Aggregation-induced emission of siloles

Aggregation-induced emission (AIE) is a unique and significant photophysical phenomenon that differs greatly from the commonly acknowledged aggregation-caused emission quenching observed for many π-conjugated planar chromophores. The mechanistic decipherment of the AIE phenomenon is of high importance for the advance of new AIE systems and exploitation of their potential applications. Propeller-like 2,3,4,5-tetraphenylsiloles are archetypal AIE-active luminogens, and have been adopted as a core part in the design of numerous luminescent materials with diverse functionalities. In this review article, we elucidate the impacts of substituents on the AIE activity and shed light on the structure–property relationship of siloles, with the aim of promoting the judicious design of AIE-active functional materials in the future. Recent representative advances of new silole-based functional materials and their potential applications are reviewed as well.     

Aggregation‐Induced Emission: New Vistas at the Aggregate Level

Aggregation‐induced emission (AIE) describes a photophysical phenomenon in which molecular aggregates exhibit stronger emission than the single molecules. Over the course of the last 20 years, AIE research has made great strides in material development, mechanistic study and high‐tech applications. The achievements of AIE research demonstrate that molecular aggregates show many properties and functions that are absent in molecular species. In this review, we summarize the advances in the field of AIE and its related areas. We specifically focus on the new properties of materials attained by molecular aggregates beyond the microscopic molecular level. We hope this review will inspire more research into molecular ensembles at and beyond the meso level and lead to the significant progress in material and biological science.     

聚集诱导发光机理研究

与传统荧光生色团聚集后导致荧光猝灭相反,有一类化合物在单分子状态下荧光微弱甚至观察不到荧光,而在聚集状态下荧光显著增强,这就是聚集诱导发光(AIE)现象。AIE现象独特的优越性使得众多研究组开发出越来越多的新AIE体系,其机理也被广泛而深入地研究。本文总结了目前为止已经提出的AIE机理,包括分子内旋转受限、分子内共平面、抑制光物理过程或光化学反应、非紧密堆积、形成J-聚集体以及形成特殊激基缔合物等;着重评述了目前研究最为全面、适用范围最广的分子内旋转受限机理。同时介绍了一些基于这些机理设计的新AIE体系。     

AIE Ligand Constructed Zn(Ⅱ)Complex with Reversible Photo-induced Color and Emission Changes

Fluoran salicylaldehyde hydrazone metal complex(FSHMC)is a kind of recently reported photo-responsive system,which has the advantages of simple synthesis,multiple colors as well as distinct color change before and after UV light irradiation.However,the emission property of FSHMC is relatively unitary.In solid state,especially,only fluorescence quench is induced after UV light irradiation,which limits their applications.In this work,a typical aggregation-induced emission(AIE)moiety of tetraphenylethene(TPE)was introduced to the design of FSHMC.The obtained FSHMC,2-Zn,exhibited reversible color and fluorescence changes upon UV light irradiation.Due to the AIE feature of compound 2,2-Zn exhibited different emission changes upon UV light irradiation in THF and in solid matrix,because of the fluorescence resonance energy transfer(FRET)process from TPE moiety to rhodamine B moiety.     

Immobilization of AIEgens into metal‐organic frameworks: Ligand design,emission behavior,and applications

Aggregation‐induced emission (AIE), in which the luminophores are highly emissive in aggregate state, is one of the most unique photophysical phenomena and has shown interesting applications in many areas. The immobilization of AIE luminogens (AIEgens) into metal‐organic frameworks (MOFs), which are inorganic‐organic hybrid porous materials with tunable and predictable structures, has been investigated over the past few years. These well‐defined porous frameworks cannot only provide an ideal platform for studying the mechanism of AIE phenomenon in solid state, but also show potential applications from sensing to white light‐emitting diodes. In this highlight, we will summarize the recent progress of AIEgens‐based MOFs, including ligand design, emission behavior, and applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1809–1817     

Photoinduced Pyramidal Inversion Behavior of Phosphanes Involved with Aggregation-Induced Emission Behavior

Aggregation-induced emission (AIE) is a fascinating phenomenon because of the applications of luminescent materials in the aggregated state, which exploit the large structural changes of the molecules in the excited state. Recently, it was reported that triphenylphosphane derivatives show AIE behavior in which they undergo potentially large structural changes in the excited state. Inspired by this report, photoinduced pyramidal inversion behavior of phosphanes was investigated. In photochemical experiments, the prepared P-stereogenic phosphanes exhibited photoracemization in dilute solution, and a negative correlation was observed between the photoracemization and the AIE phenomenon. Theoretical computations revealed that the inversion barrier in the excited state was much smaller than that in the ground state. This is the first report on the photoinduced pyramidal inversion behavior of phosphanes, which will provide new and unexplored applications.     

Recent Advances in Aggregation-Induced Emission Active Materials for Sensing of Biologically Important Molecules and Drug Delivery System

The emergence and development of aggregation induced emission (AIE) have attracted worldwide attention due to its unique photophysical phenomenon and for removing the obstacle of aggregation-caused quenching (ACQ) which is the most detrimental process thereby making AIE an important and promising aspect in various fields of fluorescent material, sensing, bioimaging, optoelectronics, drug delivery system, and theranostics. In this review, we have discussed insights and explored recent advances that are being made in AIE active materials and their application in sensing, biological cell imaging, and drug delivery systems, and, furthermore, we explored AIE active fluorescent material as a building block in supramolecular chemistry. Herein, we focus on various AIE active molecules such as tetraphenylethylene, AIE-active polymer, quantum dots, AIE active metal-organic framework and triphenylamine, not only in terms of their synthetic routes but also we outline their applications. Finally, we summarize our view of the construction and application of AIE-active molecules, which thus inspiring young researchers to explore new ideas, innovations, and develop the field of supramolecular chemistry in years to come.     

Aggregation‐Induced Emission (AIE): A Historical Perspective

Aggregation‐induced emission (AIE) has attracted considerable interest over the last twenty years. In contrast to the large number of available reviews focusing specifically on AIE, this Essay discusses the AIE phenomenon from a broader perspective, with an emphasis on early observations related to AIE made long before the term was coined. Illustrative examples are highlighted from the 20th century where fluorescence enhancement upon rigidification of dyes in viscous or solid environments or J‐aggregate formation was studied. It is shown that these examples already include typical AIE luminogens such as tetraphenylethylene (TPE) as well as stilbenes and oligo‐ or polyphenylenevinylenes and ‐ethynylenes, which became important fluorescent solid‐state materials in OLED research in the 1990s. Further examples include cyanine dyes such as thiazole orange (TO) or its dimers (TOTOs), which have been widely applied as molecular probes in nucleic acid research. The up to 10 000‐fold fluorescence enhancement of such dyes upon intercalation into double‐stranded DNA, attributable to the restricted intramolecular motion (RIM) concept, afforded commercial products for bioimaging and fluorescence sensing applications already in the early 1990s.     

Self‐Assembly of Aggregation‐Induced‐Emission Molecules

The last decade has witnessed rapid developments in aggregation‐induced emission (AIE). In contrast to traditional aggregation, which causes luminescence quenching (ACQ), AIE is a reverse phenomenon that allows robust luminescence to be retained in aggregated and solid states. This makes it possible to fabricate various highly efficient luminescent materials, which opens new paradigms in a number of fields, such as imaging, sensing, medical therapy, light harvesting, light‐emitting devices, and organic electronic devices. Of the various important features of AIE molecules, their self‐assembly behavior is very attractive because the formation of a well‐defined emissive nanostructure may lead to advanced applications in diverse fields. However, due to the nonplanar topology of AIEgens, it is not easy for them to self‐assemble into well‐defined structures. To date, some strategies have been proposed to achieve the self‐assembly of AIEgens. Herein, we summarize the most recent approaches for the self‐assembly of AIE molecules. These approaches can be sorted into two classes: 1) covalent molecular design and 2) noncovalent supramolecular interactions. We hope this will inspire more excellent work in the field of AIE.     

Aggregation-induced emission

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).     

Bioapplications Manipulated by AIEgens with Nonlinear Optical Effect

The modern medicine requires precise diagnostic techniques while the fluorescent imaging shows great potential in such applications due to its excellent sensitivity and high resolution.However,conducting fluorescent imaging in deep-tissue is not so easy because most luminogens show short-wavelength excitation,which may undergo severe light scattering by the bio-tissue.The marriage of fluorescent imaging with nonlinear optical(NLO)effect can alleviate such adverse effects by utilizing NIR laser to reduce light scattering.On the other hand,scientists are enthusiastic in pursuing luminescent materials,which can match well with NLO application.Aggregation-induced emission(AIE)materials exhibit huge advantages in such aspect not only because of its high luminescent efficiency in aggregate state but also due to its excellent photo-stability(a key factor to meet laser application because of its ultrahigh energy density).Inspired by this,many interesting and meaningful works have sprung up based on AIE luminogens with NLO effect in recent years,and for such reason,it motivates us to summarize them to give a systematic presentation.Here,we first give a brief introduction of the principle of NLO effect.Secondly,the strategies for improving the NLO effect of AIE materials,such as increasing molecular conjugation,introduction of donor-acceptor effect,induction of centrally asymmetric array of AIE molecules in crystals and introduction of intermolecular interactions are clarified.In the final part,we also present the multiple applications of AIEgens with NLO effect in cell imaging,deep-tissue tumor and brain blood vessel imaging and photodynamic therapy.We believe,with this review,the topic will attract more attention from the scientists in multi-science field to accelerate the development of AIE materials in biomedical applications.     

利用Reimer-Tiemann反应合成水杨醛缩肼聚集诱导发光分子的综合实验

聚集诱导发光(Aggregation-Induced Emission,AIE)分子是一类在聚集状态下表现出强烈荧光而在分散状态下荧光较弱甚至无荧光的分子。自2001年首例AIE分子被发现以来,各类新型AIE分子如雨后春笋般相继被开发出来,并在有机光电材料、荧光探针、生物成像等领域表现出非常广泛的应用。其中,水杨醛缩肼就是一类合成简单、荧光强度高的典型AIE分子。本论文介绍了利用Reimer-Tiemann反应合成水杨醛,并通过与水合肼反应进一步得到水杨醛缩肼AIE分子的方法。在本实验中,学生不但练习了经典Reimer-Tiemann反应的操作方法,同时也学习了水杨醛缩肼分子的AIE特性及其产生机理。结合拓展阅读,可使学生进一步了解AIE分子的应用。     

Recent Advances in Mechanism of AIE Mechanochromic Materials

Organic mechanochromic materials(also known as piezochromic materials),whose color or emission changes under mechanical force,have attracted great interest owing to their potential applications in pressure sensors,rewritable materials,optical storage,and security ink.Organic mechanochromic materials with aggregation-induced emission(AIE)features have better development prospects and research value owing to their excellent optical properties.To date,mechanochromism has mostly been realized by means of mechanical grinding.Nevertheless,the magnitude of the grinding force is usually uncontrollable and its direction is anisotropic,making it awkward to study the mechanism of mechanochromic materials.On the contrary,hydrostatic pressure,whose magnitude and direction are controllable,is a more valid and governable method to investigate the mechanism of mechanochromic materials,which can help us to construct a meaningful structure-property relationship and understand the latent origin of the mechanochromism.Furthermore,it is conducive to developing other mechanochromic material systems with desired chemical and physical properties.In this review,we focus on the recent progress in the mechanism of organic mechanochromic materials with AIE features under hydrostatic pressure.Four types of mechanisms are included:intermolecular interaction change,intramolecular conformation change,transformation from locally excited state to intramolecular charge-transfer state,and intra-and inter-molecular effects induced by hydrostatic pressure,respectively.     

Aggregation-induced emission: a coming-of-age ceremony at the age of eighteen

Aggregation-induced emission(AIE) has drawn great attention worldwide for its unique optical phenomenon and huge potential applications. Since coined by Ben Zhong Tang et al. in 2001, AIE has been deeply investigated and widely utilized in many important areas, such as organic light-emitting diode(OLED), sensor, and bio-imaging. Herein, we highlight some important progress of AIE in these eighteen years, including the exploration of internal mechanism and potential applications. Furthermore,some other interestingly emissive behaviors, originating but distinguishing from the AIE concept, are presented. It is anticipated an overall understanding about AIE could be easily caught from this short review for scientists, no matter whether they are involved in this exciting and rising research area or not.     

Progress and trends in self-assembly driven fluorescent organic nanoparticles: A brief overview

Organic nanoparticles have recently attracted increasing attention in diverse field of applications in materials, sensing, biomedicine and others due to their extraordinary physico-optical properties and facile synthesis. These π-conjugated small organic molecules exhibit aggregation induced emission (AIE) property, photo/physical stability, good cytocompatibility as well as biodegradability and easy surface modulation ability. In this mini-review, we have summarized the progress and trends in the area of development of organic nanoparticles from π-conjugated small organic molecule. Some typical as well as few unconventional examples of AIE active systems are discussed and also focussed on their structure-property relationship to exhibit unique photophysical characteristics. To decipher the mechanistic aspect of AIE phenomenon, systematic structural design strategies are also discussed. Finally, development of optoelectronic devices, sensors, bioimaging probes, therapeutic agents, and AIE-active luminogens are exemplified with high tech innovations.     

1+1>2: Fiber Synergy in Aggregation-Induced Emission

Mesoscopic aggregate is important to transfer or even amplify the molecular information in macroscopic materials. As an important branch of aggregate science, aggregation-induced emissive luminogens (AIEgens) often show slight or even no emission in solutions but exhibit bright emission when they aggregate, which open a new avenue for the practical applications. Due to the flexible and rotor structure of AIEgens, the aggregate structure of AIEgens is highly sensitive to the surrounding microenvironment, resulting in adjustable optical properties. Fibers integrated of a multiplicity of functional components are ideal carriers to control the aggregation processes, further assembly of fibers produces large-scale fabrics with amplified functions and practical values. In this Concept article, we focus on the latest advances on the synergy between “AIE+Fiber” for the boosted performance that beyond AIE, and their applications are presented and abstracted out to stimulate new ideas for developing “AIE+Fiber” systems.     

Fluorogenic Thorium Sensors Based on 2,6‐Pyridinedicarboxylic Acid‐Substituted Tetraphenylethenes with Aggregation‐Induced Emission Characteristics

A novel fluorescent sensor based on tetraphenylethene (TPE) modified with 2,6‐pyridinedicarboxylic acid (PDA) that shows aggregation‐induced emission (AIE) characteristics for thorium recognition with remarkable fluoresence enhancement response has been synthesized. This sensor is capable of visually distinguishing Th⁴⁺ among lanthanides, transition metals, and alkali metals under UV light. Th⁴⁺ can be detected by the naked eye at ppb levels owing to the AIE phenomenon. The sensor showed high selectivity for Th⁴⁺ compared to all other metals tested, and this recognition displayed good anti‐interference qualities. This study represents the first application of a AIE fluorescence sensor in actinide metal recognition and it has potential applications in environmental systems for thorium ion detection.     

Recent Advances of AIE-Active Conjugated Polymers: Synthesis and Application

Conjugated polymers (CPs) have long been recognized as an important class of materials. The highly conjugated backbone of the CPs will facilitate the rapid exciton migration and result in amplification of fluorescence signals. However, CPs are likely to aggregate and form excimers in solid states, directly leading to the fluorescence quenching, namely aggregation-caused quenching (ACQ), hence inhibiting their prospective utilizations in a large degree. Since the effect of aggregation-induced emission (AIE) is opposite to that of notorious ACQ, the AIE has raised great attention from scientists. CPs with AIE or aggregation-enhanced emission (AEE) features may help to solve the ACQ problem and meanwhile impart polymers with new properties and practical applications. In this review, we summarize the recent progress on the preparation of CPs with AIE or AEE characteristics, where AIE-active luminogens are located at polymer backbones or pendants. Their potential applications including fluorescent sensors, biological probes, and active layers for the fabrication of light-emitting diodes are also described.     

Highly Luminescent Inks: Aggregation‐Induced Emission of Copper–Iodine Hybrid Clusters

Aggregation‐induced emission (AIE) is an attractive phenomenon in which materials display strong luminescence in the aggregated solid states rather than in the conventional dissolved molecular states. However, highly luminescent inks based on AIE are hard to be obtained because of the difficulty in finely controlling the crystallinity of AIE materials at nanoscale. Herein, we report the preparation of highly luminescent inks via oil‐in‐water microemulsion induced aggregation of Cu–I hybrid clusters based on the highly soluble copper iodide‐tris(3‐methylphenyl)phosphine (Cu₄I₄(P‐(m‐Tol)₃)₄) hybrid. Furthermore, we can synthesize a series of AIE inks with different light‐emission colors to cover the whole visible spectrum range via a facile ligand exchange processes. The assemblies of Cu–I hybrid clusters with AIE characteristics will pave the way to fabricate low‐cost highly luminescent inks.     

Aggregation‐Induced Emission and Aggregation‐Promoted Photo‐oxidation in Thiophene‐Substituted Tetraphenylethylene Derivative

Aggregation‐induced emission combined with aggregation‐promoted photo‐oxidation has been reported only in two works quite recently. In fact, this phenomenon is not commonly observed for AIE‐active molecules. In this work, a new tetraphenylethylene derivative (TPE‐4T) with aggregation‐induced emission (AIE) and aggregation‐promoted photo‐oxidation was synthesized and investigated. The pristine TPE‐4T film exhibits strong bluish‐green emission, which turns to quite weak yellow emission after UV irradiation. Interestingly, after solvent treatment, the weakly fluorescent intermediate will become bright‐yellow emitting. Moreover, the morphology of the TPE‐4T film could be regulated by UV irradiation. The wettability of the TPE‐4T microcrystalline surface is drastically changed from hydrophobic to hydrophilic. This work contributes a new member to the aggregation induced photo‐oxidation family and enriches the photo‐oxidation study of tetraphenylethylene derivatives.