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Although it has been reported ina few instances that the spectroscopicproperties of cyanine dyes were strongly dependent on the nature ofthe chemical substitution of their central carbon atom, there hasnot been to date any systematic study specifically aimed at rationalizingthis behavior. In this article, such a systematic study is carriedout on an extended family of 17 polymethine dyes carrying differentsubstituents on their central carbon, some of those being specificallysynthesized for this study, some of those similar to previously reportedcompounds, for the sake of comparison. Their absorption properties,which spread over the whole visible to near-infrared spectral range,are seen to be dramatically dependent on the electron-donating characterof this central substituent. By correlating this behavior to NMR spectroscopyand (vibronic) TD-DFT calculations, we show that it results from aprofound modification of the ground state electronic configuration,namely, a progressive localization of the cationic charge on the centralcarbon as the electron-donating nature of the central substituentis increased. [ABSTRACT FROM AUTHOR]

Highlights: [•] We report on the synthesis of two new IR range merocyanine dyes. [•] Photovoltaic properties of P3HT–PCBM–dye system depend on the dye concentration. [•] New physical phenomenon of photo-induced current hysteresis is reported. [•] Observed photoresistance behavior can be connected to polar properties of the dyes. [Copyright &y& Elsevier]

Highlights: [•] An anionic polymethine dye is incorporated in model bicationic vesicles/micelles. [•] In colloidal structures, absorption spectra detected dye monomers and H-aggregates. [•] In the presence of the lipid DDAB, H-aggregates slowly disaggregated into monomers. [•] A mechanism for the above disaggregation was proposed from kinetic/absorption data. [•] The dye sensed the exchanging dynamics of surfactant(s) between colloids and water. [ABSTRACT FROM AUTHOR]

Anionic polymethine dyes were obtained from fluorene equipped with electron-withdrawing groups (SOOCH(CF)CHF in positions 2 and 7 and NO in positions 4 and 5). Their electronic absorption spectra in various solvents were examined and compared with the spectra of related dyes derived from tetranitrofluorene and bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9 H-fluorene-2,7-disulfonate. The ab initio quantum chemical calculations (DFT and TDDFT at the B3LYP/6-31G(d,p) level of theory) were used to analyze the nature of electron transitions and the orbitals involved as well as the electron density redistribution in the excited state. [ABSTRACT FROM AUTHOR]

Highlights: [•] Polymethine dyes producing delocalized and local molecular orbitals have been investigated. [•] The local orbitals are characterized by the charge mainly localized within the terminal groups. [•] Their existence leads to a generation of the specific quasi-local electronic transitions. [•] They differ from the transitions between delocalized orbitals by sensitivity to the chain length. [•] The quasi-local transitions can be experimentally detected by absorption or anisotropy spectra. [Copyright &y& Elsevier]

A detailed investigation of the steady-state and time-resolved spectral properties of new cationic asymmetrical trimethine cyanine dye with indolenine and benzoimidazole terminal groups has been performed in comparison with its symmetrical analogues. Steady-state measurements included absorption, fluorescence, excitation anisotropy in several solvents of different polarity and viscosity. Kerr-gated time-resolved study of the fluorescence properties has been performed using 1кHz femtosecond laser system. Experimental results are in agreement with DFT/6-31(d,p)/B3LYP quantum chemical calculations, allowing determination of the charge distribution, bond length alternation, permanent and transition dipole moments, energy levels and the leading molecular orbital configurations responsible for the lowest electronic transitions. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Merocyanines with different electronic asymmetry were studied by ns-laser photolysis. [•] Lifetime and spectral shift regularities of merocyanines photoisomers are revealed. [•] DFT calculation of merocyanines structure and rotation barriers was carried out. [•] Polymethine chain C C bonds involved into photoisomerization are determined. [•] T–T-absorption and photostability of merocyanines were discussed. [Copyright &y& Elsevier]

The spectral and luminescent properties of film composites based on photoconductive poly-N-epoxypropylcarbazole (PEPC) and electrically neutral polyvinylbutyral (PVB) with admixtures of polymethine dyes with various ionicities are studied. The external magnetic field effect on the spectral and luminescent properties of film composites based on PEPC with cationic polymethine and merocyanine dyes is studied. The magnetic field effect in the photogeneration of electron-hole pairs is explained by the participation of the singlet–triplet intersystem crossing of excited dye molecules. [ABSTRACT FROM PUBLISHER]

Binary colloids of inorganic nanosheets prepared by exfoliation of two different layered crystals form phase-separated structures with demixing of the two nanosheets. The phase-separated colloids of photocatalytic niobate and photochemically inert clay nanosheets exhibit unusual photochemical reactions based on the phase-separated structure. The present paper reports photocatalytic decomposition of a cyanine dye in this binary colloid, where the dye is selectively adsorbed on the clay nanosheets to be spatially separated from the photocatalytic nanosheets. Upon UV irradiation, the dye is photocatalytically decomposed in the colloids containing the niobate nanosheets, but self-photolysis of the dye is observed in the colloid lacking the photocatalytic nanosheets. Faster decomposition in nitrogen than in air suggests contribution of the conduction-band electrons generated in the niobate nanosheets to the photocatalytic reaction. In the binary colloid, the degradation is retarded compared with the single-component niobate colloid. Larger clay content more stabilized the dye against the decomposition. In contrast, irradiation of the colloids with visible light causes self-photolysis of the dye even in the presence of the niobate nanosheets, indicating the absence of electron transfer from the photoexcited dye to the photocatalytic nanosheets. [ABSTRACT FROM AUTHOR]

Organic materials possess many keyattributes that make them suitable for exploitation in all-opticalsignal processing applications including facile tunability of theiroptical properties, strong and ultrafast nonlinear optical response,and potential for integration into device structures. In this perspective,we present molecular design guidelines for organic chromophores thatcould serve as the active constituents for such materials. Using arelatively simple model, a candidate class of chromophores, namelycyanine-like polymethines, is identified based on promising microscopicnonlinear optical properties in the near-IR spectral region. The challengesassociated with translating these microscopic properties into materialswith macroscopic properties suitable for device applications are presentedalong with molecular engineering approaches for overcoming these hurdles. [ABSTRACT FROM AUTHOR]

Quantitative structure activity relationship (QSAR) studies were performed on a set of polymethine compounds to develop new fluorescent probes for detecting amyloid fibrils. Two different approaches were evaluated for developing a predictive model: part least squares (PLS) regression and an artificial neural network (ANN). A set of 60 relevant molecular descriptors were selected by performing principal component analysis on more than 1600 calculated molecular descriptors. Through QSAR analysis, two predictive models were developed. The final versions produced an average prediction accuracy of 72.5 and 84.2% for the linear PLS and the non-linear ANN procedures, respectively. A test of the ANN model was performed by using it to predict the activity, i.e., staining or non-staining of amyloid fibrils, using 320 compounds. The five candidates whose greatest activities were selected by the ANN model underwent confirmation of their predicted properties by empirical testing. The results indicated that the ANN model potentially is useful for facilitating prediction of activity of untested compounds as dyes for detecting amyloid fibrils. [ABSTRACT FROM AUTHOR]

Molecularphotoisomerization plays a crucial role in diverse biologicaland technological contexts. Here, we combine ion mobility spectrometryand laser spectroscopy to characterize the photoisomerization of molecularcations in the gas phase. The target molecular ions, polymethine dyecations 3,3′-diethylthiacarbocyanine (DTC+), arepropelled through helium buffer gas by an electric field and are photoisomerizedby light from a tunable laser. Photoexcitation over the 450–570nm range converts trans-DTC+to cis-DTC+, noticeably modifying the ions’arrival time distribution. The photoisomerization action spectrum,which has a maximum at 535 nm, resembles the absorption spectrum ofDTC+in solution but is shifted 25 nm to shorter wavelength.Comparisons between measured and calculated mobilities suggest thatthe photoisomer involves a twist about the second C–C bondin the methine chain (8,9-cisisomer) rather thana twist about the first methine C–C bond (2,8-cisisomer). It is postulated that the excited gas-phase ions internallyconvert from the S1Franck–Condon region to theS0manifold and explore the conformational landscape asthey cool through He buffer gas collisions. Master equation simulationsof the relaxation process in the S0manifold suggest thatthe 8,9-cisisomer is preferred over the 2,8-cisisomer because it lies lower in energy and because itis separated from the transisomer by a substantiallyhigher barrier. The study demonstrates that the photoisomerizationof molecular ions can be probed selectively in the gas phase, providinginsights into photoisomerization mechanisms and information on thesolvent-free absorption spectrum. [ABSTRACT FROM AUTHOR]

Im Polymer eingeschlossen: Ein hydrophobes organisches Molekül, das im Nahinfrarot II (NIR ‐ II) fluoresziert, wurde durch den Einschluss in polymere Nanopartikel wasserlöslich und biokompatibel. Die Nanopartikel wurden mit hydrophilem Polyethylenglycol modifiziert; sie zeigten Fluoreszenz in der NIR ‐ II ‐ Region und gute Photostabilität in wässriger Umgebung und wurden zur In ‐ vivo ‐ Bildgebung in Mäusen verwendet. [ABSTRACT FROM AUTHOR]

Highlights: [•] Combining TD-DFT and two-state SOS approach to calculate the static γ. [•] Providing strategies to enhance χ (3) in non-centrosymmetric cyanine dyes. [•] Utilizing electron density difference to study the charge transfer properties. [ABSTRACT FROM AUTHOR]

One of the most important characteristics of polymethine dyes is their strong absorption in the ultraviolet, visible and near infrared regions. These properties also enable their use in many areas other than colouring. In this study, the preparation of chloro heptamethine cyanine as a type of polymethine dye was prepared. The preparation was carried out in the solution of quaternary ammonium salt and bisaldehyde in a controlled manner through heating under reflux. The product was characterized by determinations of its molecular weight, melting point, fluorescence, excitation and absorption properties. After wards, the suitability of the product on dye laser was investigated. Dye laser system was performed and, as expected, it was shown that the dye could produce laser light in the intervals where it shows its fluorescence property. [ABSTRACT FROM AUTHOR]

Abstract: We have prepared poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH–PPV) using a modified procedure and purified a number of times in each step. The results show that the MEH–PPV synthesized by the present technique offers low molecular weight and high thermal stability, which are some of the most important requirements for the fabrication of photo luminescent devices. The thermal diffusivities of MEH–PPV dissolved in different organic solvents were calculated for different concentrations. As the concentration was increased thermal diffusivity was decreased. The variation of thermal diffusivities with concentration and the calculated values at a particular concentration are varied in all organic solvents we used. The aggregates formed in the solution also affected the thermal diffusivity. Our studies show that thermal diffusivity of MEH–PPV is highly dependent on the characteristics of the solvent. [Copyright &y& Elsevier]

It was found that film composites based on carbazolyl-containing cooligomer with additions of cationic polymethine dyes exhibit photovoltaic characteristics in the absorption region of the dyes. If the length of the polymethine chain is reduced the value of the photovoltaic response is increased as a result of decrease in the energy of the highest occupied orbital of the dye molecule. In samples of the composite films with free surface area the photovoltaic effect is determined by diffusion of the more mobile positive carriers (the Dember effect) and by their recombination time. [ABSTRACT FROM AUTHOR]

Abstract: Both symmetrical anionic polymethine dye which is derived from the boron difluoride form of the dipyrromethene (BODIPY) and the corresponding symmetrical cationic dye derived from the cationic form of the dipyrromethene have been obtained on the identical atomic framework. Their spectral properties and π-electronic structure suggest that these long-wavelength absorbing dyes are closely related. On the contrary, the non-symmetrical compounds belong to the different types of dyes, namely merocyanines in the case of boron dipyrromethene complexes, and non-symmetrical cationic dyes for salt-like compounds. Each of these types possesses a distinct complex of spectral properties. [Copyright &y& Elsevier]

Syntheses are reported for di-, tetra-, and hexamethine merocyanines derived from 2,4,5,7-tetra-nitrofluorene and heterocyclic fragments with various electron-donating ability. The absorption spectra of these compounds were studied in solvents of different polarities. A quantum-chemical analysis was carried out for the electronic structure and types of electronic transitions of these merocyanines by using the DFT and TDDFT methods in the B3LYP/6-31G(d,p) basis set. The electronic structure of these merocyanines varied from neutral polyene to polymethine and bipolar polyene with increasing electron-donating ability of the heterocyclic fragment and with solvent polarity. These differences were strongly reflected in the position, intensity, and shape of the absorption bands, vinylene shifts, and deviations, as well as the sign of solvatochromic effect. [ABSTRACT FROM AUTHOR]

Thermal polymerizability of methyl methacrylate solution was examined in dimethylformamide in the presence of cationic symmetric and asymmetric polymethine dyes with different terminal electron-donating groups by dilatometric method. It was found that the polymethine dyes according to the electronic structure can initiate or inhibit the polymerization of methyl methacrylate both in the presence of standard initiator, azoisobutyronitrile, and in its absence by a radical mechanism. It was shown that the initiating ability was weakened with altering an electron-donating activating ability of terminal groups of dyes from the average level in both directions of its increasing or decreasing. The transition from symmetric to asymmetric dyes in the same structural type is accompanied by a loss of initiating ability. Based on the comparison of experimental kinetic data of polymerization of methyl methacrylate in the presence of dyes and quantum chemical calculations of electronic structure for dyes it was demonstrated that a HOMO energy value of an initiating dye must be higher and that of an inhibiting dye, lower than the methyl methacrylate value. [ABSTRACT FROM AUTHOR]

The external magnetic field effects on the spectral and luminescent properties of film composites based on photoconductive poly( N-epoxypropylcarbazole) doped with cationic polymethine and merocyanine dyes have been studied. The magnetic field effects on the intensity and kinetics of delayed fluorescence and recombination luminescence have been revealed. These effects are explained by participation in the photogeneration of charged pairs of singlet-triplet intersystem crossing in excited dye molecules. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of 2-methylbenzo[1,3]oxazine with julolidine-9-carbaldehyde under acid catalysis afforded an highly coloured blue dye with an intense absorption at 591 nm. NMR and UV–Vis analysis showed that this compound has an opened oxazine structure with a polymethine-type chromophore, corresponding to a protonated thermally stable coloured form of photochromic benzo[1,3]oxazines that are known to be unstable at room temperature with lifetimes in the ns timescale. In basic medium this dye is converted into a stable opened zwitterionic form of photochromic benzo[1,3]oxazines with two absorption maxima at 410 and 587 nm assigned to conjugated 3H-indolium and 4-nitrophenolate chromophores respectively. [Copyright &y& Elsevier]

We report that the cyanine dye Cy5 and several of its structural relatives are reversibly quenched by the phosphine tris(2-carboxyethyl)phosphine (TCEP). Using Cy5 as a model, we show that the quenching reaction occurs by 1,4-addition of the phosphine to the polymethine bridge of Cy5 to form a covalent adduct. Illumination with UV light dissociates the adduct and returns the dye to the fluorescent state. We demonstrate that TCEP quenching can be used for super-resolution imaging as well as for other applications, such as differentiating between molecules inside and outside the cell. [ABSTRACT FROM AUTHOR]

Abstract: Photochemical processes (photoisomerization and generation of the triplet state) of the thiacarbocyanine dyes 3,3′,9-trimethylthiacarbocyanine iodide (Cyan 2), 3,3′-diethyl-9-methylthiacarbocyanine iodide (DMTC), and 3,3′,9-triethylthiacarbocyanine iodide (TETC) in complexes with biomacromolecules—DNA and chondroitin-4-sulfate—were studied by flash photolysis. It has been shown that, along with generation of the triplet state, enhancement of the photoisomer formation is observed for Cyan 2 and DMTC complexed with the biomolecules. This effect can be explained by the influence of the biopolymer matrix on the potential energy curves of the photoisomerization process. [Copyright &y& Elsevier]

Abstract: A comprehensive quantum chemical analysis along with spectral-luminescence measurements has been performed for a new series of 2-azaazulene dyes with different conjugation lengths (n) to better understand the nature of their electronic transitions. The remarkably large red shift of their main absorption bands at relatively small n is connected with the existence of totally delocalized HOMO and LUMO. Symmetry breaking is observed experimentally at n =3 in polar solvents and theoretically at n =5 in vacuum. Analysis shows the existence of two types of molecular orbitals (MOs): local with the charge mainly localized within the terminal groups, and delocalized with the charge distributed throughout the molecule. Correspondingly, three types of electronic transitions are present: between delocalized MOs; between one local and one delocalized MO, and between local MOs only, which is important for predicting the positions of electronic transitions to the chain length. [Copyright &y& Elsevier]

In this high-technology application, age functional dyes especially polymethine dyes have captured much attention of the researchers due to their immense potential for high-tech uses. Polymethine dyes show promising absorption spectra in the visible range, which can be easily exploited for the use of written text copying, photographic imaging, or photothermographic recording materials. Keeping this in mind, our research is composed of an investigation of two triphenylamino-based polymethine dyes, a known polymethine dye 3 and a new one polymethine dye 5, which have been synthesized by the reaction of 4-(diphenylamino) benzaldehyde 2 and 4,4'-(phenylazanediyl) dibenzaldehyde 4 with 4,4'-vinylidene-bis(N, N-dimethylaniline) 1. Based on bis-dimethylaminophenylethylene moiety, the new polymethine dye showed more high absorption spectra in the range of 600-700 nm than that of the known polymethine dye based on bis-dimethylaminophenylethylene moiety. Their maximum spectra were exhibited at 637 nm and 653 nm, respectively. Their leuco-converted reversible colored forms were also investigated. [ABSTRACT FROM AUTHOR]

The spectral and luminescent properties of film composites based on photoconductive poly-N-epoxipropylcarbazole and nonphotoconductive polyvinylbutyral with admixtures of cationic and anionic polymethine dyes, as well as the effect of an external magnetic field on these properties, are studied. It is found that the magnetic field affects the intensity and kinetics of the delayed fluorescence and recombination luminescence of the cationic dye in photoconductive films. This is explained by specific features of photogeneration of charge pairs, namely, by the participation of the singlet and triplet excited states of dye molecules in this process, as well as by the singlet-triplet conversion in dye molecules and photogenerated charge pairs. [ABSTRACT FROM AUTHOR]

Extinction spectra of a hybrid material comprised of molecular layers of polymethine dyes and granulated silver films preliminarily deposited onto sapphire substrates are studied experimentally. Specific features of the dye layer composition and broadening of plasmon absorption bands are discussed. In hybrid samples, both an increase and a decrease in the silver-nanoparticle plasmon resonance frequency upon spreading of dyes have been observed, as well as a considerable increase in the dye molecule absorption. Possible mechanisms of the phenomena are discussed. [ABSTRACT FROM AUTHOR]

Abstract: The absorption, fluorescence and fluorescence excitation spectra of polymer thin film composites based on poly-N-epoxypropylcarbazole (PEPC) doped with different content of anionic polymethine dye testify to the formation of contact ion-pair associates at high concentration of the latter. The photoconductivity of such composites in the visible spectrum region is observed, despite the absence in the polymer of any fragment capable of accepting a photoexcited electron from anionic dye chromophore. Analysis of the spectral data together with DFT/B3LYP quantum-chemical calculation of the HOMO and LUMO energies of the monomer N-methylcarbazole unit and the radical of the polymethine dye allowed us to suggest the possible mechanism of internal photoeffect in the investigated composites which is based on the formation of the contact ion-pair associates. [Copyright &y& Elsevier]

We have obtained photoconducting film composites based on cobalt(II) oleate and octanoate salts, sensitized by anionic or cationic polymethine dyes. We have studied their electrical conducting and photoconducting properties. High photosensitivity is observed for octanoate-based films, in which the cobalt ion concentration is higher than in oleate-based films. We suggest a scheme for the process of photogeneration of nonequilibrium charge carriers in such composites. [ABSTRACT FROM AUTHOR]

The structural properties of polymethine molecules incorporated into nanofibers of chrysotile asbestos have been studied by absorption-spectroscopy methods. These experiments have shown that, in chrysotile nanotubes, monomeric, all- trans- and cis-isomers, dimers and J aggregates can be observed. Upon incorporation of a dye from weakly concentrated solutions, monomeric forms of polymethine molecules, extended chromophores of which are oriented along parallel asbestos nanotubes, are predominantly observed. The hybrid material under investigation may be of interest for applied problems. [ABSTRACT FROM AUTHOR]

The paper presents a study on modeling the mechanical interaction between the tip of a scanning atomic force microscope (AFM) and surfaces of various types, which makes it possible to optimize parameters and modes for mechanical AFM nanolithography. The practical assessment of mechanical nanoprobe lithography based on the method of a direct surface patterning was carried out during fabrication of functional elements for molecular electronics. Polymethine dye nanowires of a specified configuration and the cross-section 3x20 nm have been successfully formed in a multilayer polytetrafluoroethylene/gold/silicon nanostructure. [ABSTRACT FROM AUTHOR]

Abstract: We identified the conformational structure, aggregation behavior and photophysical properties of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) in various toluene/nonane solutions dependent on nonane content. In dilute solution region (e.g., below the overlap concentration, c*), static light scattering (SLS) revealed that the stiffness of MEH-PPV decreased as nonane content was increased, attributed to a stronger interaction force between MEH-PPV backbones. However, MEH-PPV chains presented a more extended-wormlike conformational structure in toluene. Therefore, a looser intermolecular micellelike aggregates occurred easily between the ether side chains of MEH-PPV at the concentration exceeded the overlapping concentration in toluene and toluene/nonane solutions. Nevertheless, at higher nonane content, the micellelike aggregates were became highly compacted by the π–π complex force between MEH-PPV backbones, dominating the dynamic behaviors and photophysical properties of MEH-PPV in toluene/nonane solution. These results proved that two types of segmental association with distinct stability were identified for the MEH-PPV/toluene/nonane solutions upon prolonged aging. The highly stable, which could not be disrupted by heating, was attributed to the interaction force between ether side chains of MEH-PPV in both solutions. Other type was a weaker affinity force through π–π complex, which could be disrupted thermally, making the micellelike aggregates more compact to form the network structure in MEH-PPV-enriched at higher nonane content. [Copyright &y& Elsevier]

A new 6-dialkylaminobenzimidazole nonlinear optical dye was synthesized in eight linear steps with an overall yield of 16%. [ABSTRACT FROM AUTHOR]

Stimulated by a recent experimental report [Hales JM et al. (2010) Science 327:1485-1488], two-photon absorption and third-order optical nonlinearities of selenopyrylium- and bis(dioxaborine)-terminated polymethine dyes (called SE-7C and DOB-9C) used for all-optical switching were investigated theoretically with time-dependent DFT (TD-DFT) and response theory as well as visualized real-space analysis. The calculated results for the first hyperpolarizability and second hyperpolarizability demonstrated that the two molecules both have large third-order optical nonlinearities. Using real-space analysis, we were able to visually determine that in the one-photon absorption (OPA) process, the first singlet excited state of SE-7C and DOB-9C is an intramolecular charge transfer (ICT) excited state with strong absorption, while the second excited state of these dyes (also termed the 'ICT state') shows weak absorption. However, in the two-photon absorption (TPA) process, a larger TPA absorption cross-section was predicted for the second excited state. In this paper, we describe the properties of the S2 excited state, incorporating charge transfer and the transition moment, via real-space analysis, which was very important for understanding the TPA characteristics of the S state. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: A non-extractive sequential injection spectrophotometric method for the determination of molybdenum has been developed. The method is based on the reaction between the thiocyanate complex of molybdenum and the polymethine dye (2-[2-(4-dipropylamino-phenyl)-vinyl]-1,3,3-trimethyl-3H-indolium chloride) in a hydrochloric acid medium. The calibration plot in the SIA system was linear from 0.080mgL−1 to 1.92mgL−1 of Mo; LOD was 0.021mgL−1. The method was applied for the determination of molybdenum in spiked drinking water and mineral water. [Copyright &y& Elsevier]

The quantum-chemical investigations by ab initio method (restricted Hartree-Fock/6-31G**) have been performed for a series of unsubstituted, monosubstituted, and disubstituted neutral polyenes and their double charged cations. The waves of charge alternation (characterized by the difference in the electron densities at the nearest carbon atoms or Δ q function) and bond length alternation (characterized by the lengths difference of the nearest carbon-carbon bonds or Δ l function) are reported. Comparisons are made with the corresponding monocationic polymethine molecules. We found that ionization by two electrons results in formation of two solitonic waves of charge alternation, rather than superposition of two overlapping solitonic waves into one. These waves behave similar to two independent elastic particles, which do not penetrate into each other despite the special confinement by the length of chromophore π-system. In monosubstituted polyene dication, Δ q and Δ l functions contain two waves each; however, only one wave is mobile and sensitive to a change of the chemical nature of the terminal group, whereas the second wave remains practically unchanged. The introduction of one oxymethyl or phenyl terminal groups leads to a relatively small shift of the mobile wave from the center to a direction of the terminal group. The effect of the amino or tropilium terminal groups is much more pronounced and leads to a shift of the mobile wave to the end of the molecule. In disubstituted polyene dication, both solitonic waves become mobile and shift symmetrically to both ends. The general principles of the charge localization described in this study may be used in molecular design and fine-tuning of the charge transport properties in plastic photovoltaics and other organic semiconducting materials. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Colorless 1,3-bis(dicyanomethylidene)indan is an organic acid (p Ka≈3.0) that turns blue in polar media owing to self-deprotonation. Moreover, its colored conjugate base shows potential as a minimal anionic polymethine dye for probing biomolecules in cells and in vivo through noncovalent complexation and near-infrared fluorescence signaling. [ABSTRACT FROM AUTHOR]

This review gives an overview of the nonlinear transmission (NLT) properties of near-infrared absorbing materials such as naphthalocyanines, extended porphyrins, conjugated polyenes, polymethines and other chromophores. Special attention is given to the mechanism of the NLT effect, discussing the several types mechanisms encountered. It focuses on the most important contributions about materials modulation through organic synthesis versatility, permitting the variation of the different physico-chemical features, and consequently aiming the achievement of effective systems in terms of NLT performance. [ABSTRACT FROM PUBLISHER]

Objective: Intraoperative imaging of intravascular thrombi is limited by the inability of visible light to penetrate thick-walled vessels. Near-infrared (NIR) light has relatively high tissue penetration and low autofluorescence and scatter, offering significant advantages. We hypothesized that the development of 700-nm NIR fluorophores for platelet labeling, in conjunction with existing 800-nm NIR fluorophores, would permit simultaneous and separable quantitation of intravascular thrombi and measurement of the antiplatelet effect of drugs. Methods: We synthesized a series of lipophilic, cationic, polymethine indocyanine dyes (MHI-86, 94, 106, and 114) that emit at approximately 700 nm. Platelet uptake was optimized in vitro and the bioactivity and blood half-life of labeled platelets was characterized in vitro and in vivo. FeCl3-induced injury of the femoral arteries and intravascular thrombus formation was performed in 35-kg Yorkshire pigs. A combination of 700-nm and 800-nm NIR fluorophore-labeled platelets was used in conjunction with the fluorescence-assisted resection and exploration imaging system to image and quantify the antiplatelet effect of cilostazol and acetylsalicylic acid. Results: MHI-114 was incorporated at nearly 4.1 × 106 molecules per platelet without affecting platelet function. When infused into pigs, the signal-to-background ratio of MHI-114-labeled platelets exhibited a blood half-life of 16.4 ± 2.2 (mean ± SEM; n = 3) minute and generated a signal-to-background ratio of 2.5 ± 0.5 (mean ± SEM; n = 3) at the site of thrombi. Using dual-NIR-labeled platelet populations, cilostazol and acetylsalicylic acid were found to cause a reduction in platelet incorporation into thrombi of 51 ± 2% and 10 ± 1% (mean ± SEM; n = 3), respectively, relative to vehicle-only treated control thrombi. Conclusions: New platelet-avid 700-nm NIR fluorophores permit simultaneous two-wavelength NIR fluorescence imaging and quantitation of intravascular thrombi in intact vessels approaching the size of humans and can be used to study the antiplatelet effect of drugs. [Copyright &y& Elsevier]

Aim. To find out approaches for studying cellular functional state using new fluorescent squaraine probes. Methods. Dependence of fluorescence parameters of squaraine and polymethine dyes on the properties of their microenvironment in biomembranes was studied by microspectrofluorimetry. The quantitative microfluorimetry of single cells was applied for the evaluation of probes accumulation in cells and for investigation of dynamics of dyes photobleaching. Results. The data obtained evidence that a chromophoric part of the squaraine dyes molecules is mainly localized in a more polar microenvironment in biomembranes, as compared to the cationic polymethine probes. Conclusions. Chromophore of anionic squaraine probe in native membranes is located in the upper membrane layer in the region of polar phospholipids heads, while the cationic probes can penetrate deeper into the membrane. The anionic squaraine probe SqSC4 was determined as the most photostable dye among the investigated probes. [ABSTRACT FROM AUTHOR]

A quantum-chemical study was carried out on the shape of solitons in ionic polymethine dyes, neutral polyenes, and merocyanines in an electric field. The application of an electric field in neutral conjugated molecules forms a soliton wave of alternating partial charges on atoms, which moves along the field vector. The initially injected charge (electron or hole) is autolocated, while its shape is distorted in the electric field. An increase in the field strength leads to the appearance of two components with minimum charge alternation and maximum bond length alternation between them. A further increase in the field strength leads to bond breaking. The limiting field potentials depend both on the conjugation chain length and nature of the end groups, which act as barriers for the displacement of charge carriers. [ABSTRACT FROM AUTHOR]

Abstract: It is known that polymethine dyes (PD) can form complexes with biomacromolecules, in which, as a rule, fluorescence buildup is observed. In addition, PD possess a unique property to form ordered aggregates of different types (dimers, H- and J-aggregates) both in the free state and on biomacromolecules as templates. This creates a basis for application of PD as spectral-fluorescent probes for biomacromolecules, which is a matter of this review. Besides, the review is devoted to studies of noncovalent interactions of PD with biomacromolecules: nucleic acids, proteins, and some others. [Copyright &y& Elsevier]

Photoluminescence quenching in an external electric field increases and a long-wavelength photoluminescence band and photoconductivity appear in the visible spectrum with increasing concentration of anionic polymethine dye in poly-N-epoxypropylcarbazole films. Associated species containing dye ion pairs are formed with increasing dye concentration. The kinetics found for the growth and relaxation of the photocurrent in these composite films is anomalous for photosemiconductor materials: the time required for growth of the photocurrent is much greater than the time for its relaxation after switching off the light. A prior irradiation memory effect of the films was discovered. [ABSTRACT FROM AUTHOR]

Using the example of layers of symmetric polymethine dyes, we have studied the optical excitation energy transfer processes between nanocomponents of a molecular layer. The fluorescence yields and life-times of excited states of monomeric stereoisomers have been estimated, and the stereoisomerization yields have been determined. We show that the excitation transfer yield between the S states of monomeric stereoisomers (tens of percent) is considerably higher than the fluorescence yield (several percent) and depends on the structure of terminal groups of the molecule. [ABSTRACT FROM AUTHOR]

Novel anionic polymethine dyes were synthesized from 2,7-bis(phenoxysulfonyl)-, 2,7-dinitro-, and 2,4,5,7-tetranitrofluorenes. The reasons for the complicated shape of their absorption spectra were analyzed: the formation of contact ion pairs, associates, and conformational isomers and electronic effects of substituents. The quantum chemical calculations by the Pariser-Parr-Pople method and nonempirical DFT and TDDFT methods in the B3LYP/6-31G(d,p) basis set revealed that the orbitals of the nitro groups, unlike the orbitals of the SOOPh groups, are efficiently conjugated with the common chromophore system inducing additional electron transitions. [ABSTRACT FROM AUTHOR]

In this paper we investigate the effect of terminal substituents on the dynamics of spin and charge transport m donor-acceptor substituted polyenes [D-(CH)X-A] chains, also known as push-pull polyenes. We employ a long-range correlated model Hamiltonian for the D-(CH)X-A system, and time-dependent density matrix renormalization group technique for time propagating the wave packet obtained by injecting a hole at a terminal site, in the ground state of the system. Our studies reveal that the end groups do not affect spin and charge velocities in any significant way, but change the amount of charge transported. We have compared these push-pull systems with donor-acceptor substituted polymethine imine (PMI), D-(CHN)x-A, systems in which besides electron affinities, the nature of pz>.- orbitals in conjugation also alternate from site to site. We note thai spin and charge dynamics in the PMIs are very different from that observed in the case of push-pull polyenes, and within the time scale of our studies, transport of spin and charge leads to the formation of a "quasi-static" state. [ABSTRACT FROM AUTHOR]

Abstract: A novel water-soluble amine-reactive dioxaborine trimethine dye was synthesized in a good yield and characterized. The potential of the dye as a specific reagent for protein labeling was demonstrated with bovine serum albumin and lysozyme. Its interaction with proteins was studied by fluorescence spectroscopy and gel electrophoresis. The covalent binding of this almost nonfluorescent dye to proteins results in a 75- to 78-fold increase of its emission intensity accompanied by a red shift of the fluorescence emission maximum by 27 to 45nm, with fluorescence wavelengths of labeled biomolecules being more than 600nm. The dye does not require activation for the labeling reaction and can be used in a variety of bioassay applications. [Copyright &y& Elsevier]

Abstract: A systematic investigation of the conformational structure was performed for the series of symmetrical and unsymmetrical mono-, tri-, pentamethine cyanines, and styryl dyes bearing 2-azaazulenium terminal group. The rotation energy barriers of terminal groups were determined via the dynamic variable temperature NMR experiments. The conformational transformation energy was calculated by quantum chemical methods (B3LYP and M05-2X) both for the cases of considering the solvent influence and not tacking it into account. Based on the comparison of theoretical and experimental data, relative electron-donating abilities and geometrical features of the heterocyclic terminal groups in 2-azaazulenium dyes were estimated. The arrangement of certain heterocyclic nuclei in order of basicity by considering the results of the dynamic NMR investigations was proposed. Influence of the conjugated chain length and the solvent nature on the conformational lability of the investigated dye molecules was discussed. [Copyright &y& Elsevier]

A collection of smart multicomponent reactions (MCRs) with continuative post condensation cyclizations (PCCs) is presented to construct conventional three- to sevenmembered heterocyclic compounds in diversity oriented syntheses (DOS). These will provide a high degree of applying economical and ecological advantages as well as of practicability. Water, ionic liquids, and solvent-less syntheses as well as use of various forms of energy as microwave and ultrasonic irradiation are examined and discussed. [ABSTRACT FROM AUTHOR]