Gels with sense: supramolecular materials that respond to heat, light and sound

Advances in the field of supramolecular chemistry have made it possible, in many situations, to reliably engineer soft materials to address a specific technological problem. Particularly exciting are "smart" gels that undergo reversible physical changes on exposure to remote, non-invasive environmental stimuli. This review explores the development of gels which are transformed by heat, light and ultrasound, as well as other mechanical inputs, applied voltages and magnetic fields. Focusing on small-molecule gelators, but with reference to organic polymers and metal-organic systems, we examine how the structures of gelator assemblies influence the physical and chemical mechanisms leading to thermo-, photo- and mechano-switchable behaviour. In addition, we evaluate how the unique and versatile properties of smart materials may be exploited in a wide range of applications, including catalysis, crystal growth, ion sensing, drug delivery, data storage and biomaterial replacement.

[Synthesis, Aggregation, Self-assembly, and Dynamic Properties of Helicene Oligomers]

 Biological systems exhibit dynamic phenomena at the macroscopic level as a result of the hierarchical integration of phenomena at the molecular level. For example, a number of amino acids compose actin proteins, which form three-dimensional structures determined by the sequence of amino acids. They form fibers by self-assembly, which then form ordered structures such as meshes, lyotropic liquid crystals (LCs), and bundles. The dynamic and reversible polymorphism between these nano- to centimeter-sized ordered structures is essential for biological functions such as cell division, contraction, and locomotion. To understand biological systems and create new functional materials, it is essential to develop a methodology to integrate phenomena at the molecular level into those at the macroscopic level using synthetic molecules. In this research, synthetic oligomers containing helicenes, which exhibit reversible structural transitions between cylindrical double helices and random coils in response to thermal stimuli, were employed as building blocks for the development of such a methodology. The properties of homo- and hetero-double helices at the molecular level were first controlled by taking advantage of the diversity of their molecular structures. Then, nano- to micrometer-sized structures were constructed by the self-assembly of hetero-double helices, which include fibers/gels, vesicles, and lyotropic LCs, and their dynamic properties were controlled by molecular design.

Self-assembled chiral helical nanofibers by amphiphilic dipeptide derived from d- or l-threonine and application as a template for the synthesis of Au and Ag nanoparticles

The discovery of a class of self-assembling peptides that spontaneously undergo self-organization into well-ordered structures opened a new avenue for molecular fabrication of biological materials. In this paper, the structure controlled helical nanofibers were prepared by two artificial β-sheet dipeptides with long alkyl chains derived from l- and d-threonine (Thr) and sodium hydroxide (NaOH). These helical nanofibers have been characterized using transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), circular dichroism (CD), Fourier transform infrared (FT-IR) spectroscopy, and X-ray powder diffraction (XRD). It was demonstrated that the helicity of the nanofibers could be easily controlled by changing the chirality of the constituent amino acids in the peptide species (d- or l-threonine). Moreover, the hydrogen bonding interactions between the amide groups as well as the hydrophobic interactions among the alkyl chains play important roles in the self-assembly process. It also can be observed that with the passage of time, the hydrogen bonding interactions between the individual nanofiber induced the conversion from nanofibers to nanobelts. Particularly, gold and silver nanoparticles performed good catalytic ability were synthesized using the assembled nanofibers as template.

Effects of carbon nanomaterials on the aggregation of a bi-oxadiazole derivative (BOXD-T8) in DMF and its gel properties

SWNTs hybrid xerogel consisted of spherical aggregates with both graphene sheets and entangled fibers for the GO hybrid system.

Unimolecular photoconversion of multicolor luminescence on hierarchical self-assemblies

Facile tuning of photophysical properties is highly desirable for boosting the performance and versatility of photoluminescent materials. In an attempt to overcome the challenge of achieving the photoswitching of multicolor luminescence on unimolecular platforms, we here report a novel hierarchical self-assembly of a cyanostilbene-naphthalimide dyad as the realization of phototunable luminescence at the unimolecular level. The work takes advantage of the photoisomerization of the cyanostilbene moiety from the Z form to its E form, which causes a morphological disorder in the molecular self-assembly and gives rise to a dual fluorescent characteristic accompanied by a progressive luminescent color conversion from yellow to green and finally to blue. Such systems with convertible multicolor luminescence might exhibit application potentials for unimolecular selective imaging and labeling, as exemplified by the cell imaging studies presented in this work.