Institute of Molecular Functional Materials

Aggregation-induced emission (AIE) is another photophysical phenomenon associated with chromophore aggregation. The concept of AIE has been introduced by a group of researchers in 2001. In the AIE process, non-emissive luminogens are induced to emit by the aggregate formation. The luminogens exhibiting AIE attributes are termed AIEgens, by analogue with the term of 'mesogens' for the molecules showing mesomorphism under suitable conditions.

Luminogenic materials with aggregation-induced emission (AIE) attributes have attracted much interest since the debut of the AIE concept in 2001. In this critical review, recent progress in the area of AIE research is summarized. Typical examples of AIE systems are discussed, from which their structure-property relationships are derived. Through mechanistic decipherment of the photophysical processes, structural design strategies for generating new AIE luminogens are developed. Technological, especially optoelectronic and biological, applications of the AIE systems are exemplified to illustrate how the novel AIE effect can be utilized for high-tech innovations (183 references).

"United we stand, divided we fall."--Aesop. Aggregation-induced emission (AIE) refers to a photophysical phenomenon shown by a group of luminogenic materials that are non-emissive when they are dissolved in good solvents as molecules but become highly luminescent when they are clustered in poor solvents or solid state as aggregates. In this Review we summarize the recent progresses made in the area of AIE research. We conduct mechanistic analyses of the AIE processes, unify the restriction of intramolecular motions (RIM) as the main cause for the AIE effects, and derive RIM-based molecular engineering strategies for the design of new AIE luminogens (AIEgens). Typical examples of the newly developed AIEgens and their high-tech applications as optoelectronic materials, chemical sensors and biomedical probes are presented and discussed.

Simultaneous enhancement of open-circuit voltage, short-circuit current density, and fill factor in highly efficient polymer solar cells by incorporating an alcohol/water-soluble conjugated polymer as cathode interlayer is domonstrated. When combined with a low-bandgap polymer PTB7 as the electron donor material, the power efficiency of the devices is improved to certified 8.370%. Due to drastic improvement in efficiency and easy utilization, this method opens new opportunities for PSCs from various material systems to improve towards 10% efficiency. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Fluorescent bioprobes are powerful tools for analytical sensing and optical imaging, which allow direct visualization of biological analytes at the molecular level and offer useful insights into complex biological structures and processes. The sensing and imaging sensitivity of a bioprobe is determined by the brightness and contrast of its fluorescence before and after analyte binding. Emission from a fluorophore is often quenched at high concentration or in aggregate state, which is notoriously known as concentration quenching or aggregation-caused quenching (ACQ). The ACQ effect limits the label-to-analyte ratio and forces researchers to use very dilute solutions of fluorophores. It compels many probes to operate in a fluorescence "turn-off" mode with a narrow scope of practical applications. The unique aggregation-induced emission (AIE) process offers a straightforward solution to the ACQ problem. Typical AIE fluorogens are characterized by their propeller-shaped rotorlike structures, which undergo low-frequency torsional motions as isolated molecules and emit very weakly in solutions. Their aggregates show strong fluorescence mainly due to the restriction of their intramolecular rotations in the aggregate state. This fascinating attribute of AIE fluorogens provides a new platform for the development of fluorescence light-up molecules and photostable nanoaggregates for specific analyte detection and imaging. In this Account, we review our recent AIE work to highlight the utility of AIE effect in the development of new fluorescent bioprobes, which allows the use of highly concentrated fluorogens for biosensing and imaging. The simple design and fluorescence turn-on feature of the molecular AIE bioprobes offer direct visualization of specific analytes and biological processes in aqueous media with higher sensitivity and better accuracy than traditional fluorescence turn-off probes. The AIE dot-based bioprobes with different formulations and surface functionalities show advanced features over quantum dots and small molecule dyes, such as large absorptivity, high luminosity, excellent biocompatibility, free of random blinking, and strong photobleaching resistance. These features enable cancer cell detection, long term cell tracing, and tumor imaging in a noninvasive and high contrast manner. Recent research has significantly expanded the scope of biological applications of AIE fluorogens and offers new strategies to fluorescent bioprobe design. We anticipate that future development on AIE bioprobes will combine one- or multiphoton fluorescence with other modalities (e.g., magnetic resonance imaging) or functionalities (e.g. therapy) to fully demonstrate their potential as a new generation of theranostic reagent. In parallel, the advances in molecular biology will provide more specific bioreceptors, which will enable the development of next generation AIE bioprobes with high selectivity and sensitivity for molecular sensing and imaging.

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTLight-Emitting Self-Assembled Materials Based on d8 and d10 Transition Metal ComplexesVivian Wing-Wah Yam*, Vonika Ka-Man Au, and Sammual Yu-Lut LeungView Author Information Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants Committee (Hong Kong)) and Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China*E-mail: [email protected]Cite this: Chem. Rev. 2015, 115, 15, 7589–7728Publication Date (Web):July 9, 2015Publication History Received5 February 2015Published online9 July 2015Published inissue 12 August 2015https://pubs.acs.org/doi/10.1021/acs.chemrev.5b00074https://doi.org/10.1021/acs.chemrev.5b00074review-articleACS PublicationsCopyright © 2015 American Chemical SocietyRequest reuse permissionsArticle Views23994Altmetric-Citations1311LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Crystal structure,Excited states,Gold,Ligands,Luminescence Get e-Alerts

From its initial use to describe hydrolysis and condensation processes, the term ‘sol–gel’ is now used for a diverse range of chemistries.

Macromolecules with aggregation-induced emission (AIE) attributes are a class of luminescent materials that display enhanced emission when they are aggregated. They have attracted much attention because of their good solubility, processability, high emission efficiency in the aggregated states, etc. A large variety of AIE macromolecules have been developed, showing exponential growth of research interest in this field. This review summarizes the design principles and recent synthetic advancements, topological structures, as well as the frontiers of functionalities and potential applications of AIE macromolecules, especially fluorescence sensing, biological applications and optoelectronic applications, with an emphasis on the recent progress. New luminogenic systems without conventional chromophores displaying aggregated state emission are discussed. The highly dense clusters of heteroatoms with lone pair electrons in these systems may serve as the chromophore and are cited as "heterodox clusters". It is expected that the mechanistic insights into the AIE phenomena, based on the restriction of intramolecular motions and structure rigidification, can guide the future design of AIE materials with fascinating structures and functionalities.

In this review, the fundamental, current status and challenges of different types of HER electrocatalysts are highlighted.

Transition metal nitrides (TMNs), by virtue of their unique electronic structure, high electrical conductivity, superior chemical stability, and excellent mechanical robustness, have triggered tremendous research interest over the past decade, and showed great potential for electrochemical energy conversion and storage. However, bulk TMNs usually suffer from limited numbers of active sites and sluggish ionic kinetics, and eventually ordinary electrochemical performance. Designing nanostructured TMNs with tailored morphology and good dispersity has proved an effective strategy to address these issues, which provides a larger specific surface area, more abundant active sites, and shorter ion and mass transport distances over the bulk counterparts. Herein, the most up-to-date progress on TMN-based nanomaterials is comprehensively reviewed, focusing on geometric-structure design, electronic-structure engineering, and applications in electrochemical energy conversion and storage, including electrocatalysis, supercapacitors, and rechargeable batteries. Finally, we outline the future challenges of TMN-based nanomaterials and their possible research directions beyond electrochemical energy applications.

Efficient solid-state emitters developed by a new approach are described. While emission from triphenylamine (TPA) and its dimer (DTPA) is weakened by aggregation, attaching tetraphenylethene (TPE) units to the amines boosts their emission efficiencies up to 100% in the aggregate state without harming their hole-transport properties. The resultant 3TPETPA and 4TPEDTPA luminogens show excellent electroluminescence performance. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Luminescent materials with efficient solid-state emissions are important for the advancement of optoelectronics. Recently, a new class of propeller-like luminogenic molecules with aggregation-induced emission (AIE) characteristics has drawn increasing research interest. Among them, tetraphenylethene (TPE) is an archetypal luminogen with a simple molecule structure but shows a splendid AIE effect. Utilizing TPE as a building block, an effective strategy to create efficient solid-state emitters is developed. In this feature article, we review mainly our recent work on the construction of luminogenic materials from TPE and present their applications in organic light-emitting diodes. The applicability of the synthetic strategy and the utility of the resulting materials are demonstrated.

Abstract The development of single molecule white light emitters is extremely challenging for pure phosphorescent metal-free system at room temperature. Here we report a single pure organic phosphor, namely 4-chlorobenzoyldibenzothiophene, emitting white room temperature phosphorescence with Commission Internationale de l’Éclair-age coordinates of (0.33, 0.35). Experimental and theoretical investigations reveal that the white light emission is emerged from dual phosphorescence, which emit from the first and second excited triplet states. We also demonstrate the validity of the strategy to achieve metal-free pure phosphorescent single molecule white light emitters by intrasystem mixing dual room temperature phosphorescence arising from the low- and high-lying triplet states.

Aggregation-induced emission (AIE) has been harnessed in many systems through the principle of restriction of intramolecular rotations (RIR) based on mechanistic understanding from archetypal AIE molecules such as tetraphenylethene (TPE). However, as the family of AIE-active molecules grows, the RIR model cannot fully explain some AIE phenomena. Here, we report a broadening of the AIE mechanism through analysis of 10,10',11,11'-tetrahydro-5,5'-bidibenzo[a,d][7]annulenylidene (THBDBA), and 5,5'-bidibenzo[a,d][7]annulenylidene (BDBA). Analyses of the computational QM/MM model reveal that the novel mechanism behind the AIE of THBDBA and BDBA is the restriction of intramolecular vibration (RIV). A more generalized mechanistic understanding of AIE results by combining RIR and RIV into the principle of restriction of intramolecular motions (RIM).

Driven by the high demand for sensitive and specific tools for optical sensing and imaging, bioprobes with various working mechanisms and advanced functionalities are flourishing at an incredible speed. Conventional fluorescent probes suffer from the notorious effect of aggregation-caused quenching that imposes limitation on their labelling efficiency or concentration to achieve desired sensitivity. The recently emerged fluorogens with an aggregation-induced emission (AIE) feature offer a timely remedy to tackle the challenge. Utilizing the unique properties of AIE fluorogens (AIEgens), specific light-up probes have been constructed through functionalization with recognition elements, showing advantages such as low background interference, a high signal to noise ratio and superior photostability with activatable therapeutic effects. In this tutorial review, we summarize the recent progress in the development of specific AIEgen-based light-up bioprobes. Through illustration of their operation mechanisms and application examples, we hope to provide guidelines for the design of more advanced AIE sensing and imaging platforms with high selectivity, great sensitivity and wide adaptability to a broad range of biomedical applications.

Tracking the dynamics of mitochondrial morphology has attracted much research interest because of its involvement in early stage apoptosis and degenerative conditions. To follow this process, highly specific and photostable fluorescent probes are in demand. Commercially available mitochondria trackers, however, suffer from poor photostability. To overcome this limitation, we have designed and synthesized a fluorescent agent, tetraphenylethene-triphenylphosphonium (TPE-TPP), for mitochondrial imaging. Inherent from the mitochondrial-targeting ability of TPP groups and the aggregation-induced emission (AIE) characteristics of the TPE core, TPE-TPP possesses high specificity to mitochondria, superior photostability, and appreciable tolerance to environmental change, allowing imaging and tracking of the mitochondrial morphological changes in a long period of time.

We report a 2D layered metal–organic framework (MOF) with wide channels named NUS-1 and its activated analogue NUS-1a composed of Zn4O-like secondary building units and tetraphenylethene (TPE)-based ligand 4,4′-(2,2-diphenylethene-1,1-diyl)dibenzoic acid. Due to its special structure, NUS-1a exhibits unprecedented gas sorption behavior, glass-transition-like phase transition under cryogenic conditions, and responsive turn-on fluorescence to various volatile organic compounds. Our approach using angular ligand containing partially fixed TPE units paves a way toward highly porous MOFs with fluorescence turn-on response that will find wide applications in chemical sensing.

The thermochromic and mechanochromic fluorescence of diphenyldibenzofulvenes is investigated. Emission is boosted and blue-shifted upon crystallization. Yellow emissive crystals of the material transform to green fluorescent crystals upon heating before melting. Reversible switching of the emission color and efficiency are achieved by repeated amorphization and crystallization of dye molecules by a pure thermal process or grinding–heating cycles.

The invention of the scanning tunneling microscope has led to the visualization of molecules in real space on atomically flat conductive substrates. This has boosted research into supramolecular chemistry on surfaces. In this Review, we highlight recent developments in the design and functionality of supramolecular surface patterns, with special attention paid to those networks which are chiral or contain a high degree of porosity as well as to the reactivity, which is one of the most important recent developments in supramolecular surface chemistry.

Amongst the areas of supramolecular chemistry, low molecular weight gelators (supramolecular gels) have been considered to be one of the most interesting soft and smart materials due to their ability to construct polymeric structures from small molecules through non-covalent interactions. Recently, metal centres have been incorporated into organic-based gelators that can integrate the interesting and unique properties of metal complexes into gelator molecules that can hardly be achieved by pure organic compounds. In this review, we will give a summary of the recent developments on metallogels and their interesting properties originating from the metal centres.