Tetraphenylethene-based highly emissive fluorescent molecules with aggregation-induced emission (AIE) and various mechanofluorochromic characteristics

Three tetraphenylethene-based compounds with different substituents were successfully synthesized. All these fluorescent molecules exhibited typical aggregation-induced emission (AIE) effect. In addition, these luminogens showed various mechanochromic luminescence phenomena. Moreover, the mechanofluorochromic behavior of luminogen 1 was self-reversible.     

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.     

压致变色聚集诱导发光材料

聚集诱导发光化合物分子具有特殊的螺旋桨形扭曲构象结构, 导致其很难在结晶状态下进行紧密堆砌, 使得其结晶结构容易在外力的作用发生改变, 致使其分子能级水平和发光光谱发生变化, 产生压致发光变色现象. 因此, 聚集诱导发光化合物是压致发光变色材料的一个重要来源. 压致变色聚集诱导发光材料是一类重要的压致发光变色材料, 其既具有压致发光变色的性能, 又具有聚集诱导发光的性能. 它是一类智能材料, 在应力传感、商标防伪和发光器件等领域具有重要的潜在应用, 近年来受到人们极大的关注. 本文分类介绍了近年来压致变色聚集诱导发光材料的研究进展.     

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).     

Synthesis, two-photon absorption and AIE properties of multibranched thiophene-based triphenylamine derivatives with triazine core

Two new multibranched thiophene-based triarylamine derivatives with 1,3,5-triazine core are synthesized and characterized. Their one-and two-photon absorption properties and aggregation-induced emission effect have been investigated. Both the STAPA-based compounds are AIE active. The two-photon absorption (2PA) cross sections measured by the open aperture Z-scan technique are determined to be 620 and 1610 GM for STAPA-a and STAPA-b in chloroform,respectively, which dramatically increase with the introduction of alkyl chains. The relationship between their structures and properties on one-and two-photon absorption and aggregation-induced emission is discussed, which allows us to examine the effect of introducing alkyl chains. In addition, solvent effects also show a significant influence on the 2PA cross section. The two compounds with excellent AIE and 2PA properties provide attractive alternatives for the biophotonic materials.     

Three-dimensional organic cage with aggregation-induced delayed fluorescence

A new kind of emissive small-molecular organic cage has been developed via the combination of coupling and condensation reactions,which shows outstanding solubility,structural stability and potential spatial isomeric chirality.Interestingly,through the introduction of proper donor and acceptor units,this emissive organic cage is the first among organic cages to exhibit red aggregation-induced delayed fluorescence with photoluminescence emission at 603 nm.The finding not only expands the types of emissive small-molecular organic cages,but also represents an important step for further development of red delayed fluorescence materials with good solubility and aggregation-induced emission feature.     

外缘烷基链长对共轭有机小分子聚集行为及光电性质影响

改变分子化学结构和调控分子结构聚集态行为从而影响或改变材料的化学和物理性质, 是开发新型高效有机光电功能材料的重要手段. 在共轭有机分子外缘引入烷基链一般是为了改进材料溶解性能, 但近来的一些研究表明, 烷基链长对一些共轭有机小分子固态聚集行为和光电性质具有重要影响, 烷基链扮演着显著调控材料光电性质的“功能基团”作用. 本文以聚集诱导发光（aggregation-induced emission, AIE）/聚集强化荧光（aggregation enhanced emission, AEE）发射共轭有机小分子为重点, 对近年来有关烷基链长对共轭有机分子聚集形态和光电性质影响的一些典型事例进行评述, 旨在使人们在进行共轭有机分子设计合成及其结构与性能关系研究中能够关注烷基链的因素, 使烷基链变化作为功能导向晶态共轭有机材料设计合成及其可控制备的一种手段.     

Aggregation-induced emission enhancement (AIEE)-active mechanofluorochromic tetraphenylethene derivative bearing a rhodamine unit

A novel tetraphenylethene derivative with a rhodamine unit was successfully synthesized via high-efficiency Suzuki coupling reaction. The highly solid-state emissive target fluorescent molecule exhibited significative aggregation-induced emission enhancement (AIEE) feature. Furthermore, the luminogen showed reversible mechanochromic luminescence behavior involving color change from orange to red. In addition, the powder X-ray diffraction (XRD) test results verified that the mechanofluorochromic phenomenon of luminogen 1 was attributed to a morphological transformation between the crystalline and amorphous states.     

Optical waveguides at micro/nanoscale based on functional small organic molecules

Optical waveguides synthesized at the micro/nanoscale have drawn great interest for their potential applications in high speed miniaturized photonic integrations. In this Perspective article, we mainly focus on the related works on active optical waveguides based on functional small organic molecules in micro/nano regime. We begin with a general overview of recent progress in sub-wavelength optical waveguides, including the development of waveguide materials of inorganic semiconductors, polymers, and small organic molecules. Then brief highlights are put on the recently reported organic optical waveguides with various unique optical properties induced by the ordered molecular aggregations in the micro/nano-sized solid-state structures, such as polarized emission, lasing, aggregation-induced enhanced emission, etc. This article concludes with a summary and our personal view about the direction of future development in organic opto-functional waveguides as photonic devices.     

Mechanofluorochromic behavior of anthracene-based acylhydrazone derivatives

Two anthracene-based derivatives, having one or two acylhydrazone branches attached on the anthracene, namely, asymmetrical AHP-1 and symmetrical AHBP-1 were designed. These compounds exhibited mechanofluorochromic behavior with the emission colors reversibly changing upon grinding and recrystallizing. The mechanofluorochromic mechanism was explored and ascribed to the crystalline-amorphous phase transformation. In addition, the red-shifted extent of fluorescent emission of the ground AHBP-1 samples was more than that of AHP-1.     

Recent Progress in the Development of Solid-State Luminescent o-Carboranes with Stimuli Responsivity

o-Carborane, a cluster compound containing boron and adjacent carbon atoms, displays intriguing luminescent properties. Recently, compounds containing o-carborane units were found to show suppressed aggregation-induced quenching and intense solid-state emission; they also show potential for the development of stimuli-responsive luminochromic materials. In this Minireview, we introduce three kinds of fundamental photochemical properties: aggregation-induced emission, twisted intramolecular charge transfer in crystals, and environment-sensitive excimer formation in solids. Based on these properties, several types of luminochromism, such as thermos-, vapo-, and mechanochromism, have been discovered. Based mainly on results from recent studies, we illustrate these mechanisms as well as unique luminescent behaviors of o-carborane derivatives.     

Photophysical Switching between Aggregation-Induced Phosphorescence and Dual-State Emission by Isomeric Substitution

It is attractive but highly challenging to achieve controllable regulation of photophysical properties of pure organic luminogens, due to distinct work mechanisms and molecular structures. Here, a strategy to regulate in a controllable way the emission behavior of luminogens is reported, according to which long-lived aggregation-induced emission (AIE) can be switched to short-lived dual-state emission (DSE) by an isomer-based substitution reaction. Three luminogens with sharply different photophysical behaviors, including aggregation-induced phosphorescence and dual-state fluorescence emission, were obtained through a substitution reaction with three isomers. Freely rotating structures are attributed to aggregation-induced phosphorescence behavior, whereas twisted rigidification of the molecule greatly contributes to its dual-state emission phenomenon. This work contributes to the controlled regulation of photophysical behaviors through simple reactions and provides a solid evidence to support the key role of the prohibition of intramolecular rotation in aggregation-induced emission process and molecular design of dual-state emitters.     

有机同秩物概念及单取代烷烃同秩物生成焓和电离能变化规律

提出了“有机同秩列”、“有机同秩物”、“有机同秩异构体”等概念体系,并以单取代烷烃同秩物Xi-（CH2）/-H（Xi=F、CI、Br、I、NO2、CN、NC、OH、NH2、SH、COOH、CHO）为例,对其气相标准摩尔生成焓（△rHm）、电离能（IP）的结构-性能关系进行了研究,分别对j=2～8的七组同秩物的生成焓及j=2～4的三组同秩物的电离能建立了数学模型：△rHm（j）=a＋b△iHm（1）＋cPEI（R）和IP（j）：a＋bIP（1）＋bPEI（R）,得到了有意义的结果．研究表明,从有机同秩物的角度可以建立一种新的分子结构．性能相关方法,它与有机同系物方法相互独立又互为补充．本文提出的概念体系不仅增加了新的有机化学理论和概念,还为有机物结构-性能变化规律的研究开辟了新视角．     

Triplet fusion delayed fluorescence materials for OLEDs

The development of fluorescent materials capable of harvesting triplet excitons efficiently is of great importance in achieving high-performance low-cost organic light-emitting diodes (OLEDs). Among the three mechanisms converting triplet to singlet excitons, triplet fusion delayed fluorescence (TFDF) plays a key role in the demonstration of highly efficient and reliable OLEDs, especially blue devices, for practice applications. This review focuses on the recent development of TFDF materials and their applications in OLEDs. Fundamental TFDF mechanism, molecular design principles, and the structure-property relationship of TFDF materials with a particular emphasis on their different excited state characters, are presented and discussed. Moreover, the future perspectives and ongoing challenges of TFDF materials are also highlighted.     

Remarkable mechanochromism and force-induced thermally activated delayed fluorescence enhancement from white-light-emitting organic luminogens with aggregation-induced emission

The development of organic materials with white-light emission and thermally activated delayed fluorescence (TADF) properties in the solid state remain a challenge. Herein, a series of white-light-emitting organic luminogens have been developed and are found to show aggregation-induced delayed fluorescence (AIDF) characteristics. The AIDF emitters present dual-emission consisted of prompt fluorescence and TADF in the crystalline state. Their white-light emissions can be easily tuned by altering the chemical structure and connecting position of the heterocyclic aromatic substituent. Under the stimuli of mechanical force and solvent vapor, the compounds exhibit remarkable and reversible mechanochromism, in which their emission colors are switchable between white and yellow. Upon grinding, they also display linearly tunable luminescence colors, as well as force-induced TADF enhancement, which may be associated with the more compact molecular packing and the restriction of intramolecular motions. The results from time-resolved emission scanning and theoretical calculation suggest that the dual-emission of the AIDF luminogens likely results from the twisted intramolecular charge transfer transitions of the molecules, and the reversible mechanochromism properties probably stem from the interconversion of the quasi-axial and the quasi-equatorial conformations.     

Recent Advances in Aggregation-Induced Electrochemiluminescence

The emergence of the rising alliance between aggregation-induced emission (AIE) and electrochemiluminescence (ECL) is defined as aggregation-induced electrochemiluminescence (AIECL). The booming science of AIE has proved to be not only distinguished in luminescent materials but could also inject new possibility into ECL analysis. Especially in the aqueous phase and solid state for hydrophobic materials, AIE helps ECL circumvent the dilemma between substantial emission intensity and biocompatible media. The wide range of analytes makes ECL an overwhelmingly interesting analytical technique. Therefore, AIECL has gained potential in clinical diagnostics, environmental assays, and biomarker detections. This review will focus on introduction of the novel concept of AIECL, current applied luminophores, and related applications developed in recent years.     

Supramolecular Assemblies with Aggregation-Induced Emission Properties for Sensing and Detection

The fabrication of new supramolecular materials for real-time detection of analytes including ions, organic pollutants, gases, biomolecules, and drugs is of pivotal importance in industrial manufacture, clinical treatment, and environmental remediation. Incorporating fluorescent molecules with distinct aggregation-induced emission (AIE) effects into supramolecular assemblies has received much attention over the past two decades, owing to the remarkable performance of the AIE-active supramolecular materials in sensing and detection. In this minireview, we summarize the recent progress of superior detection systems on the basis of supramolecular assemblies accompanied with AIE features. We envision that this minireview will be helpful and timely for relevant researchers to stimulate new thinking for constructing new AIE-based supramolecular materials with advanced architectures for effective sensing and detection.     

近红外发光的聚集诱导发光分子在抗菌光动力治疗中的应用

抗生素的误用和滥用,使越来越多的耐药细菌出现,对人类构成致命威胁。近年来,聚集诱导发光材料的发展和生物学科的交叉融合,为治疗细菌感染提供了许多创新思路。相对于紫外/可见光,近红外(NIR)光具有优异的组织深度渗透性和安全性等独特优势,有利于构建光动力抗菌平台进行深度治疗。随着对聚集诱导发光分子(AIEgens)设计及应用的不断探索,AIEgens在光动力抗菌治疗中表现出巨大的应用潜力。本文综述了NIR发光的AIEgens通过光动力疗法治疗细菌感染的研究进展,讨论了不同结构的聚集诱导发光材料存在的主要问题以及该领域当前的挑战和前景。     

聚集诱导发光分子的光电功能与器件应用

光电功能分子通常以薄膜和聚集体的形式显示功能, 聚集诱导发光（AIE）分子体系的发现为解决固态下聚集诱导荧光猝灭（ACQ）难题提供了新的思路. 本文总结了近年来本课题组发展的一系列AIE 分子, 侧重介绍这些AIE 分子的光电功能与器件应用, 特别是在有机电致发光器件和有机激光方面的应用. AIE 材料显示非常高的电致发光效率, 在显示与白光器件方面潜力巨大. 在发展电泵有机激光方面, AIE 材料特点突出, 是最有前景的一类材料.