A Mechanochromic Single Crystal: Turning Two Color Changes into a Tricolored Switch

The single crystal of M‐4‐B was obtained by attaching the boron of BH₃ to the amine linker between a tetraphenylethylene (TPE) unit and rhodamine B. M‐4‐B showed a novel sequential tricolor switching from dark blue to bluish‐green and to a reddish color upon grinding. The boron atom played a key role in developing the single crystal.     

Mechanically Induced Multicolor Change of Luminescent Materials

Mechanofluorochromic or piezochromic fluorescence chemistry involves the switching and tuning of the luminescent properties of solid‐state materials induced by exogenous forces, such as grinding, shearing, compression, tension, and so forth. Up until now, most reported mechanochromic systems, including liquid crystals, organic molecules, organometallic compounds, polymers, and dye‐doped polymers, have displayed reversible two‐color changes, which arise from either supramolecular or chemical structure transformations. However, fluorescent materials that undergo mechanically induced multicolor changes remain rare; this Minireview is focused on such materials. Topics are categorized according to the different applied forces that are required to induce the multicolor change, including mechanical control of either the supramolecular structures or the chemical structures, and mechanical control of both the supramolecular structures and chemical structures.     

The Application of CdSe Quantum Dots with Multicolor Emission as Fluorescent Probes for Cell Labeling

Herein, highly luminescent CdSe quantum dots (QDs) with emissions from the blue to the red region of visible light were synthesized by using a simple method. The emission range of the CdSe QDs could be tuned from λ=503 to 606 nm by controlling the size of the CdSe QDs. Two amino acids, L ‐tryptophan (L ‐Trp) and L ‐arginine (L ‐Arg), were used as coating agents. The quantum yield (QY) of CdSe QDs (green color) with an optimized thickness could reach up to 52 %. The structures and compositions of QDs were examined by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Optical properties were studied by using UV/Vis and photoluminescence (PL) spectroscopy and a comparison was made between uncoated and coated CdSe QDs. The amino acid‐modified β‐cyclodextrin (CD)‐coated CdSe QDs presented lower cytotoxicity to cells for 48 h. Furthermore, amino acid‐modified β‐CD‐coated green CdSe QDs in HepG2 cells were assessed by using confocal laser scanning fluorescence microscopy. The results showed that amino acid‐modified β‐CD‐coated green CdSe QDs could enter tumor cells efficiently and indicated that biomolecule‐coated QDs could be used as a potential fluorescent probe.     

基于荧光染料和氧化石墨烯同步荧光法同时检测多种流感病毒亚型

分别采用三种不同发射波长的荧光染料,通过共价偶联的方式分别标记三种流感病毒亚型H1N1、H5N1和H9N2的抗体,再利用氧化石墨烯猝灭所标记染料的荧光。当将荧光标记抗体和氧化石墨烯一并加入到流感病毒溶液中时,由于抗原和抗体之间的特异性相互作用,病毒会和抗体作用而使得氧化石墨烯远离荧光染料,染料的荧光得以恢复。通过恢复的荧光发射波长位置和荧光强度,可以定性和定量检测三种不同的流感病毒亚型。在最佳实验条件下,对三种流感病毒亚型H1N1、H5N1和H9N2进行同时检测,H1N1的检出限为0.48ng/mL,线性范围为1~18ng/mL;H5N1的检出限为0.46ng/mL,线性范围为1~18.5ng/mL;H9N2的检出限为0.42ng/mL,线性范围为1~16ng/mL。该方法具有较好的稳定性、重现性和灵敏度,可实现多个流感病毒亚型的分型和同时检测。     

Manipulation of Molecular Aggregation States to Realize Polymorphism,AIE, MCL,and TADF in a Single Molecule

Multifunctional emitting materials are scarce and need to be further explored. Now, a newly anthraquinone derivative, 2‐(phenothiazine‐10‐yl)‐anthraquinone (PTZ‐AQ) was designed and synthesized and found to demonstrate polymorphism, multi‐color emission, aggregation‐induced emission (AIE), mechanochromic luminescence (MCL), and thermally activated delayed fluorescence (TADF) in its different solid forms. It is shown for the first time that TADF properties of a compound can be systematically tuned via its aggregation state. The optimized PTZ‐AQ crystal shows a small singlet–triplet energy splitting of 0.01 eV and exhibits red TADF with a photoluminescence quantum yield as high as 0.848. This study shows that the unique multiple functions can be integrated into one single compound through controlling the aggregation states, which provides a new strategy for the investigation and application of multifunctional organic materials.     

Naphthalenediimides with High Fluorescence Quantum Yield: Bright-Red,Stable, and Responsive Fluorescent Dyes

The naphthalenediimide (NDI) scaffold in contrast to its higher congeners possess low-fluorescence. In spite of elegant synthetic developments, a highly emissive NDI is quite rare to find, as well as, a green-light-emitting NDI is yet to be explored. Herein, we report a novel class of symmetric and asymmetric NH₂-substituted core-NDIs ( 1 – 5 ) with tunable fluorescence in the visible region and extending to the NIR frontier. Importantly, the bis-NH₂-substituted NDI 2 revealed quantum yield, of ≈81 and ≈68 % in toluene and DMSO, respectively, suggesting versatility of the fluorophore in a wide range of solvent polarity. The dye 1 is shown to be the first NDI-based green-light emitter. The donor piperidine group in 5 diminish the by 40-fold providing a lever to modulate the excited-state intramolecular proton transfer (ESIPT) process. Our synthetic protocol applies a Pd catalyst and a benign hydride source simplifying the non-trivial −NH₂ group integration at the NDI-core. TD-DFT calculations predicted strong intramolecular hydrogen bonds in the excited state in the bulk nonpolar medium and responsiveness to solvent polarity. The maximization of the NDI emission outlined here would further boost the burgeoning repertoire of applications of the NDI scaffold.     

Mechanochromic Behavior of Aryl‐Substituted Buta‐1,3‐Diene Derivatives with Aggregation Enhanced Emission

Three tetra‐aryl substituted 1,3‐butadiene derivatives with aggregation enhanced emission (AEE) and mechanochromic fluorescence behavior have been rationally designed and synthesized. The results suggest an effective design strategy for developing diverse materials with aggregation induced emission (AIE) and significant mechanochromic performance by employing D ‐π‐A structures with large dipole moments.     

Multicolor super-resolution fluorescence imaging via multi-parameter fluorophore detection

Understanding the complexity of the cellular environment will benefit from the ability to unambiguously resolve multiple cellular components, simultaneously and with nanometer-scale spatial resolution. Multicolor super-resolution fluorescence microscopy techniques have been developed to achieve this goal, yet challenges remain in terms of the number of targets that can be simultaneously imaged and the crosstalk between color channels. Herein, we demonstrate multicolor stochastic optical reconstruction microscopy (STORM) based on a multi-parameter detection strategy, which uses both the fluorescence activation wavelength and the emission color to discriminate between photo-activatable fluorescent probes. First, we obtained two-color super-resolution images using the near-infrared cyanine dye Alexa 750 in conjunction with a red cyanine dye Alexa 647, and quantified color crosstalk levels and image registration accuracy. Combinatorial pairing of these two switchable dyes with fluorophores which enhance photo-activation enabled multi-parameter detection of six different probes. Using this approach, we obtained six-color super-resolution fluorescence images of a model sample. The combination of multiple fluorescence detection parameters for improved fluorophore discrimination promises to substantially enhance our ability to visualize multiple cellular targets with sub-diffraction-limit resolution.     

From S,N‐Heteroacene to Large Discotic Polycyclic Aromatic Hydrocarbons (PAHs): Liquid Crystal versus Plastic Crystalline Materials with Tunable Mechanochromic Fluorescence

A novel type of discotic polycyclic aromatic hydrocarbon (PAH) based on an enlarged dibenzo[a,c]phenazine core has been developed. The large conjugated mesogenic core with increased dipole moment derived from S,N heteroatoms facilitates the formation of highly ordered columnar superstructures both in solution and bulk. Columnar mesophases, including liquid crystal (LC) and plastic crystal (PC) assemblies could form unprecedentedly based on the same PAH core. The cores are delicately modulated by the peripherical alkoxy chains. Both mesogens have mechanochromic fluorescent (MCF) character, which is also structure dependent and correlated with the different mesophase formation. For the first time, MCF properties can be realized in such a large conjugated mesogenic system.     

Protein‐Specific,Multicolor and 3D STED Imaging in Cells with DNA‐Labeled Antibodies

Photobleaching is a major challenge in fluorescence microscopy, in particular if high excitation light intensities are used. Signal‐to‐noise and spatial resolution may be compromised, which limits the amount of information that can be extracted from an image. Photobleaching can be bypassed by using exchangeable labels, which transiently bind to and dissociate from a target, thereby replenishing the destroyed labels with intact ones from a reservoir. Here, we demonstrate confocal and STED microscopy with short, fluorophore‐labeled oligonucleotides that transiently bind to complementary oligonucleotides attached to protein‐specific antibodies. The constant exchange of fluorophore labels in DNA‐based STED imaging bypasses photobleaching that occurs with covalent labels. We show that this concept is suitable for targeted, two‐color STED imaging of whole cells.     

Single-Benzene-Based Solvatochromic Chromophores: Color-Tunable and Bright Fluorescence in the Solid and Solution States

The search for structurally simple chromophores with superior fluorescence brightness and a wide range of solvent compatibility is highly desirable. Herein, a new type of single-benzene-based solvatochromic chromophore with a symmetric bifunctional structure, in which azetidine and ethoxycarbonyl moieties serve as the electron-donating and -withdrawing groups, respectively, is reported. This chromophore exhibits an extraordinary wide range of solvent compatibility and preserves excellent fluorescence quantum yields from nonpolar n-hexane to polar methanol and even in water. Unusually, the symmetric structure of the chromophore shows a distinct color change from bright green to red with increasing solvent polarity and possesses large Stokes shifts (λ=132–207 nm) in the tested solvents. Moreover, this single-benzene-based chromophore displays good photochemical stability in both solution and solid states, and even exhibits reversible mechanochromic luminescence.     

Control of Multicolor and White Emission by Adjusting the Equilibrium between Fluorophores,Lewis Acids,and Their Complexes in Polymers

Multicolor emissive materials consisting of a single luminophore, a Lewis acid, and their complex were developed. The emission colors can be tuned by changing the concentration of the solution and the ratio of mixed solvents. Various emission colors in the solid state were observed when the complexes were added to polymers in different amounts. The color change is due to equilibrium disruption between the single luminophore, the Lewis acid, and the complex thereof. White emission was observed by appropriately controlling the equilibrium by changing the amount of the complex in the polymer.     

Syntheses of Some Organic Fluorescent Dyes for Security Tickers

Five organic fluorescence dyes were synthesized by two- or three-step reactions. These synthetic meth-ods have an advantage of the simple processes, low costs and high yields. The compositions of the five compounds are characterized by IR, ^1H NMR, elemental analyses and fluorescence spectroscopies. The quantum yields of fluorescence were measured.     

Structure–Property Investigations of Substituted Triarylamines and Their Applications as Fluorescent pH Sensors

Fourteen triphenylamine derivatives functionalized with fluorophenyl, methoxyphenyl, and pyridinyl groups as respective donors and acceptors were synthesized and characterized. Their photophysical properties were systematically investigated in various solvents with different polarities. The solvent‐dependent Stokes shifts of these compounds were observed and analyzed by the Lippert–Mataga equation. The synthesized compounds, especially tris(4‐(pyridin‐4‐yl)phenyl) amine, presented pH‐dependent absorptions and emissions, indicating that these compounds might be used as pH sensors.     

Fluorescence Properties of Thiacarbocyanine Dyes at Low Temperatures

Measurements were carried out for time-resolved fluorescence spectra of dye solutions containing thiacarbocyanine and its derivatives with ethylene and vinylene bridges in the polymethine chain. At low temperature, an additional band appears in the spectrum related to an intramolecular electronic transition. Analysis of the transition lifetimes and a quantum-chemical model indicated that this transition should be attributed to a short-lived asymmetrical component formed along with the symmetrical component upon relaxation of the excited state but not appearing at room temperature due to conformational transformations.     

阴阳离子菁染料超快荧光动力学特性研究

采用飞秒荧光上转换技术,研究了阴阳离子菁染料及对应的阴离子和阳离子菁染料吸附在立方型和T型溴碘化银表面上形成J-聚集体的荧光衰减时间分辨特性,分析了几种菁染料增感体系的超快电子转移动力学过程及其对增感效率的影响.通过比较几种菁染料增感体系的荧光衰减特性,两种阴阳离子染料要明显快于阴离子染料、阳离子染料及二者的加合,说明阴阳离子染料聚集体到溴碘化银的电子注入速率较快,增感效果更好.对两种阴阳离子染料聚集体荧光衰减特性的比较,可以看出染料在T型颗粒溴碘化银上形成聚集体的荧光寿命更短,因而对T型颗粒的增感效果更好.染料Dye2的荧光衰减要快于染料Dye1,说明染料Dye2到溴碘化银的电子注入速率更快,增感效率更高.     

荧光染料探针与脱氧核糖核酸作用机理研究

核酸与各类物质的相互作用与探测核酸的结构与功能密切相关,是揭示核酸的生物功能和一些药物的作用机制的重要途径。本文研究了染料ZR、甲酚红、苏木色精等DNA的作用,给出它们在不同结合数下的生成常数。此外,还求取了它们的能量转移效率,给体－受体之间的距离。