Fast and Reversibly Humidity-Responsive Fluorescence Based on AIEgen Proton Transfer.

The construction of humidity-responsive fluorescent materials with reversibility, specificity, and sensitivity is of great importance for the development of information encryption, fluorescence patterning, and sensors. Nevertheless, to date, the application of these materials has been limited by their slow response rate and nonspecificity. Herein, a humidity-responsive fluorescence system was designed and assembled to achieve a rapid, reversible, and specific moisture response. The system comprised tetra-(4-pyridylphenyl)ethylene (TPE-4Py) as a fluorescent proton acceptor with an aggregation-induced emission (AIE) effect and poly(acrylic acid) (PAA) as a proton donor with an efficient moisture-capturing ability. The fluorescence color and intensity rapidly changed with increasing relative humidity (RH) because of TPE-4Py protonation, and TPE-4Py deprotonation resulted in recovery of the original fluorescence color in low-humidity environments. The proton transfer between the pyridyl group in TPE-4Py and the carboxyl group in PAA was reversible and chemically stable, and the humidity-responsive fluorescence system showed a high response/recovery speed, an obvious color change, good reversibility, and an outstanding specific moisture response. Because of these advantages, diverse applications of this humidity-responsive fluorescence system in transient fluorescent patterning and the encryption of information were also developed and demonstrated.

A multi-responsive organogel and colloid based on the self-assembly of a Ag(i)-azopyridine coordination polymer.

In this work, through the coordination of C3 symmetric azopyridine ligands and Ag(i), coordination polymers with azo groups on the main chain were prepared. The trans coordination polymer formed an organogel with a network of nanofibers at low critical gelation concentrations, and it exhibited the abilities of self-healing and multi-stimuli response to heating, light, mechanical shearing, and chemicals due to the presence of dynamic coordinating bonds. On the other hand, the cis coordination polymer was found to assemble into nanoparticles to give a responsive colloid, which can produce fibrous precipitation in several days upon visible light irradiation due to the isomerization of the azo groups. This work provides a novel example for the design of a multi-responsive organogel and colloid based on the structural transformation of coordination polymers.

A self-healing supramolecular hydrogel with temperature-responsive fluorescence based on an AIE luminogen.

In this work, an AIE luminogen-based hydrogel with temperature-responsive fluorescence was designed and synthesized. The polymeric hydrogel consisted of a supramolecular network through coordination and ionic interactions. When the temperature was decreased, due to the motion restriction of the polyacrylic acid macromolecular segments and the enhancement in ionic interaction, the hydrogel exhibited a blue-shift in the fluorescence emission peak and increase in the fluorescence intensity, resulting in the visualization of fluorescence changes. The hydrogel network benefitted from non-covalent crosslinking and thus possessed self-healing properties at room temperature with good toughness and resiliency. Therefore, this fluorescent supramolecular hydrogel might be used as a temperature-responsive material.

Synthesis and Morphological Control of Biocompatible Fluorescent/Magnetic Janus Nanoparticles Based on the Self-Assembly of Fluorescent Polyurethane and Fe3O4 Nanoparticles.

Functionalized Janus nanoparticles have received increasing interest due to their anisotropic shape and the particular utility in biomedicine areas. In this work, a simple and efficient method was developed to prepare fluorescent/magnetic composite Janus nanoparticles constituted of fluorescent polyurethane and hydrophobic nano Fe3O4. Two kinds of fluorescent polyurethane prepolymers were synthesized by the copolymerization of fluorescent dye monomers, and the fluorescent/magnetic nanoparticles were fabricated in one-pot via the process of mini-emulsification and self-assembly. The nanostructures of the resulting composite nanoparticles, including core/shell and Janus structure, could be controlled by the phase separation in assembly process according to the result of transmission electron microscopy, whereas the amount of the nonpolar segments of polyurethane played an important role in the particle morphology. The prominent magnetic and fluorescent properties of the Janus nanoparticles were also confirmed by vibrating magnetometer and confocal laser scanning microscope. Furthermore, the Janus nanoparticles featured excellent dispersity, storage stability, and cytocompatibility, which might benefit their potential application in biomedical areas.

Metal-Organic Gels Derived from Iron(III) and Pyridine Ligands: Morphology, Self-Healing and Catalysis for Ethylene Selective Dimerization.

Metal-organic gels showing potential application in catalysis have received much concern. In this work, we designed and synthesized two metal-organic gels based on coordination between FeIII and pyridine ligands at room temperature. The gels were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to reveal their assembly structures and morphologies, and it was found the metal-organic gel derived from di-topic ligand was composed of three-dimensional network of nanofibers, while the gel derived from tri-topic ligand was constituted of sponge-like structure with amorphous phase. Rheological analysis showed the gel consisting of nanofiber networks displayed self-healing property. The gels were used as catalysts for selective ethylene dimerization, and the optimum catalysis results of the gel with nanofibers reached the maximal catalytic activity of 1.48×105  g/(mol Fe⋅h) with C4 yield more than 90 %, whereas the sponge-like gel only gave 38 % C4 products at the same condition. The higher dimerization selectivity of the former FeIII gel was attributed to its regular assembly structure and lower steric hindrance of the surface metal sites. Due to its catalytic activity, high selectivity and preparation simplicity, the FeIII gel might be potentially applicable for the preparation of C4 α-olefins.

A metal-organic gel based on Fe(iii) and bi-pyridine ligand for template synthesis of core/shell composite polymer nanowires.

In this study, a novel self-assembled metal-organic gel was synthesized from ferric nitrate and a di-topic ligand, bis(3-pyridyl)terephthalate. The gel consisted of a three dimensional network of uniform nanofibers. The gelation exhibited high selectivity to Fe(iii) based on metal-ligand coordination. The molar ratio of Fe3+ to ligand had a large influence on the assembly process and the morphology of the gel. The metallogel displayed multi-stimuli responsiveness and excellent heat resistance, thus was further applied as a thermo-stable template for the polymerization of N,N'-methylene bisacrylamide to produce the core/shell polymer composite nanowires. Subsequently, the polymer nanotubes were obtained after ammonia post-treatment, comfirming the feasibility of the template synthesis strategy. According to the rheological measurements, the gel-like products of the composite nanowires exhibited better mechanical strength compared to the gel template.

Metallogel template fabrication of pH-responsive copolymer nanowires loaded with silver nanoparticles and their photocatalytic degradation of methylene blue.

Poly(N,N'-methylenebisacrylamide-4-vinylpyridine) (P(MBA-4VP)) nanowires loaded with silver nanoparticles (Ag NPs) have been fabricated by silver metallogel template copolymerization, and subsequently, silver ions are reduced instead of the template being removed. Ag NPs with a diameter of 5-15 nm were dispersed throughout the core of P(MBA-4VP) nanowires. The size and distribution of the formed Ag NPs could be finely controlled by reduction time. The pH sensitivity of P(MBA-4VP) nanowires offers the possibility of Ag NP release from the nanowires under acidic conditions. The photocatalytic performance of the P(MBA-4VP) nanowires loaded with Ag NPs was evaluated for the degradation of methylene blue (MB) under UV light irradiation. Their rate of degradation is dependent on the content and size of the Ag NPs, as well as the pH values of the MB solution. Moreover, the P(MBA-4VP) nanowires loaded with Ag NPs exhibited high photostability, and the photocatalytic efficiency reduced by only 1.81% after being used three times.

Direct transformation of N,N'-methylene bisacrylamide self-assembled fibers into polymer microtubes via RAFT polymerization.

A novel fabrication method of polymer tubes with simple operation process and high yield is presented. N,N'-methylene bisacrylamide (MBA) polymer microtubes are fabricated via reversible addition-fragmentation chain transfer (RAFT) polymerization using MBA self-assembled fibers as both the template and monomer source. The resulting products are characterized by SEM, TEM, FTIR, and element analysis. The mechanical properties of the gel-like product and the MBA organogel are measured by rheometer. The morphology of the polymer tubes obtained via RAFT polymerization is compared with the sample obtained via conventional radical polymerization. Based on the current investigations, the fabrication mechanism of this method is initially proposed.