Yuncong Chen

Polyyne bridged AIE luminogens with red emission: design, synthesis, properties and applications

Construction of a donor-acceptor (D-A) structure and extension of π-conjugation are the commonly used strategies to shift the emission of luminophores to the red region. However, molecules with high conjugation and a strong D-A effect tend to show weak emission due to the severe π-π interactions and twisted intramolecular charge transfer (TICT) effects. The turn-on characteristic of AIE luminogens (AIEgens) will also be lost due to the conjugation-enhanced emission in the solution state. Herein, a polyyne-bridged AIE luminogen (2TPE-4E) with long wavelength absorption and red emission has been afforded. Despite its large π-conjugation, 2TPE-4E suffers from no emission quenching resulted from strong π-π interactions and twisted intramolecular charge transfer effects. The strong red emission and the high photostability of 2TPE-4E inspired us to use it for targeted-imaging of cancer cells and monitoring the receptor mediated endocytosis process.

An Easily Accessible Ionic Aggregation‐Induced Emission Luminogen with Hydrogen‐Bonding‐Switchable Emission and Wash‐Free Imaging Ability

Ionic fluorophores are powerful tools for the study of environmental science and bio-imaging. However, traditional ionic dyes usually require long synthetic steps and suffer from a quenching effect caused by aggregation. A water-soluble ionic aggregation-induced emission luminogen called DBTA is presented, which is readily accessed by a one-step reaction. The switchable emission manipulated by hydrogen bonding provided solid evidence for the restriction of intramolecular motions as the mechanism of aggregation-induced emission. DBTA can not only differentiate solvents with different H-bond donor acidities but also capable of wash-free imaging in living HeLa cells and fish larva.

Monitoring and quantification of the complex bioaccumulation process of mercury ion in algae by a novel aggregation-induced emission fluorogen

In this study, a novel methodology was developed using a specified aggregation-induced emission fluorogen (AIEgen) to monitor and quantify the complex bioaccumulation process in a microcosm aquatic ecosystem. Mercury ion (Hg2+) was used as the pollutant and Euglena gracilis as a representative algal species in water, to develop this new methodology for understanding the processes of bioaccumulation and biorelease of a heavy metal in algae. AIEgen can easily detect Hg2+ in the environment by the “turn-on” feature, and a relationship was built among photoluminescence (PL) intensity, AIEgen concentration, and Hg2+ concentration. The AIEgen was effectively used for quantifying Hg2+ concentration in the bioaccumulation process by reading the PL intensity of the solution. Bioaccumulation, bioaccumulation efficiency, and the ratio of Hg2+ in Euglena gracilis cells and the environment were carefully characterized by this novel method and the results were further validated with the existing well-established analytical method. The quantitative detection of Hg2+ absorption and release from the algae by the AIEgen demonstrates a novel, green, and sustainable approach to understand the dynamics of Hg2+ between aquatic organisms and the environment.

The unusual aggregation-induced emission of coplanar organoboron isomers and their lipid droplet-specific applications

Luminogens with aggregation-induced emission (AIE) characteristics generally possess twisted structures to prevent emission quenching in the solid state by π–π stacking interactions. In this work, new organoboron derivatives with coplanar structures were synthesized and found to be AIE-active. Analysis by photoluminescence spectroscopy, single crystal X-ray diffraction and theoretical calculations depicted that the distinct luminescence behaviors of the molecules stemmed from the different extent of excited-state double-bond reorganization (ESDBR), which consumed the energy of the excitons through non-radiative pathways. This process was restricted in a highly viscous medium or in the solid state to enable the molecules to emit efficiently. The organoboron derivatives based on the ESDBR mechanism not only provide a new strategy to design coplanar AIE luminogens but also act as biological probes excellently and specifically targeting lipid droplets.

Bright Near-Infrared Aggregation-Induced Emission Luminogens with Strong Two-Photon Absorption, Excellent Organelle Specificity, and Efficient Photodynamic Therapy Potential

Far-red and near-infrared (NIR) fluorescent materials possessing the characteristics of strong two-photon absorption and aggregation-induced emission (AIE) as well as specific targeting capability are much-sought-after for bioimaging and therapeutic applications due to their deep penetration depth and high resolution. Herein, a series of dipolar far-red and NIR AIE luminogens with a strong push-pull effect are designed and synthesized. The obtained fluorophores display bright far-red and NIR solid-state fluorescence with a high quantum yield of up to 30%, large Stokes shifts of up to 244 nm, and large two-photon absorption cross-sections of up to 887 GM. A total of three neutral AIEgens show specific lipid droplet (LD)-targeting capability, while the one with cationic and lipophilic characteristics tends to target the mitochondria specifically. All of the molecules demonstrate good biocompatibility, high brightness, and superior photostability. They also serve as efficient two-photon fluorescence-imaging agents for the clear visualization of LDs or mitochondria in living cells and tissues with deep tissue penetration (up to 150 μm) and high contrast. These AIEgens can efficiently generate singlet oxygen upon light irradiation for the photodynamic ablation of cancer cells. All of these intriguing results prove that these far-red and NIR AIEgens are excellent candidates for the two-photon fluorescence imaging of LDs or mitochondria and organelle-targeting photodynamic cancer therapy.

Quantitative evaluation and in vivo visualization of mercury ion bioaccumulation in rotifers by novel aggregation-induced emission fluorogen nanoparticles

In this study, a specifically-designed aggregation-induced emission fluorogen (AIEgen) with nanoparticle aggregates was used to quantitatively evaluate the bioaccumulation of Hg2+ and visualize Hg2+ kinetics in vivo within the rotifer Brachionus plicatilis for the first time. Quantitative results showed that a sharp drop in Hg2+ concentration occurred at the very beginning in the medium containing rotifers and Hg2+, showing a quick initial uptake of Hg2+ by the rotifers, and then the concentration in the medium plateaued after 5 min. With an increase in rotifer density, the amount of bioaccumulation increased in the rotifer. However, the bioaccumulation efficiency of Hg2+ decreased from 5.28 μg mg−1 h−1 at a low rotifer density of 0.093 mg ml−1 to 2.61 μg mg−1 h−1 at a high rotifer density of 0.375 mg mL−1. Moreover, the fluorescence images and spectra results illustrate that the ingestion of Hg2+ by the rotifer was via its mouth surrounded by the ciliary corona to the digestive tract, and Hg2+ could not permeate into the body integument through diffusion during the study period. Hg2+-induced fluorescence in rotifers dissipated in 6 h after staining, possibly through defecation and excretion. This study indicates that inorganic mercury can be quickly ingested by a rotifer via feeding, but is unlikely deposited as methylated mercury in rotifer tissues.