-Free Graphene Sheets on Alkanethiol Self-Assembled Monolayers Provided from Unzipped Multi-Walled Carbon Nanotubes.

Octanethiol (C8S, CH3(CH2)7SH) self-assembled monolayers/Au(111) were utilized as an inert surface to provide ripple-free graphene oxide layers provided from chemically unzipped multi-walled carbon nanotubes (MWCNTs). The resulting graphene oxide monolayers were characterized with atomic resolution by UHV-STM. The honeycomb structure for the graphene monolayer and "three-for-six" triangular pattern for the multi-layer graphene sheets on C8S SAMs were clearly observed without ripples by the high-resolution UHV-STM.

Formation and structure of ordered pentachlorobenzenethiol self-assembled monolayers on Au(111) studied by scanning tunneling microscopy.

Molecular-scale surface structures of self-assembled monolayers (SAMs) prepared by the adsorption of pentafluorobenzenethiols (PFBT) and pentachlorobenzenethiols (PCBT) on Au(111) were investigated by scanning tunneling microscopy (STM). High-resolution STM imaging revealed that PFBT SAMs on Au(111) have long-range ordered domains with a row structure at room temperature, whereas PCBT SAMs have small ordered domains, with disordered domains as the main phase. This may reflect the larger diffusion barriers of PCBT molecules on Au(111) surfaces compared to PFBT molecules during SAM formation.

Effect of molecular desorption on the electronic properties of self-assembled polarizable molecular monolayers.

We investigated the interfacial electronic properties of self-assembled monolayers (SAM)-modified Au metal surface at elevated temperatures. We observed that the work functions of the Au metal surfaces modified with SAMs changed differently under elevated-temperature conditions based on the type of SAMs categorized by three different features based on chemical anchoring group, molecular backbone structure, and the direction of the dipole moment. The temperature-dependent work function of the SAM-modified Au metal could be explained in terms of the molecular binding energy and the thermal stability of the SAMs, which were investigated with thermal desorption spectroscopic measurements and were explained with molecular modeling.

A new arene-Ru based supramolecular coordination complex for efficient binding and selective sensing of green fluorescent protein.

A new dipyridyl ligand is encoded with 120° angularity between its coordination vectors by using a central pyridine carboxamide scaffold to orient two 4-(pyridin-4-ylethynyl)phenyl moieties. The N,N'-bis(4-(pyridin-4-ylethynyl)phenyl)pyridine-2,6-dicarboxamide ligand undergoes self-assembly with a diruthenium arene complex to furnish a [2 + 2] metallacycle with a wedge-like structure. The metallacycle binds to the enhanced green fluorescent protein (EGFP) variant of GFP, resulting in steady-state spectral changes in UV-Vis absorption and emission experiments.

Growth, solvent effects, and thermal desorption behavior of octylthiocyanate self-assembled monolayers on Au(111).

The growth process, solvent effects, and thermal desorption behavior of octylthiocyanate [OTC, CH(3)(CH(2))(7)S-CN] self-assembled monolayers (SAMs) on Au(111) were characterized by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). To investigate their growth processes, octanethiol [OT, CH(3)(CH(2))(7)S-H] and OTC SAMs were prepared in 0.5 μM ethanol solution at room temperature as a function of immersion time: 10 min, 1 h, 2 h, and 24 h.