Squarylium Dye Research Articles

Protein labeling with red squarylium dyes for analysis by capillary electrophoresis with laser-induced fluorescence detection

Two new red luminescent asymmetric squarylium dyes (designated "Red-1c and Red-3") have been shown to exhibit absorbance shifts to longer wavelengths upon the addition of protein, along with a concomitant increase in fluorescence emission. Specifically, the absorbance maxima for Red-1c and Red-3 dyes are 607 and 622 nm, respectively, in the absence of HSA, and 642 and 640 nm in the presence of HSA, making the excitation of their protein complexes feasible with inexpensive and robust diode lasers. Fluorescence emission maxima, in the presence of HSA, are 656 and 644 nm for Red-1c and Red-3, respectively. Because of the inherently low fluorescence of the dyes in their free state, Red-1c and Red-3 were used as on-column labels (that is, with the dye incorporated into the separation buffer), thus eliminating the need for sample derivatization prior to injection and separation. A comparison of precolumn and on-column labeling of proteins with these squarylium dyes revealed higher efficiencies and greater sensitivities for on-column labeling, which, when conducted with a basic, high-salt content buffer, permitted baseline resolution of a mixture of five model proteins. LOD for model proteins, such as transferrin, alpha-lactalbumin, BSA, and beta-lactoglobulin A and B, labeled with these dyes and analyzed by CE with LIF detection (CE-LIF) were found to be dependent upon dye concentration and solution pH, and are as low as 5 nM for BSA. Satisfactory linear relationships between peak height (or peak area) and protein concentration were obtained by CE-LIF for this on-column labeling method with Red-3 and Red-1c.

Anisotropy in Third-Order Nonlinear Optical Susceptibility ofa Squarylium Dye in a Nematic Liquid Crystal

A squarylium dye is dissolved in 4-cyano-4′-pentylbiphenyl (5CB)and oriented by sandwiching mixtures between two pieces of rubbed glassplates. The optical absorption spectra of the oriented squaryliumdye-5CB layers exhibit high anisotropy. The third-order nonlinearoptical responses and susceptibilities χ(3)e ofsquarylium dye in 5CB are measured with light polarizations paralleland perpendicular to the orientational direction by the resonantfemtosecond degenerate four-wave mixing (DFWM) technique. Temporalprofiles of the DFWM signal of the oriented squarylium dye-5CB layerswith light polarizations parallel and perpendicular to theorientational direction are measured with a time resolution of 0.3 ps(FWHM), and are found to consist of two components, i.e., the coherentinstantaneous nonlinear response and slow response due to the formationof excited molecules. A high anisotropic ratio of χ(3)e,10.8±1.2, is observed for the oriented layers.

A squaraine-based chemosensor for Hg 2+ and Pb 2+

A novel unsymmetrical cationic squaraine dye ( USqH + ), absorbing in the near-infrared region (600–850 nm), was synthesized by reacting a semi-squaric acid derivative 3-[4-( N, N-dioctylamino)phenyl]-4-hydroxycyclobutene-1,2-dione with the squarylium dye, bis(3-methylbenzothiazol-2-ylidene)squaraine. Addition of micromolar amounts of Hg 2+ and Pb 2+ to solutions of USqH + in dichloromethane brings about significant changes in its absorption spectrum, resulting in a change in colour of the solution from green to pink. The absorption spectrum of the dye is relatively insensitive to other environmentally relevant metal ions, making it possible to visually detect Hg 2+ and Pb 2+ in the presence of other metal ions. Molecular modeling of the complexes at the density functional theory (DFT) and semiempirical PM3 levels strongly suggests that the oxygen atoms are the most likely choice for cation binding. The calculations also indicate a high affinity of Hg 2+ and Pb 2+ toward the formation of 2:1 complexes, which is in good agreement with the experimental results.

Organic bistable memory switching phenomena and H-like aggregates in squarylium dye Langmuir–Blodgett films

We have investigated the relationship between the organic bistable memory switching phenomena and H-like aggregates in squarylium dye Langmuir–Blodgett (SQ LB) films. The current–voltage characteristics of SQ LB films sandwiched between the top gold electrode and the bottom aluminum electrode were measured in a dark vacuum vessel at various temperatures as a function of the number of SQ LB films. Ultraviolet–visible absorption spectra were measured at various temperatures. The switching voltage increased as the temperature increased between room temperature and 100 °C, and did not depend on the number of SQ LB films. The results revealed that conductance switching phenomena were induced at the interface between the top gold electrode and SQ LB films, and caused by the presence of H-like aggregates in the SQ LB films.

Near-Infrared Absorption in Symmetric Squarylium and Croconate Dyes: A Comparative Study Using Symmetry-Adapted Cluster-Configuration Interaction Methods

Symmetric croconate (CR) and squarylium dyes (SQ) are well-known near-infrared (NIR) dyes and, in general, are considered to be donor-acceptor-donor type molecules. It is established in the literature that CR dyes absorb in a longer wavelength region than the corresponding SQ dyes. This has been attributed to the CR ring being a better acceptor than the SQ ring. Thus increasing the donor capacity should lead to a bathochromic shift in both SQ and CR. On the other hand, some experiments reported in the literature have revealed that increasing the conjugation in the donor part of the SQ molecule leads first to red shift, which upon a further increase of the conjugation changes to a blue shift. Hence, to understand the role of the central ring and the substitutions in the absorption of these dyes, we carried out high-level symmetry-adapted cluster-configuration interaction (SAC-CI) calculations of some substituted SQ and CR dyes and compare the absorption energy with the existing experimental data. We found that there is very good agreement. We also carried out SAC-CI calculations of some smaller model molecules, which contain the main oxyallyl substructure. We varied the geometry (angle) of the oxyallyl subgroup and the substitution in these model molecules to establish a correlation with the bathochromic shift. We found that the charge transfer is very small and does not play the key role in the red shift, but on the other hand, the perturbation of the HOMO-LUMO gap (HLG) from both the geometry and substitution seems to be responsible for this shift. We suggest as a design principle that increasing the donor capacity of the groups may not help in the red shift, but introducing groups which perturb the HLG and decrease it without changing the MO character should lead to a larger bathochromic shift.

Large Third-Order Optical Nonlinearity and Fast Response of aSquarylium Dye

The third-order optical nonlinearities and responses of asquarylium dye, 2,4-di-3-guaiazulenyl-1,3-dihydroxycyclobutenediyliumdihydroxide, in tetrahydrofuran (THF) solution and in polystyrene (PS)coating films are measured by the femtosecond degenerate four-wavemixing technique under resonant conditions. The molecularhyperpolarizability γ of the squarylium dye in the THF solution isdetermined to be 3.0×10−29 esu at 764 nm, and itselectronic component γe is determined to be 1.1×10−29 esu. The third-order nonlinear susceptibilityχ(3) of one of the present PS coating films containing thesquarylium dye is as high as 3.1×10−8 esu at 800 nm, andits electronic component χ(3)e is 1.3×10−8 esu.

The Novel Functional Chromophores Based on Squarylium Dyes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electrostatic layer-by-layer self-assembly of anionic squarylium and cationic polyelectrolyte

Alternating thin films of the anionic squarylium (SQ) dye and poly(diallyldimethylammonium chloride) (PDDA) were formed by the sequential deposition of SQ and PDDA from aqueous solution onto a glass substrate. UV–vis absorbance measurements reveal that the bilayer deposition process was linear and highly reproducible from layer to layer.

The Novel Functional Chromophores Based on Squarylium Dyes

Squarylium or squaraine dyes are derived from 1,2-dihydroxycyclobuten-3,4-dione, otherwise known as squaric acids. They are two principal types: the 1,2-bisdonorsubstituted derivatives, and the 1,3-bisdonorsubstituted derivatives. The former are essentially merocyanines and have no distinctive properties, whereas the latter represent a unique type of chromophore, which is neither a merocyanines nor cyanine and has exceptional light absorption characteristics. They also have many functional applications based on their special properties. Thus it was the objective of this research project to synthesize a range of 1,3-squarylium dyes of widely differing structural types, and to investigate their light absorption and fluorescence properties in general, and the color change properties of appropriate examples in particular. Also in this study, the various pHinduced colour change processes were examined.

Role of the Oxyallyl Substructure in the Near Infrared (NIR) Absorption in Symmetrical Dye Derivatives: A Computational Study

It is well-known from experimental studies that the oxyallyl-substructure-based squarylium and croconium dyes absorb in the NIR region of the spectrum. Recently, another dye has been reported (J. Am. Chem. Soc. 2003, 125, 348) which contains the same basic chromophore, but the absorption is red-shifted by at least 300 nm compared to the former dyes and is observed near 1100 nm. To analyze the reasons behind the large red shift, in this work we have carried out symmetry-adapted cluster-configuration interaction (SAC-CI) studies on some of these NIR dyes which contain the oxyallyl substructure. From this study, contrary to the earlier reports, it is seen that the donor groups do not seem to play a major role in the red-shift of the absorption. On the other hand, on the basis of the results of the high-level calculations carried out here and using qualitative molecular orbital theory, it is observed that the orbital interactions play a key role in the red shift. Finally, design principles for the oxyallyl-substructure-based NIR dyes are suggested.

Noncovalent Labeling of Biomolecules with Red and Near- Infrared Dyes

Biopolymers such as proteins and nucleic acids can be labeled with a fluorescent marker to allow for their detection. Covalent labeling is achieved by the reaction of an appropriately functionalized dye marker with a reactive group on a biomolecule. The recent trend, however, is the use of noncovalent labeling that results from strong hydrophobic and/or ionic interactions between the marker and biomolecule of interest. The main advantage of noncovalent labeling is that it affects the functional activity of the biomolecule to a lesser extent. The applications of luminescent cyanine and squarylium dyes are reviewed.

Red Luminescent Squarylium Dyes for Noncovalent HSA Labeling.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Femtosecond timing measurement and control using ultrafast organic thin films

We show a femtosecond timing measurement and control technique using a squarylium dye J-aggregate film, which is an organic thin film that acts as an ultrafast two-dimensional optical switch. Optical pulse timing is directly mapped to space-domain position on the film, and the large area and ultrafast response offer a femtosecond-resolved, large dynamic range, real-time, multichannel timing measurement capability. A timing fluctuation (jitter, wander, and skew) reduction architecture is presented and experimentally demonstrated.

Red Luminescent Squarylium Dyes for Noncovalent HSA Labeling

Abstract Asymmetric squarylium fluorophores with 618–680 nm emissions exhibit significantly enhanced fluorescence and increased quantum yield (maximum 97%) by the formation of 1:1 dye–protein complexes when bound as non-covalent labeling probes to human serum albumin (HSA).

Symmetric and asymmetric squarylium dyes as noncovalent protein labels: a study by fluorimetry and capillary electrophoresis

Noncovalent interactions between two squarylium dyes and various model proteins have been explored. NN127 and SQ-3 are symmetric and asymmetric squarylium dyes, respectively, the fluorescence emissions of which have been shown to be enhanced upon complexation with proteins such as bovine serum albumin (BSA), human serum albumin (HSA), β-lactoglobulin A, and trypsinogen. Although these dyes are poorly soluble in aqueous solution, they can be dissolved first in methanol followed by dilution with aqueous buffer without precipitation, and are then suitable for use as fluorescent labels in protein determination studies. The nature of interactions between these dyes and proteins was studied using a variety of buffer systems, and it was found that electrostatic interactions are involved but not dominant. Dye/protein stoichiometries in the noncovalent complexes were found to be 1:1 for SQ-3, although various possible stoichiometries were found for NN127 depending upon pH and protein. Association constants on the order of 10 5 and 10 7 were found for noncovalent complexes of SQ-3 and NN127, respectively, with HSA, indicating stronger interactions of the symmetric dye with proteins. Finally, HSA complexes with NN127 were determined by capillary electrophoresis with laser-induced fluorescence detection (CE–LIF). In particular, NN127 shows promise as a reagent capable of fluorescently labeling analyte proteins for analysis by CE–LIF without itself being significantly fluorescent under the aqueous solution conditions studied herein.

Properties of unsymmetrical squarylium dyes containing strongly electron-donating 4′-amino-2,2′-bis(diethylamino)-4,5′-bithiazole residue

Novel unsymmetrical squarylium dyes containing the strongly electron-donating 4′-amino-2,2′-bis(diethylamino)-4,5′-bithiazole moiety were fluorescent and showed emission maxima around 640 nm. They have both alternant and intramolecular charge-transfer chromophoric systems.

スクアリリウム色素を導入した高分子液晶の合成

二色性スクアリリウム色素を導入した新規な高分子液晶を合成するために, はじめに, スクアリリウム色素の二色性特性について検討し, ベンゾチアゾール系非対称型スクアリリウム色素に良好な二色性特性を見いだした。良好な二色性を示しかつ重合性基を有するスクアリリウ色素として, はじめにN-ヒドロキシル基を有するベンゾチアゾール系非対称型スクアリリウム色素を合成し, さらにアクリロイル基を有する安息香酸誘導体とヨウ化2-クロロ-1-メチルピリジニウム, DMAP存在下, ベンゼン中, 65℃, 12時間反応させて, アクリル酸エステル部位を有するベンゾチアゾール系非対称型スクアリリウム色素3を収率17%-22%で得た。このようなスクアリリウム色素を含むアクリル酸エステルモノマー3とメソゲンモノマーである (6-アクリロイルオキシヘキシロキシ) 安息香酸 (4-シアノ) フェニルと70℃, 24時間ラジカル共重合させて1.0%または0.75%のスクアリリウム色素を含む新規な高分子液晶を得た。

Femtosecond optical switches by squarylium dye J-aggregates films

Formation of Langmuir and spincoated films containing squarylium dye (SQ) J-aggregates and their femtosecond optical response are described. Pump–probe measurements show that saturable absorption of SQJ-films reveal ultrafast decay with time constants of 100–300 fs. We have applied SQJ-film to new femtosecond time-to-space conversion. A pump (gate) pulse and a train of four probe (signal) pulses were illuminated on the same area of the film in the direction of oblique and normal to the film-plane respectively. Demultiplexing operation for T bps optical signals was demonstrated with femtosecond nonlinear optical response of the SQJ-film.

Microstructure of squarylium dye J aggregate films examined on the basis of optical behavior at low temperature

The microstructure of a spin-coated film of squarylium dye J aggregates is examined on the basis of the measurement of the optical properties and the third-order nonlinear optical susceptibility χ(3) at low temperature. The absorption maximum of J aggregates shifted to lower energies as the film temperature decreased, while χ(3) was independent of the temperature. The latter finding indicates that the coherent length of J aggregates is confined by a structural boundary rather than by phonons; consequently, the observed peak energy shift can be due to temperature-dependent conformational change of the aggregates. The small aggregation size may contribute to the ultrahigh-speed optical response of squarylium dye J aggregates.

Absorption spectra, aggregation and photofading behaviour of near-infrared absorbing squarylium dyes containing perimidine moiety

Representatives of a new class of squarylium dyes containing a perimidine moiety have been synthesized and characterized. Almost all of these dyes absorbed near infrared light over 800 nm. The light absorption characteristics of these dyes are well accounted for with the PPP-MO calculation. The photostability properties of the dyes were also investigated when hydroperinidine containing quinoline moiety was introduced, the photochemical stability being better than that of dihydroperimidine moiety. The aggregation of the dyes were also studied in different DMSO/water solution.