Guanglu Wu

Bolaform Supramolecular Amphiphiles as a Novel Concept for the Buildup of Surface-Imprinted Films

Stable multilayer films were fabricated on the basis of the alternating layer-by-layer assembly of a two-component bolaform supramolecular amphiphile and diazoresins, followed by photochemical cross-linking of the structure. UV-visible spectroscopy and atomic force microscopy revealed a uniform deposition process. Moreover, one component of the supramolecular amphiphile can be removed from the multilayer films after cross-linking between the second component and the diazoresin. The release and uptake of the imprinted supramolecular amphiphile component are shown to be reversible. Furthermore, uptake experiments of different molecules show the selectivity of the imprinted sites for the template molecule. Thus, surface-imprinted films can be formed by employing dissociable two-component supramolecular amphiphiles. This research reveals that supramolecular amphiphiles can be used as a novel concept for the construction of multilayer films, and it also provides a new method of generating surface-imprinted multilayers.

Controlling the self-assembly of cationic bolaamphiphiles

Self-assembly of cationic bolaamphiphiles is usually reported to form one-dimensional (1D) or zero-dimensional (0D), rather than two-dimensional (2D) structures. Here we have found a facile counterion-directed structure switch for such amphiphilic moieties. 0D/1D structures formed by self-assembly of cationic bolaamphiphiles can be converted into 2D planar structures by a simple counterion change to tosylate. As indicated by the single crystal structure and variable-temperature NMR studies, the strong binding between tosylate counterions and cationic headgroups drives the formation of 2D planar structures. It is highly anticipated that this approach may present as a simple methodology to control the stacking of the embedded conjugated cores in bolaamphiphiles, therefore modulating optoelectronic properties and function in such assemblies.

Bolaamphiphiles Bearing Bipyridine as Mesogenic Core: Rational Exploitation of Molecular Architectures for Controlled Self-Assembly

A bolaamphiphile (5,5-B2NBr8) bearing a functional bipyridine moiety as the mesogenic core is reported for the first time. 5,5-B2NBr8 was found to self-assemble into uniform fibrous structure in aqueous solution, when the concentration was higher than cmc. Analogues of 5,5-B2NBr8 with structural differences in chain length, headgroup, mesogenic core, and substituted position were synthesized, elucidating that small variances of the molecular structure could lead to dramatic changes of the resulting assemblies. For example, compound 4,4-B2NBr8 showed only spherical colloidal aggregates rather than fibers as 5,5-B2NBr8 did, while the only difference between them was the position at which the alkyl chains were attached onto bipyridine. A probable model for the fibrous structure of 5,5-B2NBr8 was proposed. Moreover, exploiting the coordination capacity of bipyridine, assembly and disassembly of 5,5-B2NBr8 could be reversibly controlled through the addition of EDTA and Cu(II), respectively.

Poly(acrylic acid)-bearing photoreactive azido groups for stabilizing multilayer films.

In this article, we have demonstrated a universal method for improving the stability of polyelectrolyte multilayer films by designing a photoreactive polyanion as the building block for layer-by-layer (LbL) self-assembly. By grafting an azido group into poly(acrylic acid), we synthesized a photoreactive polyanion, which can induce the photo-crosslinking between the azido group and polymeric backbone under UV irradiation. Our results show that after photocross-linking, the stability of the polyelectrolyte multilayer is greatly improved. Considering that the polyanion-bearing azido group is highly reactive, we have shown that it can be used to stabilize different LbL films. Moreover, by taking advantage of the different stability before and after UV irradiation, a patterned surface can be fabricated, which could be used as a template for selective adsorption.

Self-Assembly of a Functional Oligo(Aniline)-Based Amphiphile into Helical Conductive Nanowires

A tetra(aniline)-based cationic amphiphile, TANI-NHC(O)C5H10N(CH3)3+Br– (TANI-PTAB) was synthesized, and its emeraldine base (EB) state was found to self-assemble into nanowires in aqueous solution. The observed self-assembly is described by an isodesmic model, as shown by temperature-dependent UV–vis investigations. Linear dichroism (LD) studies, combined with computational modeling using time-dependent density functional theory (TD-DFT), suggests that TANI-PTAB molecules are ordered in an antiparallel arrangement within nanowires, with the long axis of TANI-PTAB arranged perpendicular to the nanowire long axis. Addition of either S- or R- camphorsulfonic acid (CSA) to TANI-PTAB converted TANI to the emeraldine salt (ES), which retained the ability to form nanowires. Acid doping of TANI-PTAB had a profound effect on the nanowire morphology, as the CSA counterions’ chirality translated into helical twisting of the nanowires, as observed by circular dichroism (CD). Finally, the electrical conductivity of CSA-doped helical nanowire thin films processed from aqueous solution was 2.7 mS cm–1. The conductivity, control over self-assembled 1D structure and water-solubility demonstrate these materials’ promise as processable and addressable functional materials for molecular electronics, redox-controlled materials and sensing.

Supra-amphiphiles formed by complexation of azulene-based amphiphiles and pyrene in aqueous solution: from cylindrical micelles to disklike nanosheets

We have fabricated supra-amphiphiles by charge-transfer complexation of azulene-based amphiphiles and pyrene in water, and the self-assembled nanostructures can reversibly change between cylindrical micelles and disklike nanosheets in response to interaction with guest molecules.

Controlling the self-assembly of cationic bolaamphiphiles: hydrotropic counteranions determine aggregated structures

The role of hydrotropic counteranions in governing the self-assembled structures of cationic bolaamphiphiles is studied in this work. We reveal that the ability of a hydrotropic counteranion to induce the formation of two-dimensional (2D) planar aggregates depends weakly on its polar head, but is strongly correlated to the size and substitution pattern of its organic portion. Additionally, the shape of the obtained 2D planar aggregates can be modulated, interestingly, by both hydrotropic counteranions and embedded conjugated moieties. 2D planar aggregates with triangular, quadrangular, and hexagonal shapes are obtained, and therefore this study may provide a simple and feasible methodology for fabricating organic self-assembled structures with controlled features.

Generation of 2D organic microsheets from protonated melamine derivatives: suppression of the self assembly of a particular dimension by introduction of alkyl chains

Dialkylated melamine derivatives self-assemble with halogen acids into 2D organic microsheets in organic solvent through counterion bridged multiple hydrogen bonds as well as electrostatic interactions and π–π stacking. Alkyl chains are introduced to suppress the growth in a particular dimension, supplying a general approach for the fabrication of 2D structures. Protonation is demonstrated to be a crucial factor in the formation of 2D assemblies. The assembly and disassembly of microsheets can be reversibly controlled by alternating addition of acid and base. Even the aspect ratio of the rectangular microsheets can be further modulated through the addition of different amounts of acid.

Selectively Erasable Multilayer Thin Film by Photoinduced Disassembly

A multilayer film consisting of poly(acrylic acid) (PAA) and an azobenzene-containing surfactant (AzoTEA) was fabricated via a layer-by-layer assembly technique. The micellar structure favored by AzoTEA while in solution results in a bilayer structure when deposited on a substrate surface. This aggregation conversion behavior favors the deposition of AzoTEA and PAA in an alternating pattern to form a photoresponsive multilayer film. The molecular amphiphilicity of AzoTEA can be tuned by photoisomerization of the azobenzene moiety, which affects the aggregation behavior of AzoTEA in both films and solutions. The disassembly of AzoTEA aggregates caused by photoirradiation can induce the disassembly of the whole multilayer film. The AzoTEA-PAA multilayer films were found to be stable in pH 4 acetic acid (AcOH) solution, unless treated with UV radiation. On the basis of the different stability of multilayers with or without photoirradiation, when the multilayer films are selectively irradiated with UV light, the regions exposed to UV radiation disassembled after being immersed in pH 4 AcOH solution for 10 min but the regions not exposed to photoradiation are maintained on the substrate. Moreover, the plausible mechanism for the assembly and disassembly of these multilayer films and the confirmation of erasable films by atomic force microscopy are discussed.

Mono-molecule-layer nano-ribbons formed by self-assembly of bolaamphiphiles

Amphiphilic molecules generally tend to organize spontaneously into spherical or cylindrical micelles/vesicles in appropriate liquid media and conditions, and seldom form two dimensional (2D) planar structures with a regular shape, due to their energetically unfavorable state. Herein, the self-assembly of a new bolaamphiphile bearing a bistriazole-pyrene unit leads to the formation of mono-molecule-layer nano-ribbons. The π-π stacking interaction between the rigid bistriazole-pyrene units and electrostatic screening contributed by the aromatic counterion tosyl groups are responsible for the 2D alignment of the molecules in the aggregate. Partial replacement of the tosyl groups causes a reduction in the width of the nano-ribbons and the coordination of triazole with Pd2+ ions results in the collapse of the self-assembled structure. This study supplies new clues for fabricating molecular level 2D nanostructures by bottom-up supramolecular assembly.