Synthesis and photophysical characterization of new fluorescent bis-amino acids bearing a heterocyclic bridge containing benzoxazole and thiophene

A series of new bis-alanine derivatives bearing (oligo)thiophene and benzoxazole units as the heteroaromatic bridge were synthesized in moderate to good yields. The photophysical characterization of these bis-amino acids was performed by UV-vis absorption and fluorescence emission studies and revealed that the compounds displayed exceptionally high fluorescence quantum yields, making them good candidates for application as fluorescent probes when incorporated into peptides, as well as peptide conformation-restricting and cross-linking elements.     

Heteroaromatic alanine derivatives bearing (oligo)thiophene units: synthesis and photophysical properties

A series of new benzoxazolylalanine derivatives bearing (oligo)thiophene units at the side chain were synthesized in good yields. The photophysical characterization of these amino acids was performed by UV-vis absorption and fluorescence emission studies and revealed that some of the compounds display high fluorescent quantum yields, making them good candidates for application as fluorescent probes.     

Synthesis of bis-ANS fluorescence probe in ionic liquids

A new application of ionic liquids in the preparation of fluorescence probe 5,5'-bis-8-phenylamino-l-naphthylsulfonate (bis-ANS) is represented. The method for the preparation of fluorescence probe bis-ANS in alkyl imidazolinm cationic liquids under acidic conditions is described. The effects on reaction yields under different concentration of sodium nitrite and different ionic liquid were studied and good yields were achieved.     

Synthesis of pyrido[2,3-b]indoles and pyrimidoindoles via Pd-catalyzed amidation and cyclization

Biologically and pharmaceutically active core structures containing a new class of 4-hydroxy-α-carbolines, dihydropyrido[2,3-b]indoles, pyrimido[4,5-b] and [5,4-b]indoles have been synthesized in good yields via Pd-catalyzed amidation and cyclizations. The keto-enol tautomerism in 4-hydroxy-α-carbolines has been investigated by DFT calculations and spectroscopic techniques. The fluorescence studies of pyrimido[4,5-b] and [5,4-b]indoles were carried out with good quantum yields.     

Synthesis of non-symmetrical alkynylpyridines by chemoselective Sonogashira cross-coupling reactions

4-Bromo-2,3,5-trichloro-6-iodopyridine was studied as a new substrate in chemoselective Sonogashira reactions. This approach provides an efficient access to non-symmetrical mono-, di-, tri- and pentaalkynylated pyridines in good yields. Selected pentaalkynylated pyridines were studied with regard to their UV/Vis- and emission properties showing moderate to high fluorescence quantum yields.     

含吡啶环的芳香醚-噁二唑类化合物的合成及其光谱研究

为开发新的高强度的有机电致发光材料, 用含烷氧基的取代苯甲酸(2)与2,6-吡啶二甲酰肼(3)在POCl3作用下, “一锅煮”法合成6个结构对称的含吡啶环的芳香醚-噁二唑4a～4f. 通过MS, IR, 1H NMR, 元素分析等手段对其结构进行了表征. 化合物的荧光性能测定结果显示此类化合物具有良好的荧光性, 其荧光发射波长均在347～507 nm范围内, 最大荧光发射波长在384 nm附近处, 且荧光强度较强. 在芳环上引入5-Br基团(4e, 4f), 化合物的荧光发射波长发生红移, 荧光强度有所减弱. 以硫酸奎宁作参比, 测定6个目标产物的荧光量子产率, 5-Br基团的引入对荧光量子产率没有明显影响. 同时讨论了代表性产物4a在不同溶剂中最大荧光激发波长处的荧光量子产率, 发现溶剂极性对该类化合物的荧光量子产率基本没有影响.     

Metal‐Free Facile Synthesis of Multisubstituted 1‐Aminoisoquinoline Derivatives with Dual‐State Emissions

Although isoquinoline is a good traditional fluorescent structural unit, most of its derivatives emit fluorescence in solution and a few of them can emit solid‐state fluorescence as well. Herein, a series of multisubstituted 1‐aminoisoquinoline derivatives were synthesized by a simple reaction of a readily available 4H‐pyran derivative and secondary amines. The reaction had advantages of metal‐free, mild conditions, simple operation, and good yields, which was realized by a ring‐opening and sequential ring‐closing mechanism. These 1‐aminoisoquinoline derivatives were found to exhibit interesting dual‐state emissions. In the solution, they emitted strong blue fluorescence at about 458 nm. In the solid state, they emitted solid‐state blue fluorescence at 444–468 nm with high fluorescence quantum yields of 40.3–98.1%. Crystal structural analyses indicated that solid‐state emissions of these compounds originated from twisted molecular conformations and the resultant loose stacking arrangements. Furthermore, their solid‐state fluorescence wavelengths were demonstrated to depend on molecular conformations rather than stacking arrangements. The discovery of these 1‐aminoisoquinolines with multiple reaction sites provides new possibilities for the development of solid‐state fluorescent materials based on the traditional isoquinoline skeleton.     

Synthesis and Spectral Characteristics of Novel Fluorescent Dyes Based on Pyrimido[4,5‐d] [1,2,4]triazolo[4,3‐a]pyrimidine

Different derivatives of a novel heterocyclic system, i.e., pyrimido[4,5‐d] [1,2,4]triazolo[4,3‐a]pyrimidine, are synthesized in moderate‐to‐good yields. These compounds exhibit excellent photochromism upon photoirradiation. The photophysical characterizations of these new compounds were evaluated by UV/VIS absorption and fluorescence emission studies. The emission spectra in various solvents are also presented and discussed. The changes are due to the intramolecular H‐bonding of pyrimido‐triazolo‐pyrimidine with H₂O, and photoinduced electron and general solvent effect. These compounds display high fluorescence quantum yields and are reported as new fluorophores.     

Novel peptidomimetic macrocycles showing exciplex fluorescence

The synthesis of five new chiral macrocyclic peptidomimetic naphthalenophanes, together with two open-chain derivatives, is described. The cyclization step is accomplished in good yields without the use of high dilution or template techniques. The new compounds have been photophysically studied by means of steady-state fluorescence spectroscopy. It has been found that the smaller the ring size, the higher the emission quantum yield from the excited charge-transfer state (CTS, exciplex) and the lower the fluorescence from the locally excited state (LES). The occurrence of exciplex fluorescence is noteworthy as the electron-donating groups are secondary amine moieties, which do not normally form emissive exciplexes.     

Syntheses of Novel Asymmetric Cyclopentanone Dyes and Measurement of Two－photon Absorption Cross－section

A simple synthesis route with a high yield of novel asymmetric cyclopentanone dyes 3a—3e and their highly two-photon up-converted fluorescences are reported. The dyes have good solubilities in most of ordi-nary solvents, a wide UV absorption wavelength range from 380—540 nm, and high fluorescence quantum yields. The two-photon absorption cross-sections of dyes 3a—M were measured in chloroform by a two-pho-ton induced fluorescence method. All of these properties of the new dyes make them suitable for being used as two-photon fluorescent probes.     

Solvent and central metal effects on the photophysical and photochemical properties of 4-benzyloxybenzoxy substituted phthalocyanines

The synthesis and characterization of new peripherally tetra-4-benzyloxybenzoxy substituted metal-free, zinc and lead phthalocyanines are described for the first time in this study. The influence of various organic solvents and the nature of the central metal ion on the spectroscopic, photophysical and photochemical properties has been investigated. General trends are described for photodegradation, singlet oxygen and fluorescence quantum yields, and fluorescence lifetimes of these compounds in different solvents. Photophysical and photochemical properties of phthalocyanine compounds are very useful for photodynamic therapy applications. Especially high singlet oxygen quantum yields are very important for Type II mechanism. The studied phthalocyanine compounds showed good singlet oxygen generation and these compounds show potential as Type II photosensitizers. The fluorescences of the studied compounds are effectively quenched by 1,4-benzoquinone in different solvents.     

Synthesis of Tripodal Naphthylacetamide Derivatives

A tripodal naphthylacetamide derivative (I and II) used as anew enhancement fluorescence chemical sensor for detection of transition metal ions has been synthesized in this work. Two new derivatives were prepared in good yields according to the proposed method. The products were characterized by elemental analysis, ¹H NMR spectra, and mass spectrometry (MS).     

Synthesis and photophysical properties of triphenylamine-based dendrimers with 1,3,5-triphenylbenzene cores

Two new conjugated dendrimers bearing a triphenylamine moiety as dendrons and 1,3,5-triphenylbenzene as a core have been synthesized through a convergent synthetic strategy. These conjugated dendrimers have high fluorescence quantum yields and exhibit similar absorption and emission behaviors in solutions and in solid films, which demonstrate that these dendrimers form good amorphous states.     

Development of excellent long-wavelength BODIPY laser dyes with a strategy that combines extending π-conjugation and tuning ICT effect

By comparison and combination of two strategies, extending π-conjugation and tuning Intramolecular Charge Transfer (ICT) effect, new long-wavelength BODIPY dyes have been efficiently synthesized. The new chromophores exhibit good optical properties: high fluorescence quantum yields, exceptionally large molar extinction coefficients, narrow red-emission bands, and relatively large Stokes shifts etc., in polar or apolar solvents. Besides, the new dyes, under transversal pumping at 532 nm, exhibit highly efficient and stable laser emission tunable from the green to NIR spectral region (570-725 nm). Moreover, one of these new BODIPY derivatives shows cell membrane permeability and bright intracellular red fluorescence. These advantageous characteristics assure the potential of these dyes for biophotonic applications.     

8-Alkenylborondipyrromethene dyes. General synthesis, optical properties, and preliminary study of their reactivity

A new series of 8-alkenylBODIPY dyes were prepared via the Liebeskind-Srogl cross-coupling starting from 8-thiomethyl-substituted BODIPY. Ten derivatives were prepared using alkenylboronic acids in good to excellent yields (79-97%), and one additional example was prepared from an alkenylstannane in 74% yield. The products display Michael acceptor-like reactivity. The alkenyl fragment quenches the fluorescence of the BODIPY core, which is turned back on by reducing the double bond.     

A mild high yielding synthesis of oxazole-4-carboxylate derivatives

Several 2,5-disubstituted oxazole-4-carboxylates were prepared in high yields from the methyl esters of N-acyl-β-halodehydroaminobutyric acid derivatives by treatment with a 2% solution of DBU in acetonitrile. The scope of this reaction was investigated and it was found that dehydrodipeptides having a β-bromodehydroaminobutyric acid residue gave the corresponding oxazoles in good yields. The photophysical properties of some of the oxazoles prepared were studied in four solvents of different polarity. All compounds have reasonable high fluorescence quantum yields and a moderate solvent sensitivity, which makes them good candidates to be used as fluorescent probes. One of the fluorescent oxazoles prepared was inserted after cleavage of the methyl ester into two model peptides using a conventional solution phase strategy. The photophysical properties of the labelled peptides were studied in ethanol and water and compared with those of the oxazole. The results obtained showed that the oxazole maintains a good fluorescence level and the same solvent sensitivity when linked to a peptide chain.     

Benzothiadiazole-based dyes that emit red light in solution,solid, and liquid state

In this paper, we report the preparation and red-light-emitting behavior of benzothiadiazole–tris(alkyloxy)phenylethene dyes. In solution, we observed an efficient red light emission with high fluorescence quantum yields (up to 0.78). With increase in solvent polarity, the emission bands shifted to longer wavelengths accompanied by a large Stokes shift of up to 152 nm. A moderate fluorescence quantum yield of 0.52 could be achieved even in the polar solvent dimethylformamide. Red light emission with good fluorescence quantum yields (up to 0.50) was also observed in the bulk solid, liquid, and film state.     

Novel peripherally substituted zinc phthalocyanine: synthesis,characterization, investigation of photophysicochemical properties and theoretical study

The new thiohexanoic acid substituted zinc phthalocyanine was synthesized and characterized by FT-IR, ¹H–NMR, electronic spectroscopy, and mass spectrometry as well as DFT calculation studies. The photochemical properties (singlet-oxygen quantum yields and photodegradation quantum yields) and photophysical properties (fluorescence quantum yields and fluorescence behavior) of the compound were studied in dimethylsulfoxide (DMSO), dimethylformamide (DMF) and tetrahydrofuran (THF). Singlet-oxygen quantum yields ranged from 0.29 to 0.43. However, energy-minimized structure, vibrational frequency, electronic distribution and molecular orbitals were obtained by DFT calculations which were supported by experimental results.     

Synthesis and properties of NIR aza-BODIPYs with aryl and alkynyl substituents on the boron center

NIR diaryl aza-borondipyrromethene dyes (C-aza-BODIPY) and dialkynyl aza-borondipyrromethene dyes (E-aza-BODIPY) were synthesized from difluoro aza-borondipyrromethene dyes (F-aza-BODIPY) in 45-83% yields. By X-ray analysis the N-B distances (1.603 and 1.606 Å) in C-aza-BODIPY were found to be longer than the corresponding bond of C-BODIPY by 0.02-0.04 Å. C-aza-BODIPYs display remarkable blue shifts and low fluorescence quantum yields, and E-aza-BODIPYs have moderate fluorescence quantum yields (0.16-0.29). C- and E-aza-BODIPYs display good stability in weak acidic and basic conditions. E-aza-BODIPY was dialytic and suitable to staining of living cells.     

Enhanced Solution and Solid-State Emission and Tunable White-Light Emission Harvested by Supramolecular Approaches

Organic luminescent materials with high quantum yields and/or white-light-emitting properties in particular play a crucial role in labeling and optoelectronic devices. In this work we have synthesized a new 2,3,6,7-tetramethoxy-9,10-di-p-tolylanthracene-bridged pillar[5]arene dimer with persistent mazarine blue fluorescent emission and much higher quantum yields in both solution and the solid state in comparison with its corresponding emissive linker without pillarene units, which exhibits typical aggregation-caused quenching. According to the fluorescence data and single-crystal analyses, their contrasting fluorescent performances can be rationally ascribed to their different stacking structures and intermolecular interactions. Three fluorescent guests containing different chromophores and/or terminal binding sites have also been synthesized to interact with the pillar[5]arene dimer to construct supramolecular ensembles with highly controllable luminescence, taking advantage of the stimuli-responsive properties of the supramolecular host–guest interactions. Intriguingly, multicolor fluorescence, including white-light emission (0.31, 0.35), which is in high demand, has been achieved by tuning the molar ratio of the host and guest and/or by changing the solvent system. This strategy holds great potential for the design and development of fluorescent materials with high quantum yields, controllable emission wavelength, and good stimuli-responsiveness.