Dye-based organogels: Stimuli-responsive soft materials based on one-dimensional self-assembling aromatic dyes

In this review, low molecular-weight organogel based on aromatic dye molecules and its stimuli-responsiveness were summarized. Aromatic dyes from small and medium aromatics such as azobenzene, pyrene, bithiophene, tropone, and merocyanine to large aromatics such as porphyrin, phthalocyanine, fullerene, triphenylene, hexaazatriphenylene, and phenylenevinylene, are self-assembled and self-organized in organogel systems to afford a new class of dye-based supramolecular assemblies. In certain solvents, aromatic dye molecules are stacked one-dimensionally to form the elongated columnar-type fibrous aggregates, which are entangled into three-dimensional network structures to prevent the solvents from flowing, leading to viscoelastic fluid "organogel". π - π stacking forces among core aromatic moieties and secondary noncovalent interactions such as hydrogen-bonding and van der Waals interactions cooperatively stabilize the supramolecular structures constructed in the organogel. The noncovalent assembling in the organogel organization is reflected in their reversible sol-gel phase transition controlled by physical or chemical stimuli such as thermo-, photo-, chemo-, metal-, proton-, and mechano-stimuli. By utilizing the columnar-type fibrous structure and the stimuli-responsiveness, the organogels can be engineered to show novel functions such as guest-recognizing, light-harvesting, carrier-transporting, and memory storage properties in soft materials.