Bringing Inherent Charges into Aggregation-Induced Emission Research

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Charged organic molecules, such as DNA, RNA, proteins, and polysaccharides, are ubiquitous and indispensable in natural living systems, which possess specific biological functions to interact with oppositely charged species via electrostatic attraction.The molecules with inherent charges typically differentiate themselves from the neutral ones with unique attributes (e.g., ionic interactions and high polarity), thereby playing a pivotal role in a broad spectrum of areas, including supramolecular chemistry, structural biology, and materials science. It is thus of great importance to explore and develop various charged organic systems for biomimicry and the creation of functional materials. In 2001, our group reported a peculiar luminogen that exhibited weak emission in solution but had significantly enhanced emission in aggregates, and we, for the first time, coined this phenomenon as aggregation-induced emission (AIE). The AIE concept significantly changes the cognition of the scientific community toward classic photophysical phenomena. Since the discovery of this unusual luminescence phenomenon, AIE luminogens (AIEgens) have attracted extensive attention from researchers in a plethora of disciplines because of their high brightness in aggregates, large Stokes shift, excellent photostability, and good biocompatibility. In the past 10 years, our laboratory has expended a great amount of effort to bring inherent charges into AIE research and acquired fruitful achievements.In this Account, we summarize the progress of charged AIE systems primarily made by our laboratory. We start with a brief introduction to charged AIEgens and then discuss their design strategies from molecular and topological perspectives, respectively. Next, we review the unique properties of charged AIEgens, including D−A interactions, anion−π + interactions, and intermolecular electrostatic interactions, with an emphasis on how they differentiate themselves from the neutral analogs. On the one hand, positively charged AIEgens exhibit unique photophysical properties by forming typical donor−acceptor structures to manipulate the emission wavelength or initiate ultralong persistent luminescence. On the other hand, positively charged AIEgens exhibit unique physiochemical properties, such as an adjustable targeting capability toward biological targets and a strong capability for the generation of reactive oxygen species. Furthermore, we showcase the applications of charged AIEgens in imaging and diagnosis, photodynamic therapy, gas separation, and solar desalination. Finally, we conclude this Account with a summary and some perspectives regarding the existing challenges and future directions. We hope that this Account can spark new ideas and inspire scientists from different disciplines to explore this nascent yet promising research area.

Peptide‐Engineered AIE Nanofibers with Excellent and Precisely Adjustable Antibacterial Activity

“…There were even some very large clusters with countless bacteria in the NFs-K18 group, and the size of these clusters reached approximately 30 µm (Figure S9, Supporting Information, which was not counted in Figure 2c,d), further demonstrating the strong aggregating ability of NFs-K18 to bacteria. Until now, most antibacterial AIEgens with photodynamic activity reported in the literature have only focused on their intrinsic aggregation-enhanced ROS generation behavior, [39,40] but the ability to induce the aggregation of bacteria has been much less studied. [41][42][43] Herein, the simultaneous induction of AIEgen and bacterial aggregation undoubtedly provides a new avenue to improve the photodynamic killing efficiency for the treatment of bacterial infection.…”

Ion−π interactions for constructing organic luminescent materials

“…[ 13 ] However, the luminescence performances of these organic materials are always greatly discounted due to the detrimental π−π interactions, which resulted in serious quenching of their luminescence in the aggregated or solid states, or after they accumulated insides cells. [ 14–17 ] Tremendous efforts based on the formation of J −aggregates [ 18–19 ] or the introduction of large steric groups and noncovalent interactions (hydrogen bonding, halogen bonding, C−H···π, and ion−π interactions, etc.) [ 20–22 ] have been taken to replace the extensive π−π interactions and thus to circurmvent the luminescence quenching problem.…”

Polarity-Sensitive Fluorescent Probe for Reflecting the Packing Degree of Bacterial Membrane Lipids

“…As a result, the development of a polarity-sensitive probe is potentially feasible to identify such a minute difference. Among various chemical probes, the fluorescent ones are intrinsically advantageous in biosensing due to their noninvasiveness, high sensitivity, real-time feedback, and high spatial resolution. − Although various fluorescent probes have been reported for bacterial membrane studies, none of them are intentionally designed for reflecting the packing degree of bacterial membrane lipids (Table S1). In view of the unique responsiveness to environmental polarity and the molecular state of aggregation, organic luminogens with both twist intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) properties are promising to fulfill this challenging task.…”