Nelson L. C. Leung

Aggregation-Induced Emission: Together We Shine, United We Soar!

Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

A mechanistic study of AIE processes of TPE luminogens: intramolecular rotation vs. configurational isomerization

Chromophores containing olefinic double bonds are the core components of many important luminogen systems that show the novel photophysical effect of aggregation-induced emission (AIE). The role and extent of E–Z isomerization (EZI) of the double bond in affecting the solution emissions of the AIE luminogens (AIEgens), however, have not been fully understood. In this work, we verified the occurrence of EZI in the dilute solutions of TPE-cored AIEgens by NMR spectroscopy using elaborate experimental procedures. We further designed a TPE-fluorescein adduct to quantify that EZI plays a minor role whereas intramolecular rotation plays a major role in the emission quenching processes of the AIEgen solutions. This study fills the gap in the research on the restriction of the intramolecular rotation (RIR) mechanism for the AIE effect and provides a useful tool for the mechanistic investigation of photoluminescence processes.

Multiscale Humidity Visualization by Environmentally Sensitive Fluorescent Molecular Rotors

Building humidity sensors possessing the features of diverse-configuration compatibility, and capability of measurement of spatial and temporal humidity gradients is of great interest for highly integrated electronics and wearable monitoring systems. Herein, a visual sensing approach based on fluorescent imaging is presented, by assembling aggregation-induced-emission (AIE)-active molecular rotors into a moisture-captured network; the resulting AIE humidity sensors are compatible with diverse applications, having tunable geometries and desirable architectures. The invisible information of relative humidity (RH) is transformed into different fluorescence colors that enable direct observation by the naked eyes based on the twisted intramolecular charge-transfer effect of the AIE-active molecular rotors. The resulting AIE humidity sensors show excellent performance in terms of good sensitivity, precise quantitative measurement, high spatial-temporal resolution, and fast response/recovery time. Their multiscale applications, such as regional environmental RH detection, internal humidity mapping, and sensitive human-body humidity sensing are demonstrated. The proposed humidity visualization strategy may provide a new insight to develop humidity sensors for various applications.

Probing the dendritic architecture through AIE: challenges and successes

Since the aggregation-induced emission (AIE) phenomenon is very sensitive to steric hindrance, we set out to use it as a tool to probe the periphery of dendrimers. To achieve this, dendrimers with an ethylene oxide (EO) core were synthesized and then decorated with AIE-active units. Tetraphenylethylene (TPE) with varying spacer lengths was used as the AIE decoration to create two parallel series of these dendrimers up to generation four. Systematic photoluminescence studies demonstrated that peripheral crowding starts at G3. Further analysis showed that the AIE technique is sensitive enough to distinguish small differences in architecture. When used in combination with dynamic light scattering, our AIE strategy revealed a complex relationship between the aggregates’ size and their emission.

Facile Multicomponent Polymerizations toward Unconventional Luminescent Polymers with Readily Openable Small Heterocycles

Heterocyclic polymers have gained enormous attention for their unique functionalities and wide applications. In contrast with the well-studied polymer systems with five- or six-membered heterocycles, functional polymers with readily openable small-ring heterocycles have rarely been explored due to their large synthetic difficulty. Herein, a facile one-pot multicomponent polymerization to such polymers is developed. A series of functional polymers with multisubstituted and heteroatom-rich azetidine frameworks are efficiently generated at room temperature in high atom economy from handy monomers. The four-membered azetidine rings in the polymer skeletons can be easily transformed into amide and amidine moieties via a fast and efficient acid-mediated ring-opening reaction, producing brand-new polymeric materials with distinctive properties. All the as-prepared azetidine-containing polymers exhibit intrinsic visible luminescence in the solid state under long-wavelength UV irradiation even without conventionally conjugated structures. Such unconventional luminescence is attributed to the clusteroluminogens formed by through-space electronic interactions of heteroatoms and phenyl rings. All the obtained polymers show excellent optical transparency, high and tunable refractive indices, low optical dispersions and good photopatternability, which make them promising materials in various advanced electronic and optoelectronic devices. The ring-opened polymers can also function as a lysosome-specific fluorescent probe in biological imaging.

A Highly Sensitive Bimodal Detection of Amine Vapours Based on Aggregation Induced Emission of 1,2-Dihydroquinoxaline Derivatives

The detection of food spoilage is a major concern in food safety as large amounts of food are transported globally. Direct analysis of food samples is often time-consuming and requires expensive analytical instrumentation. A much simpler and more cost-effective method for monitoring food fermentation is to detect biogenic amines generated as a by-product during food decomposition. In this work, a series of 1,2-dihydroquinoxaline derivatives (DQs) with aggregation-induced emission (AIE) characteristics were synthesised and their protonated forms, that is, H+ DQs, can be utilised for the sensitive detection of biogenic amines. For example, upon exposure to amine vapours, deprotonation occurs that converts the red-coloured, non-emissive H+ DQ2 back to its yellow-coloured, fluorescent parent form. The bimodal absorption and emission changes endow the system with high sensitivity, capable of detecting ammonia vapour at a concentration of as low as 690 ppb. Taking advantage of this, H+ DQ2 was successfully applied for the detection of food spoilage and was established as a robust and cost effective technique to monitor food safety.