Synthesis and Characterization of Diketopyrrolopyrrole-Based Aggregation-Induced Emission Nanoparticles for Bioimaging

Conventional fluorescent dyes have the property of decreasing fluorescence due to aggregation-caused quenching effects at high concentrations, whereas aggregation-induced emission dyes have the property of increasing fluorescence as they aggregate with each other. In this study, diketopyrrolopyrrole-based long-wavelength aggregation-induced emission dyes were used to prepare biocompatible nanoparticles suitable for bioimaging. Aggregation-induced emission nanoparticles with the best morphology and photoluminescence intensity were obtained through a fast, simple preparation method using an ultrasonicator. The optimally prepared nanoparticles from 3,6-bis(4-((E)-4-(bis(40-(1,2,2-triphenylvinyl)-[1,10-biphenyl]-4-yl)amino)styryl)phenyl)-2,5-dihexyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DP-R2) with two functional groups having aggregation-induced emission properties and additional donating groups at the end of the triphenylamine groups were considered to have the greatest potential as a fluorescent probe for bioimaging. Furthermore, it was found that the tendency for aggregation-induced emission, which was apparent for the dye itself, became much more marked after the dyes were incorporated within nanoparticles. While the photoluminescence intensities of the dyes were observed to decrease rapidly over time, the prepared nanoparticles encapsulated within the biocompatible polymers maintained their initial optical properties very well. Lastly, when the cell viability test was conducted, excellent biocompatibility was demonstrated for each of the prepared nanoparticles.     

Direct Observation of Aggregation-Induced Emission Mechanism

The mechanism of aggregation-induced emission, which overcomes the common aggregation-caused quenching problem in organic optoelectronics, is revealed by monitoring the real time structural evolution and dynamics of electronic excited state with frequency and polarization resolved ultrafast UV/IR spectroscopy and theoretical calculations. The formation of Woodward–Hoffmann cyclic intermediates upon ultraviolet excitation is observed in dilute solutions of tetraphenylethylene and its derivatives but not in their respective solid. The ultrafast cyclization provides an efficient nonradiative relaxation pathway through crossing a conical intersection. Without such a reaction mechanism, the electronic excitation is preserved in the molecular solids and the molecule fluoresces efficiently, aided by the very slow intermolecular charge and energy transfers due to the well separated molecular packing arrangement. The mechanisms can be general for tuning the properties of chromophores in different phases for various important applications.     

Covalent Attachment of Aggregation-Induced Emission Molecules to the Surface of Ultrasmall Gold Nanoparticles to Enhance Cell Penetration

Three different alkyne-terminated aggregation-induced emission molecules based on a para-substituted di-thioether were attached to the surface of ultrasmall gold nanoparticles (2 nm) by copper-catalyzed azide–alkyne cycloaddition (click chemistry). They showed a strong fluorescence and were well water-dispersible, in contrast to the dissolved AIE molecules. The AIE-loaded nanoparticles were not cytotoxic and easily penetrated the membrane of HeLa cells, paving the way for an intracellular application of AIE molecules, e.g., for imaging.     

Multistimuli-Responsive Luminescence of Naphthalazine Based on Aggregation-Induced Emission

Stimuli-responsive luminescent materials, which are dependent on changes in physical molecular packing modes, have attracted more and more interest over the past ten years. In this study, 2,2-dihydroxy-1,1-naphthalazine was synthesized and shown to exhibit different fluorescence emission in solution and solid states with characteristic aggregation-induced emission (AIE) properties. A remarkable change in the fluorescence of 2,2-dihydroxy-1,1-naphthalazine occurred upon mechanical grinding, heating, or exposure to solvents. According to the characterization by solid-state fluorescence spectroscopy, X-ray crystallography, differential scanning calorimetry, and X-ray powder diffraction, the fluorescence change could be attributed to transitions between two structurally different polymorphs. These significant properties could also give 2,2-dihydroxy-1,1-naphthalazine more potential applications as a multifunctional material.     

Aggregation-Induced Emission of Triphenyl-Substituted Tristyrylbenzenes

The synthesis, properties and X-ray single-crystal structures of two regioisomeric triphenyl tristyrylbenzenes are reported. Both C_3v and C_s derivatives display aggregation-induced emission (AIE) behavior. Regioisomerism impacts the solid-state intermolecular interactions, the photophysical characteristics and photostability in solution.     

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.     

Aggregation-Induced Emission: Recent Advances in Materials and Biomedical Applications

The concept of aggregation-induced emission (AIE) has opened new opportunities in many research fields. Motivated by the unique feature of AIE fluorogens (AIEgens), during the past decade, many AIE molecular probes and AIE nanoparticle (NP) probes have been developed for sensing, imaging and theranostic applications with excellent performance outperforming conventional fluorescent probes. This Review summarizes the latest advancement of AIE molecular probes and AIE NP probes and their emerging biomedical applications. Special focus is to reveal how the AIE probes are evolved with the development of new multifunctional AIEgens, and how new strategies have been developed to overcome the limitations of traditional AIE probes for more translational applications via fluorescence imaging, photoacoustic imaging and image-guided photodynamic/photothermal therapy. The outlook discusses the challenges and future opportunities for AIEgens to advance the biomedical field.     

Quantitative Prediction of Aggregation-Induced Emission: A Full Quantum Mechanical Approach to the Optical Spectra

Full quantum mechanical (FQM) calculation of the excited state of aggregation-induced-emission (AIE) materials is highly sought but still a challenging task. Herein, we employed the recently developed electrostatically embedded generalized molecular fractionation (EE-GMF) method, a method based on the systematic fragmentation approach, to predict, for the first time, the spectra of a prototype AIE fluorophore: di(p-methoxylphenyl)dibenzofulvene (FTPE). Compared to the single molecular or QM/MM calculations, the EE-GMF method shows significantly improved accuracy, nearly reproducing the experimental optical spectra of FTPE in both condensed phases. Importantly, we show that the conventional restriction of the intramolecular rotation mechanism cannot fully account for AIE, whereas the two-body intermolecular quantum mechanical interaction plays a crucial role in AIE.     

具有聚集诱导发光特性的四苯基乙烯研究进展

具有聚集诱导发光(aggregation-induced emission,AIE)性质的四苯基乙烯及其衍生物(tetraphenylethenes,TPEs)因其发光性能优良、合成简便、易多功能化而越来越受到关注.本文着重对最近几年TPEs的AIE性质研究进展进行综述.在阐述结构与AIE性质之间关系的同时,介绍了TPEs在生物、化学传感器及其它方面的应用, 并对TPEs的设计与应用给予展望.     

Photophysics of 9,9-Dimethylacridan-Substituted Phenylstyrylpyrimidines Exhibiting Long-Lived Intramolecular Charge-Transfer Fluorescence and Aggregation-Induced Emission Characteristics

Six pyrimidine-based push–pull systems substituted at positions C2 and C4/6 with phenylacridan and styryl moieties, employing methoxy or N,N-diphenylamino donors, have been designed and synthesized through cross-coupling and Knoevenagel reactions. X-ray analysis confirmed that the molecular structure featured the acridan moiety arranged perpendicularly to the residual π system. Photophysical studies revealed significant differences between the methoxy and N,N-diphenylamino chromophores. Solvatochromic studies revealed that the methoxy derivatives showed dual emission in polar solvents. Time-resolved spectroscopy revealed that the higher energy band involved very fast (<80 ps) fluorescence, whereas the lower energy one included long components (≈30 ns) due to long-lived intramolecular charge-transfer fluorescence. In contrast to N,N-diphenylamino chromophores, the methoxy derivatives also showed aggregation-induced emission in mixtures of THF/water, as well as dual emission in thin films, covering almost the whole visible spectrum with corresponding chromaticity coordinates not far from that of pure white light. These properties render the methoxy derivatives as very promising organic materials for white organic light-emitting diodes.     

高性能聚集诱导发光纳米探针用于肿瘤切除手术导航

远红/近红外(FR/NIR)发射荧光材料因其在生物成像领域的巨大应用潜力而受到广泛关注.然而,根据"能隙"规则,电子带隙减小时,非辐射失活途径占据能量耗散主导地位,因此制备高量子产率、长发射波长的有机FR/NIR材料仍然是一个挑战.本文通过引入扭曲构象基团(四苯基乙烯)对分子聚集态进行调控,合成了一系列基于苯并硒二唑的...     

含不同烷基链四苯基丁二烯衍生物的聚集诱导发光及力致变色性能

设计合成了带有不同长度烷基链、不同极性取代基的四苯基丁二烯(TPB)衍生物TPB-COOCH₃-1~6和TPB-COOH-1~6, 目标化合物均具有显著的聚集诱导发光(AIE)特性及较高的固态荧光量子效率. 烷基链长及取代基极性都会影响目标化合物在聚集时分子排列及分子运动的受限程度, 从而调控其AIE行为. 带有羧酸甲酯的TPB-COOCH₃-1~6中, 丙基取代的TPB-COOCH₃-3在四氢呋喃/水(THF/H₂O)体系中荧光发射增强最为显著; 而羧基取代的TPB-COOH-1~6中, 因亲水性增加, 己基取代的TPB-COOH-6荧光强度增加的倍数最大; 并且, TPB-COOH系列化合物荧光增强的倍数明显低于相同烷基取代的甲酯衍生物TPB-COOCH₃. 此外, 牛血清白蛋白、人血清白蛋白和带有羧基的AIE化合物掺杂时明显影响其固态时的发光及其力致变色性质, 尤其是研磨后会明显提高其荧光强度.     

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。     

Tricyano-Methylene-Pyridine Based High-Performance Aggregation-Induced Emission Photosensitizer for Imaging and Photodynamic Therapy

Photosensitizers equipped with high reactive oxygen species (ROS) generation capability and bright emission are essential for accurate tumor imaging and precise photodynamic therapy (PDT). However, traditional aggregation-caused quenching (ACQ) photosensitizers cannot simultaneously produce desirable ROS and bright fluorescence, resulting in poor image-guided therapy effect. Herein, we report an aggregation-induced emission (AIE) photosensitizer TCM-Ph with a strong donor–π–acceptor (D–π–A) structure, which greatly separates the HOMO–LUMO distribution and reduces the ΔE_ST, thereby increasing the number of triplet excitons and producing more ROS. The AIE photosensitizer TCM-Ph has bright near-infrared emission, as well as a higher ROS generation capacity than the commercial photosensitizers Bengal Rose (RB) and Chlorine e6 (Ce6), and can effectively eliminate cancer cells under image guidance. Therefore, the AIE photosensitizer TCM-Ph has great potential to replace the commercial photosensitizers.     

Tunable Aggregation-Induced Emission of Imidazole Hydrazones by pH and Anions

Aggregation-induced emission (AIE) materials have drawn great attention for applications as organic light-emitting diodes (OLED) and probes. The applications are, however, restricted by the complex syntheses and hydrophobic properties. Herein, a one-step synthesis of an AIE material based on imidazole hydrazone is assessed. Protonation of the imidazole-H leads to emission color change from yellow to green in the solid state. The emission color is recovered upon imidazole-H⁺ deprotonation. Moreover, the emission wavelength shifts from 532 to 572 nm by anion exchange. In addition, an enhanced emission (Φ_F up to 22.6 %) was obtained with the Br⁻ anion compared with NTf₂⁻, SbCl₅⁻, PF₆⁻, and OTf⁻ anions. X-ray crystallography studies together with theoretical calculations show that the enhanced emission of hydrazone salts arises from strong hydrogen bonding between the hydrazone proton and the halide ion (Cl⁻ or Br⁻).     

Synthesis and Characterization of Liquid-Crystalline Tetraoxapentacene Derivatives Exhibiting Aggregation-Induced Emission

A series of new tetrakis(dialkoxyphenyl) dicyanotetraoxapentacene derivatives ( 1 a – c ) were prepared by reaction of the appropriate terphenyl diols with tetrafluoroterephthalonitrile in good yields. Compounds 1 b and 1 c , which bear hexyloxy and decyloxy side chains, exhibited columnar hexagonal mesophases, as shown by polarized optical microscopy, variable-temperature powder X-ray diffraction, and differential scanning calorimetry. Single-crystal X-ray diffraction of methoxy-substituted 1 a revealed that the dicyanotetraoxapentacene core is highly planar, consistent with the notion that these molecules are able to stack in columnar mesophases. A detailed photophysical characterization showed that these compounds exhibit aggregation-induced emission in solution, emission in nonpolar solvents, weak emission in polar solvents, and strong emission in the solid state both as powder and in thin films. These observations are consistent with a weakly emissive charge-transfer state in polar solvents and a more highly emissive locally excited state in nonpolar solvents.     

Measurement of Solubilization Location in Micelles Using Anchored Aggregation-Induced Emission Donors

Solubilization locations play a critical role in developing advanced surfactants and improving solubilization power in micelle-based applications. However, the current polarity-based techniques for measuring solubilization locations could come to conflicting conclusions. The key challenge is the unpredictable polarities in the micellar microenvironment. Now, an approach that is independent of micellar polarities is used to measure solubilization locations by covalently linking tetraphenylethylene (TPE) to the alkyl chain end of cationic surfactants. The solubilization locations of solubilized acceptors in the TPE-cored spherical micelles were accurately measured by calculating the Förster resonance energy transfer distance between anchored TPE donors and solubilized acceptors. Solubilization locations of solubilized substances in the micellar interior and at the micellar surface depend on their size and hydrophobicity, respectively.     

具有聚集诱导发光效应的聚炔材料的合成及光学性能研究

合成了三种含有四苯基乙烯结构的双炔烃.这些双炔烃单体通过在CuCl催化下在邻二氯苯中进行的均聚反应可以高产率地生成线型聚炔.所得聚合物均可很好地溶解于常见有机溶剂中,并具有很高的热稳定性.这类聚炔材料在溶液态时几乎不发光,但在聚集态或者固态下可高度发光,表现出典型的聚集诱导发光性质.同时,这些聚合物具有高透光性,可以允许整个可见光区的光透过.其薄膜在400～1700 nm宽波长范围内表现出高折射率（n=1.7787～1.6543）和低色差（D'=0.0003）.紫外光照射可诱使聚合物薄膜发生交联过程,从而调控其折射率数值,并可生成高分辨率的荧光图案.     

含磷酰杂菲苯甲酸对苯二酯的聚集诱导发光增强性能及其在检测过渡金属离子中的应用

有机化合物因成膜以后荧光淬灭而使其应用受到很大限制, 所以研究、开发能在聚集状态下呈现优异发光性能的新材料就尤为重要. 由于分子间π-π和极性共同相互作用, 使得磷酰杂菲环的转动受到限制, 从而使苯甲酸-2-[6-氧化-6-氢-二苯基(c,e)＜1,2＞氧杂磷酰基]-1,4-二羟基苯二酯(OP)在达到一定规整聚集程度时, 荧光强度成倍增加, 具有了聚集诱导发光增强(AIEE)性质. 实验结果表明: 浓度低于1×10^－6 mol•L^－1 的OP会失去AIEE性质; 浓度为1×10^－4 mol•L^－1的Hg^2＋, Fe^2＋和 Fe^3＋会分别淬灭浓度为1×10^－5 mol•L^－1 OP荧光强度的26%, 34%, 74%, 而Pb^2＋, Zn^2＋, Cd^2＋, Co^2＋, Mn^2＋, Cu^2＋, Ni^2＋, Ag^＋等离子的淬灭效率却很低, 这一性质表明该化合物可以用作过渡金属离子的特异性检测材料.