Light-controlled micron-scale molecular motion

The micron-scale movement of biomolecules along supramolecular pathways, mastered by nature, is a remarkable system requiring strong yet reversible interactions between components under the action of a suitable stimulus. Responsive microscopic systems using a variety of stimuli have demonstrated impressive relative molecular motion. However, locating the position of a movable object that travels along self-assembled fibres under an irresistible force has yet to be achieved. Here, we describe a purely supramolecular system where a molecular 'traveller' moves along a 'path' over several microns when irradiated with visible light. Real-time imaging of the motion in the solvated state using total internal reflection fluorescence microscopy shows that anionic porphyrin molecules move along the fibres of a bis-imidazolium gel upon irradiation. Slight solvent changes mean movement and restructuring of the fibres giving microtoroids, indicating control of motion by fibre mechanics with solvent composition. The insight provided here may lead to the development of artificial travellers that can perform catalytic and other functions.

(Super)gelators derived from push–pull chromophores: synthesis, gelling properties and second harmonic generation

New organogelators including push–pull chromophores are described and show that second harmonic generation active materials can be prepared without sophisticated processes.

Self-assembled nanostructures of amphiphilic zinc(II) salophen complexes: role of the solvent on their structure and morphology

This contribution explores the effect of several solvent properties, such as volatility, polarity, and Lewis basicity on the formation of molecular self-assembled nanostructures in the solid state, obtained either by casting of related solutions or by complete solvent evaporation, using seven solvents representative of common classes of coordinating organic solvents, of an amphiphilic Zn(II) Schiff-base complex. In all cases, the existence of well-defined X-ray diffraction patterns, for both the cast and powder samples, indicates a strong tendency towards the molecular self-assembly of such complexes. While nanostructures formed in acetone, THF, pyridine, and DMF have a lamellar organization, those formed in ACN, ethanol, and DMSO exhibit a 2D columnar square structure. Field emission scanning electron microscopy analysis indicates that nanostructures formed in volatile acetone, THF, ACN, and ethanol solvents show a fibrous morphology, while those formed in less volatile pyridine, DMF, and DMSO have a ribbon appearance. Overall, the results indicate that while the formation of such nanostructures is independent of the Lewis basicity of the solvent, the solvent polarity affects their structure - more polar solvents favour higher symmetry structures - and the solvent volatility influences their morphology and ordering in the cast films - lower volatility of the solvent parallels the formation of much more ordered structures. Therefore, the appropriate choice of solvent allows control of the structure, morphology, and ordering of these molecular assemblies.

Revisiting urea-based gelators: strong solvent- and casting-microstructure dependencies and organogel processing using an alumina template

Microstructures obtained from simple gelators prove to be strongly solvent- and casting-dependent. For the first time, a membrane template was used to process a xerogel-type material.

Self-assembled gelators for organic electronics

Nature excels at engineering materials by using the principles of chemical synthesis and molecular self-assembly with the help of noncovalent forces. Learning from these phenomena, scientists have been able to create a variety of self-assembled artificial materials of different size, shapes, and properties for wide ranging applications. An area of great interest in this regard is solvent-assisted gel formation with functional organic molecules, thus leading to one-dimensional fibers. Such fibers have improved electronic properties and are potential soft materials for organic electronic devices, particularly in bulk heterojunction solar cells. Described herein is how molecular self-assembly, which was originally proposed as a simple laboratory curiosity, has helped the evolution of a variety of soft functional materials useful for advanced electronic devices such as organic field-effect transistors and organic solar cells. Highlights on some of the recent developments are discussed.

Boosting electrical conductivity in a gel-derived material by nanostructuring with trace carbon nanotubes

An organogelator with two distinct π-functional units is able to incorporate carbon nanotubes into its mesh of fibres in the gel state. The morphology of the material derived from this nanocomposite after evaporation of the solvent is a complex mesh of fibres which is clearly different from the pure gelator. This feature indicates a role of the nanotubes in assisting the formation of a fibre structure in the gel thanks to their interaction with the pyrene units in the organogelator. The nanocomposite conducts electricity once the p-type gelator is doped with iodine vapour. The change in morphology caused by the carbon material increases the conductivity of the material compared with the purely organic conducting system. It is remarkable that this improvement in the physical property is caused by an extremely small proportion of the carbon material (only present at a ratio of 0.1% w/w). The practically unique properties of TTF unit allow measurements with both doped and undoped materials with conducting atomic force microscopy which have demonstrated that the carbon nanotubes are not directly responsible for the increased conductivity.