Synthesis and properties of dendrimers possessing the same fluorophore(s) located either peripherally or off-center

Two series of phosphorus dendrimers functionalized by maleimide derivatives are synthesized, as well as three new monomeric maleimide derivatives, of which two are characterized by X-ray diffraction. The first series of phosphorus dendrimers possesses maleimide derivatives as end groups (6-48, from generation 0 to generation 3). The second series of dendrimers possesses a single copy of the same maleimide derivative linked "off-center" to a cyclotriphosphazene core, leading to dissymmetrical dendrimers; this series is synthesized from generation 0 to generation 2. The fluorescence properties of both series of dendrimers and of monomers are studied, affording new information. First, the presence of labile hydrogen extinguishes the fluorescence. Second, the grafting of the fluorophore(s) directly to the core affords highly fluorescent compounds. Finally, an original influence of the branches possessing phosphorhydrazone linkages toward the fluorescence properties is shown.     

2,2'-二苯并噁唑衍生物的合成和光性能研究

合成了16种2,2-二苯并(口恶)唑衍生物,测定了化合物的熔点、红外光谱、紫外吸收光谱、荧光发射光谱以及荧光量子产率,与1,4-二(苯并(口恶)唑1′,3′-基-2′)苯和1,4-二(苯并(口恶)唑-1′,3′-基-2′)乙烯衍生物进行了比较,讨论了它们之间光谱特性的差异.     

Fluorescence Properties of Diphenylthiazolo[4,5‐b]pyrazines Tuned by Donor‐Acceptor Substituent Effects

Fluorescence properties of 2,6‐ and 2,5‐diphenylthiazolo[4,5‐b]pyrazine (TPy) derivatives having an electron‐donating substituent (methoxy and dimethylamino) on the 6‐ and 5‐phenyl groups were studied. It was found that 2,6‐diphenyl derivatives fluoresce more efficiently than 2,5‐diphenyl derivatives. Furthermore, a 2,6‐diphenyl derivative having an additional cyano group on the 2‐phenyl ring was an excellent fluorophore showing a wide solvatochromism with great fluorescence yields. Based on the obtained spectroscopic data and mechanistic explanations concerning the substituent effects on the fluorescence properties, useful information on designing new TPy fluorophores is provided.     

一些新的芘衍生物的合成及光物理研究

本文合成了一系列新的芘衍生物，用紫外光谱和稳态荧光光谱方法研究了它们的光物理性质。结果表明，取代烷基几乎不影响芘的吸收光谱，而使芘的荧光光谱振动精细结构消失或部分消失；取代甲酰基的芘衍生物的荧光发射强烈依赖于溶剂的性质，极性溶剂中荧光光谱无精细结构，且荧光发射峰随介质极性的增加而红移。     

A Dual Emissive Coumarin–urea Derivative with an Electron-withdrawing Substituent in the Presence of Acetate Anion

We investigated the fluorescent properties, including the excited-state intermolecular proton transfer, of urea derivatives comprising a coumarin ring, which is a widely used fluorophore. We prepared two different coumarin–urea derivatives, 6CU and 7CU, which bear a urea-based substituent at the 6 and 7 positions of a coumarin ring, respectively. In the presence of the acetate ion, 7CU showed additional tautomer fluorescence emission with respect to 6CU, indicating that tautomer formation depends on the positions of the urea-based substituent on the coumarin ring. Thus, the resonance structures of urea derivatives might play an important role in the behavior of dual fluorescence, which is an important phenomenon applicable to photochemical anion sensing. Moreover, in order to further improve the fluorescence properties of the mentioned derivatives, a CF₃ group was introduced in a phenyl ring opposite to a coumarin ring. The fluorescence quantum yield of 7CUCF₃ thus synthesized was 65 times as large as that of 7CU, an observation that renders 7CUCF₃ a suitable anion sensor candidate. The results of this study will contribute to the development of new molecular designs for highly fluorescent sensing.     

1,3,5-Triaryl-1,3,5-Triazinane-2,4,6-Trithiones: Synthesis,Electronic Structure and Linear Optical Properties

The synthesis of four new 1,3,5-triaryl-1,3,5-triazinane-2,4,6-trithione derivatives (thioisocyanurates) and two new partially thionated analogues from the corresponding 1,3,5-triaryl-1,3,5-triazinane-2,4,6-triones (isocyanurates) is reported, together with their spectroscopic properties. DFT calculations and comparison with the corresponding isocyanurates evidence the impact of the oxygen-for-sulfur replacement on the electronic structure and linear optical properties of these heterocycles. A bathochromic shift of the absorption bands and more efficient quenching of the fluorescence was observed.     

Design and Synthesis of New 5-aryl-4-Arylethynyl-1H-1,2,3-triazoles with Valuable Photophysical and Biological Properties

Cu-catalyzed 1,3-dipolar cycloaddition of methyl 2-azidoacetate to iodobuta-1,3-diynes and subsequent Suzuki-Miyaura cross-coupling were used to synthesize new triazoles derivatives: 5-aryl-4-arylethynyl-1H-1,2,3-triazoles. Investigation of their optical properties by using UV absorption and fluorescence emission spectroscopies revealed that all molecules possess fluorescence properties with the values of the Stokes shift more than 100 nm. The photophysical behavior of the two most promising triazoles in polar and non-polar solvents was also studied.     

Synthesis and properties of quinazoline derivatives containing cymantrenyl group

The synthesis of new quinazoline derivatives with 2,3- and 4-positioned cymantrenyl fragment is described. Alkylation of 2-substituted quinazolin-4-ones with cymantrenylalkyl bromides on using K₂CO₃, potassium tert-butoxide, and sodium hydride as bases has been studied. It is established for the first time that condensation of 2-methylquinazolin-4-ones with aldehydes can cause elimination of the substituent at the nitrogen atom in position 3. The new cymantrene derivatives possess fluorescence properties.     

How a Small Structural Difference Can Turn Optical Properties of π‐Extended Coumarins Upside Down: The Role of Non‐Innocent Saturated Rings

The fluorescence properties of two new families of heterocycles possessing either a seven‐ or five‐membered ring attached at the core molecule are entirely different in solution and in the solid state. Crystallization has the effect of inhibiting non‐radiative excited‐state deactivation pathways, operative in solution for the seven‐membered ring compounds, thus leading to significant fluorescence efficiency in the solid state, with quantum yields ranging from 0.10 to 0.36. Conversely, the five‐membered ring derivatives, which display notable emission properties in solution, are almost non‐emissive in the crystalline state, characterized by a long‐range π‐stacked arrangement. When embedded in polymeric films, both series show fluorescence features similar to the solution case, with remarkable fluorescence quantum yields ranging from 0.09 to 0.41. According to quantum chemical calculations, 3H‐chromeno[3,4‐c]pyridine‐4,5‐diones show the specific mechanism of fluorescence quenching. The derivatives bearing the seven‐membered ring undergo, in solution, a significant structural deformation in the excited state, resulting in a large decrease of the energy gap between S₁ and S₀ and hence to a substantial contribution of the internal conversion in the relaxation process. The fluorescence quenching of the five‐membered ring derivatives is in turn related to the intermolecular interaction between adjacent molecules prevailing to a greater extent in the crystal lattice.     

Solid state fluorescence of Pigment Yellow 101 and derivatives: a conserved property of the individual molecules

The optical properties of the bisazomethine pigments Pigment Yellow 101 (P.Y.101) and three derivatives are investigated employing density functional theory (DFT) and time-dependent DFT (TDDFT). P.Y.101 and one of its derivatives exhibit unusual solid state fluorescence, although both possess OH groups and the latter pigment has particularly small intermolecular distances in its crystal, which are both properties that contradict common empirical rules for fluorescent pigments. Here it is shown that the OH groups are indeed essential for molecular fluorescence of the pigments due to the necessary formation of an intramolecular hydrogen bond with the lone pairs of the bisazomethine nitrogens. Furthermore, the quenching mechanism of molecular fluorescence in the non-fluorescent derivatives is analyzed in detail and a CNN bending motion of the central bisazomethine substructure is identified to be the relevant reaction coordinate along which efficient fluorescence quenching occurs in the individual molecule as well as in the crystal. Electron transfer quenching, which usually is expected to be an important quenching mechanism in aggregated media (here the crystals), is ruled out for the studied bisazomethine pigments. The solid state fluorescence properties of the pigments can finally be understood as conserved molecular properties of the individual pigment molecules.     

Photochromism of new 3,5-position hybrid diarylethene derivatives bearing both thiophene and thiazole moieties

Five new diarylethenes based on a hybrid structure of bis(5-thiazolyl)ethene and bis(3-thienyl)ethene were synthesized, and the structures of the four compounds were determined by single-crystal X-ray diffraction analysis. The properties of these diarylethenes, such as photochromism, fluorescence, and electrochemical properties were investigated in detail. All of these compounds showed good photochromism and fluorescence both in solution and in PMMA films. The electron-donating substituents could effectively increase the cyclization and cycloreversion quantum yields, and the fluorescence emission peaks, whereas the electron-withdrawing groups functionalized an inverse action for these diarylethene derivatives. Cyclic voltammetry revealed that great differences existed amongst the electrochemical behaviors of these compounds. The oxidation potentials and the band gaps of these diarylethenes increased remarkably with the increase in electron-withdrawing ability. All results suggested that the effects of substitution have a significant effect on the photochemical and electrochemical behaviors of these diarylethene derivatives.     

Chemical approaches for mimicking logic functions within fluorescent MPT dyes

The progress of the design, synthesis, fluorescence properties and application of a new family of fluorescent molecular switches towards information processing at the molecular level was reviewed. On the basis of the high fluorescence quantum yields and surroundings-sensitive fluorescent properties of the 5-methoxy-2-(2-pyridyl)-thiazole (2-MPT, 1) and a series of its derivatives as prepared, multiple binary logic and arithmetic functionalities were realized through encoding the controllable fluorescence switching properties with binary digit. Combined with the microfluidic platform, the fabrication of the molecular logic devices was attempted. Supported by the National Natural Science Foundation of China (Grant Nos. 20821091, 20705003 & 20733001) and Peking University Financial Support     

New fluorescent benzocrown ether derivatives of tetrathiafulvalene: facile synthesis and recognition properties

Two new fluorescent crown ether derivatives of tetrathiafulvalene (TTF) (2a and 2b) were synthesized and characterized; their electrochemical response to Na⁺ ions and fluorescence properties were investigated. The mechanism of the strong fluorescence has also been explored.     

DBD Dyes as Fluorescence Lifetime Probes to Study Conformational Changes in Proteins

Previously, [1,3]dioxolo[4,5‐f][1,3]benzodioxole (DBD)‐based fluorophores used as highly sensitive fluorescence lifetime probes reporting on their microenvironmental polarity have been described. Now, a new generation of DBD dyes has been developed. Although they are still sensitive to polarity, in contrast to the former DBD dyes, they have extraordinary spectroscopic properties even in aqueous surroundings. They are characterized by long fluorescence lifetimes (10–20 ns), large Stokes shifts (≈100 nm), high photostabilities, and high quantum yields (>0.56). Here, the spectroscopic properties and synthesis of functionalized derivatives for labeling biological targets are described. Furthermore, thio‐reactive maleimido derivatives of both DBD generations show strong intramolecular fluorescence quenching. This mechanism has been investigated and is found to undergo a photoelectron transfer (PET) process. After reaction with a thiol group, this fluorescence quenching is prevented, indicating successful bonding. Being sensitive to their environmental polarity, these compounds have been used as powerful fluorescence lifetime probes for the investigation of conformational changes in the maltose ATP‐binding cassette transporter through fluorescence lifetime spectroscopy. The differing tendencies of the fluorescence lifetime change for both DBD dye generations promote their combination as a powerful toolkit for studying microenvironments in proteins.     

四苯乙烯和三苯乙烯修饰的8-羟基喹啉聚集诱导发光特性研究

将2-甲基-8-羟基喹啉与四苯乙烯或三苯乙烯基团结合,合成了两种新型喹啉衍生物(4-Br-TPE-8HQ及TriPE-8HQ),并对其进行了光物理性能研究。结果发现,连接有四苯乙烯的喹啉衍生物能够体现聚集诱导发光(AIE)特性,而连接三苯乙烯的喹啉衍生物却显示温和的聚集诱导猝灭(ACQ)效应,实现了通过功能基团来调节目标分子聚集诱导效应的目的。研究发现,不同体系下分子的整体平面性有所不同,其中三苯乙烯修饰的衍生物在溶液中的荧光寿命(0.55 ns)高于固体荧光寿命(0.43 ns);循环伏安法证明两者具有良好的电化学稳定性,计算得到的4-Br-TPE-8HQ和TriPE-8HQ的LUMO能级分别为-2.40 eV和-2.43 eV,表明为两个化合物注入电子是可行的。     

Development of a highly specific rhodamine-based fluorescence probe for hypochlorous acid and its application to real-time imaging of phagocytosis

The tetramethylrhodamine (TMR) fluorophore is a useful platform for fluorescence probes, being applicable, for example, to biological investigations utilizing fluorescence microscopy, owing to its excellent photochemical properties in aqueous media. We have developed new TMR derivatives that show different dependences of their behavior upon the environment. Among them, HMTMR showed unique characteristics, and its putative spirocyclic structure was confirmed by X-ray crystallography. Utilizing this discovery, we have established a strategy to modulate the fluorescence of TMR by regulating the spirocyclization, and we have obtained a new fluorescence probe that can detect hypochlorous acid specifically. This probe, HySOx, can work in 99.9% aqueous solution at pH 7.4 and was confirmed to be able to detect hypochlorous acid being generated inside phagosomes in real time. HySOx is tolerant to autoxidation and photobleaching under bioimaging conditions. Regulation of the spirocyclization of rhodamines, as we describe here, provides a new approach to the rational development of novel fluorescence probes.     

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.     

Optimization of fluorescence property of the 8-oxodGclamp derivative for better selectivity for 8-oxo-2′-deoxyguanosine

2′-Deoxyguanosine (dG) suffers from oxidation by reactive oxygen species (ROS) to form 8-oxo-2′-deoxyguanosine (8-oxo-dG), which is regarded as a marker of oxidative stress in the cells. In our continuous study for the recognition molecule of 8-oxo-dG, 8-oxoGclamp and its derivatives have been identified as the selective fluorescent probe. However, it is an obstacle for further application that dG also forms a complex with 8-oxoGclamp, resulting in fluorescence quenching in less polar solvents. Quenching of the fluorescence of 8-oxoGclamp is thought to involve photo-induced electron transfer in the complex. It was hypothesized that the energy level of the excited state of 8-oxoGclamp and the HOMO energy of dG are the preliminary determinant of the quenching efficiency. Thus, fluorescence properties of the substituted derivatives at the 7-position of the 1,3-diazaphenoxazine part of 8-oxoGclamp were investigated. Among the new derivatives, fluorescence of the 7-phenyl substituted 8-oxoGclamp was not quenched by dG even in the stable complex, exhibiting the highest selectivity for 8-oxo-dG.     

4,5,9,10‐Pyrene Diimides: A Family of Aromatic Diimides Exhibiting High Electron Mobility and Two‐Photon Excited Emission

The design and synthesis of high‐performance n‐type organic semiconductors are important for the development of future organic optoelectronics. Facile synthetic routes to reach the K‐region of pyrene and produce 4,5,9,10‐pyrene diimide (PyDI) derivatives are reported. The PyDI derivatives exhibited efficient electron transport properties, with the highest electron mobility of up to 3.08 cm² V⁻¹ s⁻¹. The tert‐butyl‐substituted compounds (t‐PyDI) also showed good one‐ and two‐photon excited fluorescence properties. The PyDI derivatives are a new family of aromatic diimides that may exhibit both high electron mobility and good light‐emitting properties, thus making them excellent candidates for future optoelectronics.     

可聚合1,8-萘酰亚胺衍生物掺杂聚硅氧烷复合材料的合成及荧光特性

合成了3种可聚合的1,8-萘酰亚胺衍生物, 并研究了其在二甲基亚砜(DMSO)溶液中的光物理性质. 这些化合物表现出的光物理性质与其电子环境有关. 通过溶胶-凝胶法制备了可聚合1,8-萘酰亚胺衍生物与硅氧烷的共聚物. 尽管3种萘酰亚胺衍生物C-4位的取代基不同, 但在3-氨丙基三乙氧基硅烷(APTES)固凝胶中摩尔分数为0.06%时荧光强度均最大. 利用 ²⁹Si MAS NMR对合成材料进行了表征, 结果表明, 硅氧烷的缩聚程度影响材料的荧光强度, 说明材料中荧光单元的分子运动对材料的荧光性能有重要影响.