The Experts below are selected from a list of 3795 Experts worldwide ranked by ideXlab platform
Bradley D. Smith - One of the best experts on this subject based on the ideXlab platform.
-
Macrocycle threading using solvatochromic Squaraine dyes
2019Co-Authors: Tia S. Jarvis, Bradley D. SmithAbstract:Non-covalent assembly is an attractive way to fabricate deep-red fluorescent probes for biological imaging. Four new solvatochromic Squaraine dyes with unsymmetric structures are prepared and shown to exhibit macrocyclic encapsulation by tetralactam macrocycle in chloroform solvent or in water. Macrocycle threading in chloroform produces a relatively small 20 nm red-shift in absorption wavelength. In contrast, macrocycle threading in water produces ~80 nm red-shift in absorption wavelength, indicating a large change in polarity surrounding the solvatochromic Squaraine as it transfers from bulk water solution to the relatively non-polar macrocycle interior. The large red-shift in absorption maxima translates into a very large 70-fold enhancement of Squaraine fluorescence. Macrocycle threading in water by two homologous Squaraines was studied and there was a large difference in threading kinetics. Macrocycle threading by a Squaraine with an N-methyl substituent at the end of the structure was 5 million times faster than threading by a Squaraine with an N-propyl substituent.
-
New tetralactam hosts for Squaraine dyes.
Organic & biomolecular chemistry, 2018Co-Authors: Janel M. Dempsey, Qiwei Zhang, Allen G. Oliver, Bradley D. SmithAbstract:The photophysical properties of a deep-red fluorescent Squaraine dye can be improved by encapsulating it within a tetralactam macrocycle. Three new tetralactams are described with different substituents (methyl, methoxy, methylenedioxy) on the macrocycle aromatic sidewalls. The capability of each tetralactam to encapsulate a Squaraine dye in chloroform solution was determined experimentally using absorption, fluorescence, and NMR spectroscopy. Two of the tetralactams were found to thread a Squaraine dye with association constants on the order of 106 M-1, while a third macrocycle exhibited no Squaraine affinity. An X-ray crystal structure of the third tetralactam showed that the substituents sterically blocked Squaraine association. Of the two tetralactams that encapsulate a Squaraine, one induces an increase in Squaraine fluorescence quantum yield, while the other quenches the Squaraine fluorescence. The results suggest that these new Squaraine binding systems will be useful for biological imaging and diagnostics applications.
-
Synthesis and Structure of 3,3-Dimethylindoline Squaraine Rotaxanes.
The Journal of organic chemistry, 2017Co-Authors: Tia S. Jarvis, Carleton G. Collins, Janel M. Dempsey, Allen G. Oliver, Bradley D. SmithAbstract:Squaraine rotaxanes are mechanically interlocked molecules comprised of a dumbbell shaped Squaraine dye inside a tetralactam macrocycle. Previous Squaraine rotaxanes have employed planar Squaraine dyes with 4-aminophenyl, 2-aminothiophene, or N-amino units appended to the central C4O2 core. Here we describe two rotaxanes that encapsulate a 3,3-dimethylindoline Squaraine inside a tetralactam with anthracene sidewalls. The rotaxanes were prepared by a templated clipping reaction and an X-ray crystal structure shows that the Squaraine gem-dimethyl groups force a relatively wide separation between the macrocycle anthracene sidewalls. The decreased interaction between the encapsulated Squaraine and the anthracene sidewalls leads to a smaller red shift of the Squaraine absorption and emission bands. Solution-state studies show that the gem-dimethyl groups in 3,3-dimethylindoline Squaraine dyes are large enough to prevent macrocycle threading or rotaxane unthreading. One of the new rotaxanes emits an orange ligh...
-
Water-soluble, deep-red fluorescent Squaraine rotaxanes.
Organic & biomolecular chemistry, 2011Co-Authors: Erin L. Cole, Easwaran Arunkumar, Shuzhang Xiao, Bryan A. Smith, Bradley D. SmithAbstract:Eight fluorescent Squaraine rotaxanes with deep-red absorption/emission wavelengths were prepared and assessed for chemical stability and suitability as water-soluble, fluorescent tracers. The most stable Squaraine rotaxanes have four large stopper groups attached to the ends of the encapsulated Squaraine, and two members of this structural class have promise as highly fluorescent tracers with rapid renal clearance and very low tissue uptake in living mice.
-
Thermally-activated chemiluminescent Squaraine rotaxane endoperoxide with green emission
Chemical communications (Cambridge England), 2011Co-Authors: Carleton G. Collins, Jeffrey M. Baumes, Bradley D. SmithAbstract:A Squaraine rotaxane endoperoxide with a truncated Squaraine chromophore undergoes a cycloreversion reaction and emits green light that can be transferred to red acceptor dyes. The results demonstrate that chemiluminescence emission for Squaraine rotaxane endoperoxides comes from the excited Squaraine inside the rotaxane.
Kock-yee Law - One of the best experts on this subject based on the ideXlab platform.
-
Synthesis, Characterization, Photophysics, and Photosensitization Studies of Squaraine−Bipyridinium Diads
The Journal of Physical Chemistry B, 1997Co-Authors: Kangning Liang, Kock-yee Law, David G. WhittenAbstract:Two Squaraine−bipyridinium diads designed to study electron transfer between the Squaraine chromophore and the bipyridinium group have been synthesized. The two diads, denoted as C4Sq−By and C12Sq−...
-
Squaraine chemistry: effects of solvent and temperature on the fluorescence emission of Squaraines
Journal of Photochemistry and Photobiology A: Chemistry, 1994Co-Authors: Kock-yee LawAbstract:The Squaraines — a class of donor-acceptor-donor molecules — were shown to exhibit intense multiple fluorescence in the visible region. The three emission bands, designated α, β and γ in the order of decreasing energy, were found to be emissions from the excited state of Squaraine, the excited state of the solute-solvent complex and a relaxed, twisted excited state respectively. In this work, the results of an investigation of the effects of the solvent and temeperature on the absorption and fluorescence emission of bis(4-dibutylaminophenyl)Squaraine (1) are reported. The data confirm that Squaraine forms solute-solvent complexes in solvents. Evidence is provided that the solute-solvent interactions is short range, and that polar solvents usually exert a bathochromic effect on the absorption maximum wavelength λmax. Along with the bathochromic shift, a gradual change in the composition of the emission band, from being dominated by the α emission in ether to being dominated by the β emission in polar solvent, is observed. Both λmax and Keq (the equilibrium constant for complexation) are shown to correlate well with the solvent parameter π*. The results indicate that the solute-solvent complexation process is responsible for the bathromic shift in λmax and the composition change in the emission spectra. This is responsible for the bathochromic shift in λmax and the composition change in the emission spectra. This conclusion is supported by variable and low temperature spectral data. While the lifetime of excited 1 is shown to be independent of the solvent (2.3±0.1 ns), the lifetimes of the excited solute—solvent complex and the relaxed, twisted excited state are solvent sensitive, varying from 0.6 to 3.5 ns respectively. From the fluorescence lifetime and the radiative decay rate, the rate of the radiationless decay, which involves rotation of the CC bond between the phenyl ring and the four-membered ring of Squaraine, can be calculated. The rotation rate is shown to increase rapidly as the twisting of the Squaraine chromophore increases. Finally, this work also shows that the intensity of the γ emission not only by lowering the temperature but also by a rigid matrix at room temperature. The results support the postulation that a twisting motion is required for the generation of the relaxed excited state.
-
Squaraine chemistry. Effect of N-pyrrolidino substitution on the synthesis and solid state properties of Squaraines
Dyes and Pigments, 1993Co-Authors: Kock-yee Law, F. Court BaileyAbstract:Abstract Several symmetrical and unsymmetrical Squaraines bearing N-pyrrolidino groups have been synthesized by condensation of N-pyrrolidinoaniline derivatives with squaric acid or a 1-aryl-2-hydroxycyclobutene-3,4-dione derivative. As compared to Squaraines synthesized from N,N-dimethylanilines, a consistently higher synthetic yield was obtained for the N-pyrrolidino-Squaraines synthesized in the work. The yield improvement is attributable to the high nucteophilicity of N-pyrrolidinoanilines, owing to the rigidized N-pyrrolidino ring structure. N-Pyrrolidino substitution is shown to have very little effect on the physical and spectroscopic properties of Squaraine. Examinations of the solid state properties of N-pyrrolidino substituted Squaraines, by solid state absorption spectroscopy and by X-ray powder diffraction reveal that the N-pyrrolidino group is the only N-alkyl substituent identified thus far that exerts no effect on the aggregation of Squaraine molecules in the microcrystalline state. This implies that N-pyrrolidino Squaraines should be photoconductive and indeed photoconductivities have been observed in xerographic devices incorporating them.
-
A Study of the Photoelectrochemical Effects of Squaraine Aggregate in Monolayer
Journal of The Korean Chemical Society, 1993Co-Authors: Young-soon Kim, Kock-yee Law, David G. WhittenAbstract:Monolayers of pure surfactant Squaraine, DSSQ(4-distearyl amino phenyl-4'-dimethylaminophenylSquaraine), were deposited on electrodes by the Langmuir-Blodgett film technique. The DSSQ film exhibits at ∼530 nm. The absorption is significantly red-shifted from the solution of DSSQ (633 nm in chloroform), suggesting that the Squaraine chromophores form aggregates in the LB film. The photogeneration of the Squaraine aggregates is studied by measuring the photocurrents in photoelectrochemical cells consisting of the Squaraine of the aggregates is found to parallel its absorption spectrum and quantum efficiency as high as 0.3% has been observed. While the photocurrent was attenuated exponentially when stearic acid layers (up to 8 layers) are inserted between the Squaraine layer and the electrode, it is nearly extinguished when the Squaraine layer is over-coated with 2 layers of stearic acid. A model for the observation is proposed and the roles of the electrolytes and oxygen on the photogeneration process will be discussed
-
Squaraine chemistry. Synthesis, characterization, and optical properties of a class of novel unsymmetrical Squaraines: [4-(dimethylamino)phenyl](4'-methoxyphenyl)Squaraine and its derivatives
The Journal of Organic Chemistry, 1992Co-Authors: Kock-yee Law, F. Court BaileyAbstract:A class of novel, unsymmetical Squaraines, namely [4-(dimethylamino)phenyl] (4'-methoxyphenyl)Squaraine and its derivatives USq-1-13, which were designed to improve the spectral response of photoconductive Squaraines in xerographic devices in the visible region, have been synthesized by condensation of 1-aryl-2-hydroxycyclobutene-3,4-diones 3-5 with various N,N-dimethylaniline derivatives. The effects of reaction solvent, temperature, and concentration of drying reagent (tributyl orthoformate) on the yield of Squaraine formation were studied systematically using the synthesis of USq-1 as a model reaction
Luca Beverina - One of the best experts on this subject based on the ideXlab platform.
-
Twists and Turns Around a Square: The Many Faces of Squaraine Chemistry
Synlett, 2014Co-Authors: Luca Beverina, Mauro SassiAbstract:The purpose of this account is to give an overview of the wide variety of available structures that share the common name ‘Squaraines’, with particular attention to the results achieved by our group in the last ten years. The first section of the report is an introduction and a description of the motivation for our interest in Squaraine compounds. The second section includes a survey of the history of Squaraines in the scientific literature, and the third section contains a general description of their synthesis and reactivity, together with reports on our direct experiences of their use in materials science, with a focus on Squaraines in third-generation photovoltaics, nonlinear optics, and photodynamic therapy. In all of the cases, we highlight the establishment of structure–property relationships directed at the design of materials with improved properties. 1 Introduction and Motivation 2 Squaraines in the Scientific Literature 3 Synthesis of Squaraine Compounds 3.1 Symmetric Derivatives 3.2 Nonsymmetric Derivatives 3.3 Bis-Squaraines 3.4 Core-Substituted Squaraines 3.5 Squaraines That We Have Not (Yet) Tried To Make 4 Conclusion
-
Panchromatic Squaraine compounds for broad band light harvesting electronic devices
Journal of Materials Chemistry, 2012Co-Authors: Luca Beverina, Elisabetta Ronchi, Riccardo Ruffo, Matteo M. Salamone, Maddalena Binda, Dario Natali, Marco SampietroAbstract:Squaraine compounds are currently investigated as high performance active components in both organic and hybrid photovoltaic devices as well as in photodetectors. Their most valuable features include a particularly efficient optical absorption in the Vis-NIR region, high polarizability, and a remarkable chemical stability. Their full exploitation is somewhat limited by a negligible absorption in the UV-Vis region (prototypical Squaraines basically do not absorb below 500 nm). The aim of the present paper is the design and synthesis of truly panchromatic Squaraines to be effectively employed as the photoactive materials in Vis operating optoelectronic devices. Our strategy involves the design of Squaraines that are both nonsymmetric and core-substituted with suitable electron-withdrawing groups. We show the effect of such a design strategy by means of UV-Vis spectroscopy, cyclic voltammetry and prototypical device performances rationalization.
-
Regioselective Synthesis of 1,2- vs 1,3-Squaraines
Organic letters, 2011Co-Authors: Elisabetta Ronchi, Luca Beverina, Riccardo Ruffo, Silvia Rizzato, Alberto Albinati, Giorgio A. PaganiAbstract:Squaraines have been known for many decades as very stable and versatile vis–NIR absorbing dyes. They have found applications for example as sensitizers in organic photovoltaics and photodetectors. The most common Squaraine structure is the 1,3-regioisomer. Their 1,2-regioisomers are seldom mentioned and unanimously regarded as side products. A facile direct synthesis of 1,2-Squaraines, highlighting the role played by reaction conditions and electronic factors, is described. The first electrochemical characterization of these dyes is also shown.
-
marked alkyl vs alkenyl substitutent effects on Squaraine dye solid state structure carrier mobility and bulk heterojunction solar cell efficiency
Journal of the American Chemical Society, 2010Co-Authors: Luca Beverina, Giorgio A. Pagani, Tobin J Marks, Fabio Silvestri, Diego Bagnis, Hui Huang, Yan Yao, Henry Yan, Antonio FacchettiAbstract:We report two new Squaraine dyes substituted at the pyrrolic rings with n-hexyl (Squaraine 1) or n-hexenyl (Squaraine 2) chains. Although internal molecular structure variations are minimal, the presence of the terminal double bond results in a much more compact solid-state structure, dramatically affecting charge transport in the thin films; the hole mobility of 2 is ∼5× that of 1, and the BHJ OPV power conversion efficiency (PCE) of 2 is ∼2× that of 1. PCEs surpassing 2% for ambient solution-processed devices are demonstrated, the largest so far achieved for Squaraine-based organic solar cells.
-
Photophysics of Squaraine Dyes: Role of Charge-Transfer in Singlet Oxygen Production and Removal
Journal of Physical Chemistry A, 2010Co-Authors: Patrizio Salice, Brian W. Pedersen, Rasmus Toftegaard, Luca Beverina, Jacob Arnbjerg, Giuliano Andrea Pagani, Peter R OgilbyAbstract:The unique optical properties of Squaraines render these molecules useful for applications that range from xerography to photodynamic therapy. In this regard, Squaraines derived from the condensation of nitrogen-based heterocycles and squaric acid have many promising attributes. Key solution-phase photophysical properties of six such Squaraines have been characterized in this study. One feature of these molecules is a pronounced absorption band in the region ∼600−720 nm that has significant spectral overlap with the fluorescence band (i.e., the Stokes shift is small). As such, effects of emission/reabsorption yield unique excitation wavelength dependent phenomena that are manifested in quantum yields of both fluorescence and sensitized singlet oxygen production. Comparatively small Squaraine-sensitized yields of singlet oxygen production and, independently, large rate constants for Squaraine-induced deactivation of singlet oxygen are consistent with a model in which there is appreciable intra- and intermo...
Leonid D. Patsenker - One of the best experts on this subject based on the ideXlab platform.
-
comparison of a series of hydrophilic Squaraine and cyanine dyes for use as biological labels
Dyes and Pigments, 2013Co-Authors: Larysa Markova, Leonid D. Patsenker, Ewald A TerpetschnigAbstract:Abstract Unlike cyanine dyes, which are widely used as fluorescent probes and labels for biomedical applications Squaraine dyes are less investigated. A series of monoreactive, water-soluble, Squaraine dyes with two aromatic sulfo groups and up to 3 sulfobutyl groups was synthesized and the spectral properties of these dyes were compared to dicarbocyanines of identical structure. Compared to the cyanines in aqueous solutions the Squaraine dyes absorb and emit at shorter wavelengths (630–636 nm/639–645 nm vs. 647–653 nm/665–672 nm), have higher molar absorptivities (284,000–333,000 M−1 cm−1 vs. 242,000–260,000 M−1 cm−1), lower fluorescence quantum yields (4.3–9.4% vs. 27–32%) and lower fluorescence lifetimes (0.2–0.3 ns vs. 1.0–1.2 ns) but the quantum yields and lifetimes substantially increase when bound to proteins (Bovine Serum Albumin (BSA) or antibodies, immunoglobulin G (IgG)). Squaraines with two aromatic sulfo groups show no aggregation tendency up to concentrations of 2 × 10−4 M while the corresponding cyanine dye is free of aggregation up to 5 × 10−4 M. The increase in the number of sulfobutyl groups bears a strong influence on the aggregation tendency of both dye classes upon covalent labeling to BSA and IgG resulting in increased quantum yields and lifetimes of the protein conjugates. Compared to cyanines, Squaraine dyes exhibit higher photostabilities and much higher sensitivity of the quantum yields and fluorescence lifetimes toward the microenvironment and are therefore better suited as fluorescence sensors.
-
Long-Wavelength Probes and Labels Based on Cyanines and Squaraines
Springer Series on Fluorescence, 2010Co-Authors: Leonid D. Patsenker, Anatoliy L. Tatarets, E TerpetschnigAbstract:In this review, we make an attempt to compare the characteristics and applications of red and near infrared cyanine and Squaraine dyes used for biological research, biomedical assays, and high-throughput screening. While the favorable photophysical properties of cyanine dyes makes them predestined as covalent labels, the environmentally sensitive Squaraine dyes are utilizable as both florescent probes and labels. Reducing the aggregation tendencies of these dyes in aqueous media seems to be one of the most promising ways to improve their brightness, fluorescence lifetimes, and photostability. Indolenine-based Squaraines including ring-substituted Squaraines exhibit great potential for the design of bright and sensitive fluorescent probes and labels with increased photostability.
-
synthesis of water soluble ring substituted Squaraine dyes and their evaluation as fluorescent probes and labels
Analytica Chimica Acta, 2006Co-Authors: Anatoliy L. Tatarets, Leonid D. Patsenker, Ewald A Terpetschnig, Irina A Fedyunyayeva, Tatyana S Dyubko, Yevgeniy Povrozin, A O DoroshenkoAbstract:A series of ring-substituted Squaraines absorbing and emitting in the red and NIR spectral region was synthesized and their spectral and photophysical properties (quantum yields, fluorescence lifetimes) and photostabilities were measured and compared to Cy5, a commonly used fluorescent label. The absorption maxima in aqueous media were found to be between 628 and 667 nm and the emission maxima are between 642 and 685 nm. Squaraine dyes exhibit high extinction coefficients (163,000–265,000 M −1 cm −1 ) and lower quantum yields (2–7%) in aqueous buffer but high quantum yields (up to 45%) and long fluorescence lifetimes (up to 3.3 ns) in presence of BSA. Dicyanomethylene- and thio-substituted Squaraines exhibit an additional absorption around 400 nm with extinction coefficients between 21,500 and 44,500 M −1 cm −1 . These dyes are excitable not only with red but also with blue diode lasers or light emitting diodes. Due to the favourable spectral and photophysical properties these dyes can be used as fluorescent probes and labels for intensity- and fluorescence lifetime-based biomedical applications.
-
Synthesis of novel Squaraine dyes and their intermediates
Dyes and Pigments, 2005Co-Authors: Anatoliy L. Tatarets, E Terpetschnig, Irina A. Fedyunyaeva, Leonid D. PatsenkerAbstract:We investigate the reactions of mono-substituted Squaraines with CH-acidic nucleophiles, heterocyclic methylene bases and thionating reagents. The reactions of mono-substituted Squaraines with malononitrile, cyano- and nitroacetic esters, barbituric acid, 1,3-indanedione, NaHS and P4S10 lead to ring-substituted mono-Squaraines. These intermediates are useful for the synthesis of novel Squaraine dyes with interesting photophysical properties. 2004 Elsevier Ltd. All rights reserved.
F. Court Bailey - One of the best experts on this subject based on the ideXlab platform.
-
Squaraine chemistry. Effect of N-pyrrolidino substitution on the synthesis and solid state properties of Squaraines
Dyes and Pigments, 1993Co-Authors: Kock-yee Law, F. Court BaileyAbstract:Abstract Several symmetrical and unsymmetrical Squaraines bearing N-pyrrolidino groups have been synthesized by condensation of N-pyrrolidinoaniline derivatives with squaric acid or a 1-aryl-2-hydroxycyclobutene-3,4-dione derivative. As compared to Squaraines synthesized from N,N-dimethylanilines, a consistently higher synthetic yield was obtained for the N-pyrrolidino-Squaraines synthesized in the work. The yield improvement is attributable to the high nucteophilicity of N-pyrrolidinoanilines, owing to the rigidized N-pyrrolidino ring structure. N-Pyrrolidino substitution is shown to have very little effect on the physical and spectroscopic properties of Squaraine. Examinations of the solid state properties of N-pyrrolidino substituted Squaraines, by solid state absorption spectroscopy and by X-ray powder diffraction reveal that the N-pyrrolidino group is the only N-alkyl substituent identified thus far that exerts no effect on the aggregation of Squaraine molecules in the microcrystalline state. This implies that N-pyrrolidino Squaraines should be photoconductive and indeed photoconductivities have been observed in xerographic devices incorporating them.
-
Squaraine chemistry. Synthesis, characterization, and optical properties of a class of novel unsymmetrical Squaraines: [4-(dimethylamino)phenyl](4'-methoxyphenyl)Squaraine and its derivatives
The Journal of Organic Chemistry, 1992Co-Authors: Kock-yee Law, F. Court BaileyAbstract:A class of novel, unsymmetical Squaraines, namely [4-(dimethylamino)phenyl] (4'-methoxyphenyl)Squaraine and its derivatives USq-1-13, which were designed to improve the spectral response of photoconductive Squaraines in xerographic devices in the visible region, have been synthesized by condensation of 1-aryl-2-hydroxycyclobutene-3,4-diones 3-5 with various N,N-dimethylaniline derivatives. The effects of reaction solvent, temperature, and concentration of drying reagent (tributyl orthoformate) on the yield of Squaraine formation were studied systematically using the synthesis of USq-1 as a model reaction
-
Squaraine chemistry. Synthesis and characterization of Squaraine dyes having self-organizing properties
Dyes and Pigments, 1992Co-Authors: Kock-yee Law, F. Court BaileyAbstract:Abstract A series of mono-substituted N-alkylSquaraines of chain length varying from 2 carbons to 18 carbons have been synthesized by condensing 1-p-dimethylaminophenyl-2-hydroxycyclobutene-3,4-dione with N-methyl-N-alkylanilines. All the N-alkylSquaraines synthesized were soluble in chlorinated solvents and were purified by a solvent extraction technique. Their spectroscopic properties (IR, VIS, 1 H NMR and MS) were found to be typical of Squaraines. Examinations of the solid-state properties of these materials, by solid-state absorption spectroscopy and by X-ray powder diffraction technique, indicate that the molecules of N-alkylSquaraines form microcrystalline aggregates, analogous to those observed in their photoconductive pigmentary analogs, in the solid state. This observation is in contrast to that seen in other soluble Squaraines, where the aggregation is usually perturbed by solubilizing groups. This unique aggregational behavior leads us to propose that there exists a dual intermolecular interaction in the microcrystalline state of N-alkylSquaraines. In addition to the expected intermolecular donor-acceptor interaction between the Squaraine chromophores, a hydrophobic interaction between N-alkyl groups occurs. The N-alkyl groups in these materials not only solubilize the Squaraine but also provide a proper orientation for the aggregation process. This model suggests that N-alkylSquaraines should have the ability to self-organize and form photoconductive aggregates under various processing conditions. This ability has been verified in the case of solution cast thin films by absorption spectroscopy.
