Amplified fluorescence quenching of a conjugated polyelectrolyte mediated by Ca2+

The fluorescence of conjugated polyelectrolytes (CPEs) is quenched with very high efficiency by small molecule quenchers. This effect has been referred to as amplified quenching. In the present communication, we demonstrate that aggregation of a poly(phenylene ethynylene)-type CPE (PPE-CO2-) induced by Ca2+ has a pronounced effect on the amplified quenching of the polymer by the dication methyl viologen (MV2+). In particular, absorption and fluorescence spectroscopy of PPE-CO2- in methanol solution indicate that addition of a low concentration of Ca2+ induces aggregation of the polymer chains. The range of MV2+ concentrations within which linear Stern-Volmer quenching behavior is observed systematically decreases with increasing Ca2+ concentration to a point where superlinear quenching is observed immediately upon addition of MV2+. This finding is unequivocal evidence that the superlinear Stern-Volmer quenching behavior typically observed in CPE-quencher systems arises due to quencher-induced aggregation of the CPE chains.     

Luminescence quenching of a phosphorescent conjugated polyelectrolyte

The photophysical and luminescence quenching properties of a platinum(II) acetylide-based conjugated polyelectrolyte, Pt-p, which features carboxylic acid solubilizing groups are reported. The Pt-acetylide polymer is water soluble, and it exhibits phosphorescence from a triplet pi,pi exciton based on the conjugated backbone. The phosphorescence from Pt-p is quenched by viologens with different charges (MV(+), MV(2+), and MV(4+)), and in each case the quenching is dominated by a dynamic (diffusional) mechanism. Comparison of the Stern-Volmer quenching properties of Pt-p with those of a structurally analogous fluorescent organic polyelectrolyte leads to the conclusion that the amplified quenching effect, which is commonly observed for fluorescent conjugated polyelectrolytes, is not important for the platinum acetylide phosphorescent conjugated polyelectrolyte.     

Amplified quenching in metal-organic conjugated polymers

The luminescence from conjugated polyelectrolytes that contain pendant metal complex units is quenched very efficiently by oppositely charged electron acceptors.     

Structural and environmental requirements for quenching of singlet oxygen by cyanine dyes

Singlet-oxygen quenching constants were measured for 19 cyanine dyes in acetonitrile. The most efficient quenchers were 1-butyl-2-[2-[3-[(1-butyl-6-chlorobenz-[cd]indol-2(1H)- ylidene)ethylidene]-2-chloro-1-cyclohexen-1-yl]ethenyl]-6-chlorobenz[cd] indolium and 6-chloro-2-[2-[3-(6-chloro-1-ethylbenz[cd]indol-2(1H)-ylidene) ethylidene]-2-phenyl-1-cyclopenten-1-yl]ethenyl]-1-ethyl-benz[cd]indolium, having quenching constants with diffusion-controlled values of 2.0 +/- 0.1 x 10(10) and 1.5 +/- 0.1 x 10(10) M-1 s-1, respectively. There was a trend toward increased quenching constants for cyanine dyes with the absorption band maxima at longer wavelengths. However, the quenching constants correlated better with the oxidation potentials of the cyanine dyes, suggesting that quenching proceeds by charge transfer rather than energy transfer. The quenching constants for 1,1',3,3,3',3'-hexamethylindotricarbocyanine perchlorate and 1,1'-diethyl-4,4'-carbocyanine iodide were measured in several solvents as well as in aqueous solutions of detergent micelles. In different solvents, the quenching constants varied by as much as a factor of 50. The quenching constants were largest in solvents with the highest values on the pi* scale of Kamlet, Abboud, Abraham and Taft. This was consistent with quenching occurring by charge transfer. Within cells, cyanine dyes concentrate in membrane-bound organelles. The quenching constants were substantial within detergent micelles. To the extent that micelles are models for biological membranes, cyanine dyes may be effective biological singlet-oxygen quenchers.     

Amplified fluorescence quenching and biosensor application of a poly (para-phenylene) cationic polyelectrolyte

The quenching behavior of a water-soluble cationic poly (para-phenylene) bearing quaternized ammonium side groups (P-NEt ₃ ⁺ ) was studied. P-NEt ₃ ⁺ is efficiently quenched by sodium anthraquinone-2,6-disulfonate (AQS) and sodium 1,4,5,8-naphthalenediimide-N,N’-bis (methylsulfonate) (NDS) in aqueous solution via a photo-induced electron-transfer mechanism. Absorption spectra of the NDS/P-NEt ₃ ⁺ ion-pair complex indicated formation of a stable charge-transfer complex in the ground state. A large spectral shift and band broadening occurred during AQS/P-NEt ₃ ⁺ complex formation, which is believed to arise due to P-NEt ₃ ⁺ conformational changes induced by hydrophobic interactions. Finally, a protein sensor that relies on the quenching behavior of P-NEt ₃ ⁺ was designed based on the quencher-tether-ligand (QTL) approach. AQS tethered to biotin (AQS-E-Biotin) was used along with P-NEt ₃ ⁺ to sense avidin.     

J-aggregation of cyanine dyes by self-assembly

The importance of highly ordered surfaces, containing adsorptive surface states, is discussed for J-aggregation by self-assembly. Such nucleating surfaces are nanometer-sized edges and corners of cubic AgBr microcrystals, or surface iodide-clusters located along edges and corners of AgBr:I microcrystals. Of particular interest are dendrimers, monoatomic steps on terraced silver halide microcrystals and fullerene derivatives as nucleating surfaces. Molecular organisation into J-aggregates by self-assembly was realized using aprotic, apolar solvents for fullerenes, and polar solvents for dendrimers and monoatomic surface steps. By using dendrimers as nucleating agents in mesopores of metal oxide nanoparticle coatings, size-controlled and stable J-aggregates with high optical densities and strong fluorescence were obtained reproducibly. Such films may be useful for sensors, opto-electronics, lighting and photovoltaics.     

Phosphorescence quenching by conjugated polymers

Energy transfer between phosphors and conjugated polymers was investigated using a fluorene trimer (F3) as a model conjugated material. The phosphors studied were bis-cyclometalated iridium complexes (FP, PPY, BT, PQ, and BTP), with triplet energies of 2.6, 2.4, 2.2, 2.1, and 2.0 eV, respectively (based on phosphorescence spectra). Stern-Volmer analysis of luminescent quenching shows that energy transfer from either FP or PPY to F3 is an exothermic process with Stern-Volmer quenching constants (kqSV) of near 109 M-1 s-1 while energy transfer from BT, PQ, and BTP is endothermic (kqSV = 107-106 M-1 s-1). On the the basis of above results, the triplet energy of F3 is estimated to be less than 2.3 eV (530 nm). This study suggests that conjugated polymers, which typically have lower T1 energies than F3, should also quench phosphorescent emission in thin films and organic light-emitting diodes (OLEDs) incorporating these and related phosphorescent dopants.     

Functionalization of near-infrared cyanine dyes

An indolium heptamethine cyanine dye 11 containing an isothiocyanate function for selective coupling of the dye chromophore with a primary amino group of proteins has been synthesized. Functionalization of a benzothiazolium heptamethine cyanine 12 is discussed.     

方酸菁染料的合成

方酸菁染料业经证明具有光谱增感作用,但迄今未见其作为照相材料应用的报道.1973年法国Siegfried等将其用于巨脉冲红宝石激光的无源切换;最近Morel等又研究了它们在太阳能电池中的应用.作者合成了八个方酸菁染料,并对它们的照相性能和光电转换特性作了初步研究;发现其中的个别化合物不但具有良好的光谱增感作用,而且与照相工业中常用的染料“1833”相比,衰退也比较慢;部分化合物还表现出相当高的光电转换效率. 作者曾报道方酸的合成.本文介绍另一种方法,即以醋酸钠-醋酸环化1,1,3-三氯-2,     

Photonics of dimers of cyanine dyes

The results of study on the properties of dimers of thiamonomethine-and thiatrimethinecyanines (thiacarbocyanines) in the ground and electronically excited states in aqueous solutions are presented. Dimers of cyanine dyes have the sandwiched structure with near-parallel alignment of the polymethine chains of the monomers in the dimer. The formation of dimers is manifested by two absorption bands of different intensities due to splitting of the S* level of the monomers upon their resonance interaction. Dimers of thiacarbocyanines are characterized by a low fluorescence quantum yield φ_fl as compared to monomers; however, φ_fl of dimers of thiamonomethinecyanines are markedly higher than that of monomers. Dimers of cyanine dyes are also characterized by a relatively high quantum yield of intersystem crossing to the triplet state. In the triplet-triplet absorption spectra, two bands of different intensities are revealed, which are due to the splitting of the higher triplet level of the monomers that form the dimer. In the presence of electron donors (ascorbic acid, hydroquinone) and/or acceptors (p-benzoquinone, p-nitroacetophenone, methylviologen), the triplet state of dimers is quenched as a result of electron transfer yielding radical products. Dimers in the triplet state can serve as photosensitizers of redox reactions.     

Specific search for heterocycles for cyanine dyes by means of a computer

A method for the selection by means of a computer of terminal heterocyclic groups for cyanine dyes that absorb over a predesignated spectral range is described. New monoazaheterocycles, the introduction of which into the compositions of cyanine dyes as terminal groups should ensure absorption in the near-IR region of the spectrum, are presented as examples.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 217–222, February, 1984.     

冠醚菁染料的研究VI.含苯并咪唑环的冠醚菁染料的合成

Cyanine dyes containing benzimidazolyl crown ether derivative groups were prepared and characterized by UV, IR, and NMR spectroscopy.     

Kinetics of salt-induced J-aggregation of cyanine dyes

The addition of monovalent, divalent, and trivalent metal ions to three anionic ethyl meso-thiacarbocyanine dyes, an ethyl meso-oxacarbocyanine, and an imidacarbocyanine in aqueous solution at room temperature results in the production of J-aggregates within the range of tens to hundreds of seconds. The rate of formation of J-aggregates correlates with the rate of decay of dimers or monomers and is dependent on the type of metal ion, dye structure, and temperature. The rate of formation of J-aggregates increases as the temperature decreases and the dye and salt concentrations increase, and the rate is highest for trivalent ions and smallest for monovalent ions, independent of the type of anion. The time course of formation of J-aggregates is described in most cases by a sigmoidal curve, and the kinetics and mechanism are discussed within the framework of autocatalysis. Computer simulations reveal that the sigmoidal time dependence is transferred to an exponential-like curve by substantially increasing the rate constant for the noncatalytic step. The reaction pathway into J-aggregates can be switched from dimeric ion pairs as the reactant to monomeric ion pairs, when the rate constant for the catalytic step via the monomer becomes larger with respect to that via the dimer.     

Biocidal activity of a light-absorbing fluorescent conjugated polyelectrolyte

Herein we describe studies that indicate a cationic conjugated polyelectrolyte shows biocidal activity against gram-negative bacteria (Escherichia coli, E. coli, BL21, with plasmids for Azurin and ampicillin resistance) and gram-positive bacterial spores (Bacillus anthracis, Sterne, B. anthracis, Sterne). These studies were carried out with aqueous suspensions of the conjugated polyelectrolyte, with the polyelectrolyte in supported formats and with samples in which the conjugated polyelectrolyte was coated on the bacteria. The results are interesting in that the biocidal activity is light-induced and appears effective due to the ability of the conjugated polyelectrolyte to form a surface coating on both types of bacteria. The effects observed here should be general and suggest that a range of conjugated polyelectrolytes in different formulations may provide a useful new class of biocides for both dark and light-activated applications.     

冠醚苯并恶唑菁染料的合成

本文报道含冠迷苯并恶唑菁染料及半菁染料的合成,采用一种简便方法合成了关健中间体2-甲基6,7-二羟基苯并恶唑:从2,3,4-三羟基苯乙酮肟经beckmann重排而得到,将它再与三甘醇或四甘醇二氯化物反应 ,分别得到相应的冠醚化合物:2-甲基-6,7-并(12-冠-4)苯并恶唑和2-甲基-6,7-并(15-冠-5)苯并恶唑,将它们制成相应的季铵盐 ,然后分别与原甲酸乙酯或对二甲胺基甲醛作用,得到相应的冠醚恶唑菁染料,或半菁染料.     

High-efficiency fluorescence quenching of conjugated polymers by proteins

The fluorescence of the water-soluble anionic conjugated polymer, poly[lithium 5-methoxy-2-(4-sulfobutoxy)-1,4-phenylenevinylene] (MBL-PPV), is quenched in dilute aqueous solution by cytochrome c, a small, naturally occurring electron-transfer protein. The large value obtained for the Stern-Volmer constant (K(sv) = 3.2 x 10(8) at pH 7.4, and approximately 10(9) in acidic solutions) is attributed to a combination of two factors: (1) facile ET between the luminescent semiconducting polymer and the protein and (2) the Columb attraction between the oppositely charged polyelectrolytes. This system shows significant potential for biosensor applications.