Aggregation-Induced Emission in Organic Nanoparticles: Properties and Applications: a Review

Aggregation-Induced Emission-Active Nanostructures: Beyond Biomedical Applications

The discovery of aggregation-induced emission (AIE) phenomenon in 2001 has had a significant impact on materials development across different research disciplines. AIE-active materials have been widely exploited for various applications in optoelectronics, sensing, biomedical, and stimuli-responsive systems, etc. This is made possible by integrating AIE features with other fields of science and engineering, such as nanoscience and nanotechnology. AIE has been extensively employed, particularly for biomedical applications, such as biosensing, bioimaging, and theranostics. However, development of AIE-based nanotechnology for other applications is comparatively less, although there have been increasing research activities in recent years. Given the significance and potential of the marriage between AIE hallmark and nanotechnology in AIE-active materials development, this review article summarizes and showcases the latest research efforts in AIE-based nanomaterials, including nanomaterials synthesis and their nonbiomedical applications, such as sensing, optoelectronics, functional coatings, and stimuli-responsive systems. A perspective on the outlook of AIE-based nanostructured materials and relevant nanotechnology for nonbiomedical applications will be provided, giving an insight into how to design AIE-active nanostructures as well as their applications beyond the biomedical domain.

Coassembly of Fiber Hydrogel with Antibacterial Activity for Wound Healing

Wound healing remains a critical challenge due to its vulnerability to bacterial infection and the complicated inflammatory microenvironment. Herein, we report a novel antibacterial hydrogel constructed only by gallic acid (GA) and phycocyanin (PC), which is expected for the treatment of bacteria-infected wounds. These GA/PC hydrogels (GP) was found to coassemble into fibrous networks with a diameter of around 2 μm mainly through noncovalent interactions of hydrogen bonds, van der Waals force, and π interaction. Notably, these GP hydrogels showed excellent rheological properties (i.e., storage modulus of more than 9.0 × 10⁴ Pa) and outstanding biocompatibility and antibacterial activities. Thanks to the incorporation of GA and PC, the GP hydrogels enabled adherence to the moist wound tissue and achieved a sustained release of GA and PC into the wound skin, therefore effectively attenuating inflammation and accelerating wound healing both in normal mice and bacteria-infected mice through regulating the expression of the tight junction protein and the alleviation of oxidative stress. Considering these results, these GP hydrogels are demonstrated to be a promising candidate for bacteria-infected wound healing.

Yellow to blue switching of fluorescence by the tuning of the pentaphenylphosphole structure: phosphorus electronic state vs. ring conjugation

The interaction between diphenylacetylene and dichlorophenylphosphine under various conditions is a simple method for the preparation of pentaphenylphosphole derivatives exhibiting fluorescence properties. Depending on the electronic state of the various centers of the phospholic structure, it was possible to obtain molecules with fluorescence, as in the blue area for 1,2,3,4,5-pentaphenyl-2,5-dihydro-phosphole-1-oxide (H₂PPPO), in the yellow area for 1,2,3,4,5-pentaphenylphosphole-1-oxide (PPPO) and in the cyan area for 1,2,3,4,5-pentaphenylphosphole (PPP). The effect of the structure and π-conjugation on the optical properties of these compounds was studied using PPP derivatives as examples. Unusual changes in the optical properties of PPP derivatives in solution and in the crystalline state are explained. In the case of agglomeration of PPPO and PPP molecules, the effect of aggregation-induced emission (AIE) was observed to have weak fluorescence in solution and strong fluorescence in the aggregated state. However, for H₂PPPO, the AIE effect remains mild. With the help of experimental studies, supported by theoretical calculations, the main mechanism of the optical properties of pentaphenylphosphole derivatives has been revealed. It was observed that the intramolecular motions of PPPO and PPP are more limited in the solid state than the motions of H₂PPPO, which is associated with less conjugation of the phenyl rotors of H₂PPPO. The analysis of the structure and distribution of electron density showed why hydrogenation of the phosphole ring leads to a sharp change in the optical properties of pentaphenylphosphole derivatives, while the oxidation of phosphorus does not lead to the disappearance of the AIE effect and to a lesser extent affects the change in the fluorescence wavelength. Thus, it was shown how the regulation of various structural features of the phospholic ring helps to control the optical properties of such compounds.

Highly Selective and Sensitive Aggregation-Induced Emission of Fluorescein-Coated Metal Oxide Nanoparticles

We report the synthesis, characterization, and photophysical properties of novel metal oxide nanoparticles (NPs) coated with specially designed fluorescein substituents which are capped with electron-withdrawing groups. The fluorescein-coated nanoparticles were synthesized in excellent yields, and their structures were confirmed using various advanced spectroscopic, instrumental, and surface analysis techniques, revealing the formation of the target functionalized nanoparticles (FNPs) which show superior chemical and thermal stabilities. In addition, the photophysical properties of the FNPs were examined using UV-visible absorption and fluorescence spectroscopy. These latter techniques disclosed aggregation-induced emission (AIE) properties for most of the target FNPs, namely those which are soluble in common organic solvents at selective concentration ranges of water fractions in the solvent mixture.