2,6,8‐Trisubstituted 3‐Hydroxychromone Derivatives as Fluorophores for Live‐Cell Imaging

We present the synthesis and photophysical characterisation of a series of structurally diverse, fluorescent 2,6,8‐trisubstituted 3‐hydroxychromone derivatives with high fluorescence quantum yields and molar extinction coefficients. Two of these derivatives ( 9 and 10 a ) have been studied as fluorophores for cellular imaging in HeLa cells and show excellent permeability and promising fluorescence properties in a cellular environment. In addition, we have demonstrated by photophysical characterisation of 3‐isobutyroxychromone derivatives that esterification of the 3‐hydroxyl group results in acceptable and useful fluorescence properties.     

A Water‐Soluble ESIPT Fluorescent Probe with High Quantum Yield and Red Emission for Ratiometric Detection of Inorganic and Organic Palladium

A novel fluorescent probe with a high quantum yield (0.41), large Stokes shifts (255 nm), and red emission (635 nm) was designed to detect all typical oxidation states of palladium species (0, +2, +4) by palladium‐mediated terminal propargyl ethers cleavage reaction in water solution without any organic media. The probe showed a high selectivity and excellent sensitivity for palladium species, with a detection as low as 57 nM (6.2 μg L^?1).     

Excited state intramolecular proton transfer (ESIPT) from phenol OH (OD) to adjacent “aromatic” carbons in simple biphenyls

This work reports results of further studies on a new class of excited state intramolecular proton transfer (ESIPT), from phenol OH to adjacent aromatic carbon atoms of suitably designed biphenyl systems. For this purpose, a number of 2-phenylphenols 3–6 with methyl and methoxy substituents on the adjacent proton accepting phenyl ring were synthesized. In particular, we were also interested in studying the effect of an acetyl (ketone) substituent on the proton accepting ring (biphenyl 7) and the effect on the photochemistry when the ketone is reduced to alcohol (biphenyl 8). All compounds except for 7 were found to undergo deuterium exchange (Ф_ex = 0.019–0.079) primarily at the 2′-position on photolysis in 1:3 D₂O–CH₃CN. This is consistent with a reaction mechanism involving initial ESIPT from the phenol OH to the 2′-position of the adjacent phenyl ring, to generate a biphenyl quinone methide intermediate which rapidly tautomerizes back to starting material. Biphenyl 8 also undergoes a competing photosolvolysis reaction (overall loss of water). Both photosolvolysis and ESIPT reactions react via isomeric quinone methide intermediates and are best interpreted as arising from an excited singlet state that possesses a large degree of charge transfer character, from the phenol ring to the attached phenyl ring. The failure of 7 to react may be due to two possible reasons: (i) high intersystem crossing rate to a non-polarized triplet excited state and/or (ii) a polarized singlet state that is now much more basic at the carbonyl oxygen. The results are consistent with qualitative examination of calculated HOMOs and LUMOs (AM1).     

A Reevaluation of the Photolytic Properties of 2‐Hydroxybenzophenone‐Based UV Sunscreens: Are Chemical Sunscreens Inoffensive?

The excited states of a set of popular sunscreen agents (2‐hydroxybenzophenone, oxybenzone, and sulisobenzone) are studied by using femto‐ and nanosecond time‐resolved spectroscopy. Upon excitation, the compounds undergo an ultrafast excited‐state intramolecular proton transfer (ESIPT) reaction as the major energy‐wasting process and the rate constant of this reaction is k=2×10¹² s^?1. The ESIPT yields a keto conformer that undergoes a fast, picosecond internal conversion decay. However, a photodegradative pathway is a monophotonic H?O bond breakage that subsequently leads to trace yields of phenoxyl radicals. Because potentially harmful phenoxyl radicals are formed upon irradiation of sunscreen agents, care should be taken about their reactivity towards biologically relevant compounds.     

水杨醛衍生物激发态下的质子转移过程及在荧光探针领域的应用

从电子结构控制理论出发,通过在酚羟基对位引入吸电子取代基团稳定水杨醛中激发态的酮式构象,制备了目标化合物5-对氰基苯基-水杨醛(CN-SA).光谱测试结果显示,CN-SA表现出典型的ESIPT态荧光分子特性,而且辐射跃迁过程的酮式分配比例显著提高,荧光强度和颜色变化明显.CN-SA的荧光光谱不但能够对外围溶剂环境进行选择性识别,而且对溶解和聚集过程(聚集效应)及外围氢键形成能力的变化(pH效应和阴离子效应)等具有特异性响应,其变化可以定量表达.CN-SA仅通过结构微调即实现醇-酮构象的显著变化,可作为一个简单的多重刺激响应型荧光探针.     

激发态分子内质子转移化合物的性能及作为荧光化学传感器的应用研究

本文简述了激发态分子内质子转移(ESIPT)化合物的理论研究进展,并对其作为荧光化学传感器的应用作了简要的综述,列举了一些代表性的工作,以期对该类化合物的后续研究工作有所帮助.     

Target‐Triggered NIR Emission with a Large Stokes Shift for the Detection and Imaging of Cysteine in Living Cells

Background autofluorescence from biological systems generally reduces the sensitivity of a fluorescent probe for imaging biological targets. Addressing this challenge requires the development of fluorescent probes that produce emission in the near‐infrared region. Herein, we report the design and synthesis of a fluorescent probe that generates an NIR emission with a large Stokes shift upon the selective response to Cys over Hcy and GSH. The probe is designed to consist of two Cys‐sensing sites, an acrylate ester and an aldehyde installed ortho to each other. The reaction of the probe with Cys triggers an excited state intramolecular proton transfer process upon photo‐excitation, thereby producing an NIR emission with a large Stokes shift. Accordingly, this probe hold great promise for the selective detection of Cys in biological systems. We further demonstrate the capacity of this probe for Cys imaging in living cells.     

Proton‐Transfer Reactions of Acridine in Water‐Containing Ionic‐Liquid‐Rich Mixtures

To assess the potential of ionic liquids (ILs) as a solubilizing media that facilitates proton‐transfer reactions, acridine prototropism is investigated using UV/Vis molecular absorbance as well as steady‐state and time‐resolved fluorescence with different ILs in the presence of a small amount of dilute acid or base. It is found that protonation and deprotonation of acridine, when dissolved in different ILs, can be triggered by the addition of a small amount of dilute aqueous HCl and NaOH, respectively, in both the ground and excited states, irrespective of the identity of the IL. However, the amount of dilute acid/base needed to protonate/deprotonate acridine dissolved in different ILs is found to vary from one IL to another. Steady‐state fluorescence measurements also imply the presence of interactions between the acidic proton(s) of IL cation and excited acridine. The interconversion of neutral and protonated acridine, as well as the presence of a weakly fluorescent complex between excited acridine and the acidic proton(s) of the IL cation, is further corroborated by the parameters recovered from the fitting of the excited‐state intensity‐decay data. It is established that ILs as solubilizing media readily support facile proton transfer in both ground and excited states.     

Far‐Red and Near‐IR AIE‐Active Fluorescent Organic Nanoprobes with Enhanced Tumor‐Targeting Efficacy: Shape‐Specific Effects

The rational design of high‐performance fluorescent materials for cancer targeting in vivo is still challenging. A unique molecular design strategy is presented that involves tailoring aggregation‐induced emission (AIE)‐active organic molecules to realize preferable far‐red and NIR fluorescence, well‐controlled morphology (from rod‐like to spherical), and also tumor‐targeted bioimaging. The shape‐tailored organic quinoline–malononitrile (QM) nanoprobes are biocompatible and highly desirable for cell‐tracking applications. Impressively, the spherical shape of QM‐5 nanoaggregates exhibits excellent tumor‐targeted bioimaging performance after intravenously injection into mice, but not the rod‐like aggregates of QM‐2.     

Unusual Aggregation‐Induced Emission of a Coumarin Derivative as a Result of the Restriction of an Intramolecular Twisting Motion

Aggregation‐induced emission (AIE) is commonly observed for propeller‐like luminogens with aromatic rotors and stators. Herein, we report that a coumarin derivative containing a seven‐membered aliphatic ring (CD‐7) but no rotors showed typical AIE characteristics, whereas its analogue with a five‐membered aliphatic ring (CD‐5) exhibited an opposite aggregation‐caused quenching (ACQ) effect. Experimental and theoretical results revealed that a large aliphatic ring in CD‐7 weakens structural rigidity and promotes out‐of‐plane twisting of the molecular backbone to drastically accelerate nonradiative excited‐state decay, thus resulting in poor emission in solution. The restriction of twisting motion in aggregates blocks the nonradiative decay channels and enables CD‐7 to fluoresce strongly. The results also show that AIE is a general phenomenon and not peculiar to propeller‐like molecules. The AIE and ACQ effects can be switched readily by the modulation of molecular rigidity.     

2-(2′-羟苯基)苯并噁唑氨基衍生物电子结构和光谱性质的理论研究

采用量子化学方法优化了间位和对位2-(2′-羟苯基)苯并噁唑氨基取代衍生物(4-AHBO和5-AHBO)基态的第一单重激发态所有可能的稳定构型, 分析了这些异构体在不同溶剂中的相对稳定性. 利用含时密度泛函理论(TDDFT)的不同泛函, 计算了4-AHBO和5-AHBO各异构体在溶剂中的吸收与发射光谱, 考察了它们的电子结构和光谱特征. 结果表明, 4-AHBO(5-AHBO)的双荧光不是由同一种异构体发射的, 而是来源于不同异构体的发射: 长波区的荧光由酮式构型发射, 短波区的发射则可能由四种醇式异构体共同产生. 另外, 也解释了5-AHBO在质子溶剂中光谱异常的原因, 分析了不同氨基取代位和溶剂极性的变化对各异构体构型、光谱性质及电子结构的影响. 理论预测的光谱与实验结果一致.     

A study on multifunctional protein fibre with UV protection,moth repellency and antibacterial properties using ESIPT core containing benzimidazole and benzothiazole based functional acid azo dyes

Water soluble fluorescent acid azo dyes with benzimidazole and benzothiazole component having excited state intramolecular proton transfer (ESIPT) core were synthesised by diazo coupling. The structure of the dyes were analysed and confirmed by Fourier Transform Infrared – spectroscopy (FT-IR), elemental analysis, ¹H NMR and ¹³C NMR analysis. Absorption and emission characteristics of the dyes were studied in different polarity solvents shown bathochromic (red) shift as solvent polarity increases. Wool and silk fabric dyed with synthesised dyes displayed high exhaustion, uniform dyeing and good wet fastness properties. The dyed substrate showed green and purple fluorescence under UV light (366 ​nm) along with UV protection. Dyed wool fabric was also assessed for antibacterial activity by calculation of bacterial reduction Staphylococcus Auerus (Gram positive), Klebsiella Pneumonia (Gram negative) bacteria. The dyed wool were also examined for the resistivity against insect pests Anthrenus Flavipies (Le Conte) by calculation of the fabric weight loss, Mortality of moth and visible assessment of fabric attacked by moth after 14 days in given conditions. Consequently, it was demonstrated that wool fabric dyed with Benzimidazole and benzothiazole based acid dyes had various functionalities, such as UV protection, antibacterial activity and mild moth repellency.     

A water‐soluble,AIE‐active polyelectrolyte for conventional and fluorescence lifetime imaging of mouse neuroblastoma neuro‐2A cells

A new conjugated polyelectrolyte containing tetraphenylethene units in the backbone is synthesized and characterized. This polyelectrolyte is water‐soluble and exhibits aggregation‐induced emission (AIE) behavior. It is biocompatible and can be directly used in conventional and fluorescence lifetime imaging of mouse neuroblastoma neuro‐2A cells, providing useful information of cellular morphology and intracellular aggregation or motion. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 672–680     

Aromatic oxadiazole‐based conjugated polymers with excited‐state intramolecular proton transfer: Their synthesis and sensing ability for explosive nitroaromatic compounds

Aromatic polyoxadiazole derivatives containing 9,9′‐dioctylfluorene were successfully synthesized via the Suzuki coupling reaction. The oxadiazole moiety in the polymer backbone was linked with the bis(hydroxyphenyl) group in its 2‐position to exhibit a large Stokes shift in the emission spectrum due to the excited‐state intramolecular proton transfer. To prepare the polymer via the Suzuki cross‐coupling reaction, the hydroxyl group in the monomer was protected with the t‐butoxycarbonyl group before polymerization and removed after polymerization to a desirable extent. The polymer with the free hydroxyl group showed a considerable sensitivity for nitroaromatic compounds, exhibiting fluorescence quenching in a chloroform solution. The interaction between the electron‐donating OH group and electron‐deficient nitroaromatic compounds seemed to play a decisive role in fluorescence quenching. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2059–2068, 2006     

A CASSCF/CASPT2 insight into excited‐state intramolecular proton transfer of four imidazole derivatives

Excited‐state intramolecular proton transfer (ESIPT) of four imidazole derivatives, 2‐(2′‐hydroxyphenyl)imidazole (HPI), 2‐(2′‐hydroxyphenyl)benzimidazole (HPBI), 2‐(2′‐hydroxyphenyl)‐1H‐phenanthro[9,10‐d]imidazole (HPPI) and 2‐(2′‐hydroxyphenyl)‐1‐phenyl‐1H‐phenanthro[9,10‐d]imidazole (HPPPI), were studied by the sophisticated CASSCF/CASPT2 methodology. The state‐averaged SA‐CASSCF method was used to optimize their geometry structures of S₀ and S₁ electronic states, and the CASPT2 calculations were used for the calibration of all the single‐point energies, including the absorption and emission spectra. A reasonable agreement is found between the theoretical predictions and the available experimental spectral data. The forward ESIPT barriers of four target compounds gradually decrease with the increase of molecular size. On the basis of the present calculations, it is a plausible speculation that the larger the size, the faster is the ESIPT rate, and eventually, HPPPI molecule can undergo a completely barrierless ESIPT to the more stable S₁ keto form. Additionally, taking HPI as a representative example, the radiationless decays connecting the S₀ and S₁/S₀ conical intersection structures were also studied by constructing a linearly interpolated internal coordinate (LIIC) reaction path. The qualitative analysis shows that the LIIC barrier of HPI in the keto form is remarkably lower than that of its enol‐form, indicating that the former has a big advantage over the latter in the nonradiative process. © 2015 Wiley Periodicals, Inc.     

Self‐Assembly and Aggregate‐Induced Enhanced Emission of Amphiphilic Fluorescence Dyes in Water and in the Solid State

1‐Cyano‐1,2‐bis(biphenyl)ethene (CNBE) derivatives with a hexa(ethylene glycol) group as an amphiphilic side chain were synthesized and the self‐assembling character and fluorescence behavior were investigated. The amphiphilic derivatives showed aggregate‐induced enhanced emission (AIEE) in water and in the solid state. The fluorescence quantum yield increased as the rigidity of the aggregates increased (i.e., in ethyl acetate<in water<in the solid state). As determined from measurements of fluorescence spectra, fluorescence quantum yields, and fluorescence lifetimes, a key factor for the enhanced emission is suppression of the nonradiative decay process arising from restricted molecular motion. Additionally, the difference in the emission rate constant is not negligible and can be used to interpret the difference in fluorescence quantum yield in water and in the solid state.     

Decomposition‐Assembly of Tetraphenylethylene Nanoparticles With Uniform Size and Aggregation‐Induced Emission property

Tetraphenylethylene (TPE)‐substituted poly(allylamine hydrochloride) (PAH‐g‐TPE) is synthesized by a Schiff base reaction between PAH and TPE‐CHO. The PAH‐g‐TPE forms micelles in water at pH 6, which are further transformed into pure TPE‐CHO nanoparticles (NPs) with a diameter of ≈300 nm after incubation in a solution of low pH value. In contrast, only amorphous precipitates are obtained when TPE‐CHO methanol solution is incubated in water. The aggregation‐induced emission feature of the TPE molecule is completely retained in the TPE NPs, which can be internalized into cells and show blue fluorescence. Formation mechanism of the TPE NPs is proposed by taking into account the guidance effect of linear and charged PAH molecules, and the propeller‐stacking manner between the TPE‐CHO molecules.