Vesicle Formation from an Amphiphilic Porphyrin Derivative at the Air–Water Interface

A tetraphenyl porphyrin derivative with two C₁₆ alkyl chains covalently bound to each of the four peripheral phenyl rings through ether linkages formed multilayer clusters or vesicles at the air–water surface. More interestingly, spherical vesicles were also formed when deposited on appropriate solid surfaces, and these vesicles were stable even in dry conditions. Various microscopic images of the cast film deposited on a mica surface confirmed closed‐ended nanotube/nanorod‐type formation with necking and bulging. These narrow tubes are proposed to be intermediates for the formation of vesicles by fission at either side of the bulge. Such vesicular formation is not common when either cast or Langmuir–Blodgett films were deposited on a solid surface.     

pH‐Modulated Molecular Assemblies and Surface Properties of Metal–Organic Supercontainers at the Air–Water Interface

The orientation of metal–organic supercontainer (MOSC) molecules in Langmuir films was systematically studied at the air–water interface. The acidity of the aqueous subphases plays a significant role in tuning the orientation of MOSC molecules in the Langmuir films. Furthermore, Langmuir–Blodgett films of MOSCs were prepared and the uniform multilayer structures demonstrated various surface properties, depending on their conditions of fabrication. Our use of Langmuir films provides a novel approach to access tunable assemblies of MOSC molecules in two‐dimensional thin films.     

Towards the Fabrication of the Top‐Contact Electrode in Molecular Junctions by Photoreduction of a Metal Precursor

Langmuir films of 4‐{[4‐({4‐[(trimethylsilyl)ethynyl]phenyl}ethynyl)phenyl]ethynyl} benzenaminium chloride ([ 1 H ]Cl) undergo anion metathesis when assembled on an aqueous auric acid (HAuCl₄) subphase. Subsequent transfer to solid supports gives well‐formed Langmuir–Blodgett (LB) monolayers of [ 1 H ]AuCl₄ in which the trimethylsilyl group serves as the surface contacting group. Photoreduction of the aurate on these monolayers leads to the formation of metallic gold nanoislands, which were distributed over the surface of the film. Electrical properties of these nascent devices were determined by recording current–voltage (I–V) curves with conductive atomic force microscopy (c‐AFM) using the PeakForce tunneling AFM (PF‐TUNA) mode. This gives consistent sigmoidal I–V curves that are indicative of well‐behaved junctions free of metallic filaments and short circuits. The photoreduction of a metal precursor incorporated onto monomolecular films is therefore proposed as an effective method for the fabrication of molecular junctions.     

Colloidal Microcapsules: Self‐Assembly of Nanoparticles at the Liquid–Liquid Interface

Colloidal microcapsules (MCs) are highly modular, inherently multiscale constructs of capsules stabilized by nano‐/microparticle shells, with applications in many areas of materials and biological sciences, such as drug delivery, encapsulation, and microreactors. Until recently, fabrication of colloidal MCs focused on the use of submicron‐sized particles because the smaller nanoparticles (NPs) are inherently unstable at the interface owing to thermal disorder. However, stable microcapsules can now be obtained by tuning the interactions between the nanometer‐sized building blocks at the liquid–liquid interface. This Review highlights recent developments in the fabrication of colloidal MCs using NPs.     

Artificial Iono‐ and Photosensitive Membranes Based on an Amphiphilic Aza‐Crown‐Substituted Hemicyanine

Artificial iono‐ and photosensitive membranes based on an amphiphilic aza‐crown‐substituted hemicyanine are assembled on liquid and solid supports and their aggregation behaviour, which is influenced by the binding of metal cations and surface density, is studied. The photoinduced charge‐transfer properties of an analogous non‐amphiphilic hemicyanine in solution are also demonstrated. An asymmetric sandwich dimer model is proposed and existence of such dimers in solution is evidenced by transient absorption and fluorescence anisotropy experiments. Changes in absorption and emission spectra, as well as compression isotherms of the amphiphile observed in the presence of cations, are discussed in terms of 2D molecular reorganisation. Surface‐pressure‐controlled reversible excimer formation at the air–water interphase and excimer‐type emission of Langmuir–Blodgett films in the presence of cations are demonstrated and are discussed on the basis of fibre‐optic fluorimetry and fluorescence microscopy results.     

Compression of Self‐Assembled Nano‐Objects: 2D/3D Transitions in Films of (Perfluoroalkyl)Alkanes—Persistence of an Organized Array of Surface Micelles

Understanding and controlling the molecular organization of amphiphilic molecules at interfaces is essential for materials and biological sciences. When spread on water, the model amphiphiles constituted by C_nF_2n+1C_mH_2m+1 (FnHm) diblocks spontaneously self‐assemble into surface hemimicelles. Therefore, compression of monolayers of FnHm diblocks is actually a compression of nanometric objects. Langmuir films of F8H16, F8H18, F8H20, and F10H16 can actually be compressed far beyond the “collapse” of their monolayers at ～30 Ų. For molecular areas A between 30 and 10 Ų, a partially reversible, 2D/3D transition occurs between a monolayer of surface micelles and a multilayer that coexist on a large plateau. For A<10 Ų, surface pressure increases again, reaching up to ～48 mN m^?1 before the film eventually collapses. Brewster angle microscopy and AFM indicate a several‐fold increase in film thickness when scanning through the 2D/3D coexistence plateau. Compression beyond the plateau leads to a further increase in film thickness and, eventually, to film disruption. Reversibility was assessed by using compression–expansion cycles. AFM of F8H20 films shows that the initial monolayer of micelles is progressively covered by one (and eventually two) bilayers, which leads to a hitherto unknown organized composite arrangement. Compression of films of the more rigid F10H16 results in crystalline‐like inflorescences. For both diblocks, a hexagonal array of surface micelles is consistently seen, even when the 3D structures eventually disrupt, which means that this monolayer persists throughout the compression experiments. Two examples of pressure‐driven transformations of films of self‐assembled objects are thus provided. These observations further illustrate the powerful self‐assembling capacity of perfluoroalkyl chains.     

Acetone‐Induced Graphene Oxide Film Formation at the Water–Air Interface

Graphene oxide (GO) is an amphiphilic soft material, which can accumulate at the water–air interface. However, GO sheets diffuse slowly in the aqueous phase because of their large size. It is still challenging to form high quality GO films in a controllable and simple way. In this study, we showed that GO sheets can quickly migrate to the water–air interface and form thin films when a suitable amount of acetone is directly mixed with a GO aqueous dispersion. The film formation rate and surface coverage of GO sheets depend on the volume of acetone added, GO dispersion concentration, and formation time. Among several organic solvents, acetone has its advantage for GO film formation owing to its three properties: a nonsolvent to GO aqueous dispersions, miscible with a GO aqueous dispersion, and fast evaporation. Furthermore, we have found that the film formation also is governed by the size of GO sheets and their oxygen content. Although smaller GO sheets could migrate to the water–air interface faster, the overlapping of small GO sheets and the increase in contact resistance is not desirable. A higher oxygen content in GO sheets could also result in smaller GO sheets. Multilayer GO films can be obtained through layer‐by‐layer dip‐coating. These findings open opportunities in developing simple scalable GO film fabrication processes.     

Synthesis of an Open‐Cage Structure POSS Containing Various Functional Groups and Their Effect on the Formation and Properties of Langmuir Monolayers

Recently, silsesquioxanes have been recognized as a new group of film‐forming materials. This study has been aimed at determining the effect of the kind of functional groups present in two different open‐cage structure POSS molecules on the possibility of the formation of Langmuir monolayers and their properties. To achieve this goal, two new POSS derivatives (of open‐cage structures) containing polyether and fluoroalkyl functional groups have been synthesized on the basis of a hydrosilylation process. An optimization of the process was performed, which makes it possible to obtain the above‐mentioned derivatives with high yields. In the next step, the Langmuir technique was applied to measurements of the surface pressure (π) ? the mean molecular area (A) isotherms during the compression of monolayers formed by molecules of the two POSS derivatives considered. Subsequently, the monolayers were transferred onto quartz plates according to the Langmuir–Blodgett technique. Both derivatives are able to form insoluble Langmuir films at the air–water interface, which can be transferred onto a solid substrate and effectively change its wetting properties.     

Zinc Porphyrin Metal‐Center Exchange at the Solid–Liquid Interface

Demetalation of zinc 5,10,15,20‐tetraphenylporphyrin (ZnTPP) under acidic conditions and ion exchange with Cu²⁺ ions at neutral pH are both rapid reactions in the liquid medium. However, for ZnTPP monolayers adsorbed on a Au(111) surface exposed to aqueous solution, we find that, although ion exchange takes place rapidly as expected, demetalation does not occur, even at pH values as low as 0. Based on this, we conclude that metal center exchange on the surface does not proceed through a free‐base porphyrin as an intermediate. Furthermore, once formed, CuTPP is stable on the surface and the reverse exchange from CuTPP to ZnTPP in the presence of Zn²⁺ ions could not be achieved. The preference for copper is so strong that even an attempt to exchange adsorbed ZnTPP with Ni²⁺ ions in the presence of traces of Cu²⁺ yielded CuTPP rather than NiTPP.     

One‐Step Synthesis of Hybrid Liquid–Crystal ZnO Nanoparticles: Existence of a Critical Temperature Associated with the Anisotropy of the Nanoparticles

Zinc oxide nanoparticles were obtained from the hydrolysis of an organometallic precursor in pure hexadecylamine. Interestingly, we demonstrate that the final (anisotropic or isotropic) shape of the nanoparticles is strongly correlated to the existence of a critical temperature. This suggests that the organization of the fatty amines is a paramount parameter in this synthesis. Moreover, the final hybrid ZnO materials systematically exhibit a liquid–crystal smectic phase, whereas no liquid–crystal phase was observed in the pristine reaction media. This simple process is, therefore, a direct and straightforward method to synthesize liquid–crystal hybrid materials.     

Fullerene‐Filled Liquid‐Crystal Stars: A Supramolecular Click Mechanism for the Generation of Tailored Donor–Acceptor Assemblies

Two shape‐persistent star mesogens with oligo(phenylene ethenylene) arms and a phthalocyanine core—one providing free space ( 2 ) and one sterically encumbered by four fullerenes attached through spacers ( 3 )—have been successfully synthesized. In contrast to the smaller discotic derivative 1 , mesogen 2 forms a columnar liquid crystal (LC), which can only be partially aligned without π‐stacking, while 3 is not an LC. Exceptionally, the 1:1 mixture of 2 and 3 forms an alignable columnar LC with strong π‐stacking and quadruply helically organized fullerenes by an unprecedented click process that is similar to a ball detent mechanism. The C₆₀ units also interconnect different columns. This is driven by nanosegregation and space‐filling of the voids with fullerenes. Photophysical studies confirm the presence of a light‐collecting system that generates charge‐separated states in solution and in the solid state, which makes such highly organized materials attractive for the study of future photovoltaic devices.     

A Two‐Dimensional Polymer Synthesized at the Air/Water Interface

A trifunctional, partially fluorinated anthracene‐substituted triptycene monomer was spread at an air/water interface into a monolayer, which was transformed into a long‐range‐ordered 2D polymer by irradiation with a standard UV lamp. The polymer was analyzed by Brewster angle microscopy, scanning tunneling microscopy measurements, and non‐contact atomic force microscopy, which confirmed the generation of a network structure with lattice parameters that are virtually identical to a structural model network based on X‐ray diffractometry of a closely related 2D polymer. The nc‐AFM images highlight the long‐range order over areas of at least 300×300 nm². As required for a 2D polymer, the pore sizes are monodisperse, except for the regions where the network is somewhat stretched because it spans over protrusions. Together with a previous report on the nature of the cross‐links in this network, the structural information provided herein leaves no doubt that a 2D polymer has been synthesized under ambient conditions at an air/water interface.