Squarylium Cyanine Research Articles

Towards amorphous solution-processed small-molecule photovoltaic cells by design

Abstract Organic photovoltaic cells incorporating a homogeneously blended amorphous active layer were fabricated using a novel glass-forming squarylium cyanine derivative (SQ-glass) as donor, and both a previously reported glass-forming diketopyrrolopyrrole (DPP-glass) and the benchmark PC 61 BM as acceptors. Whereas devices with DPP-glass always yielded an amorphous active layer, devices with PCBM could be either fully amorphous, or phase-segregated with crystalline PCBM, depending on processing conditions. Amorphous devices yielded efficiencies ranging up to 0.41–0.44%, while the efficiency of devices with crystalline PCBM reached up to 0.56%, which corresponds to only a 18% increase relative to a fully amorphous active layer. Although phase-segregated active layers are known to show a higher efficiency, this difference is smaller than anticipated, and is mitigated by the absence in amorphous films of various defects common in their polycrystalline counterparts.

Determination of Morphine and Its Metabolites in Human Urine by Capillary Electrophoresis with Laser Induced Fluorescence Detection Employing On-Column Labeling with a New Boronic Acid Functionalized Squarylium Cyanine Dye

A novel method for the labeling and rapid separation of morphine, morphine-3-beta-d-glucuronide (M3G) and morphine-6-beta-d-glucuronide (M6G) in human urine employing a new boronic acid functionalized squarylium dye (SQ-BA3) and capillary electrophoresis with laser induced fluorescence detection (CE-LIF) is described. The spectrochemical properties, solution stability, pH range, and mechanisms for interactions with morphine and its metabolites were first established for SQ-BA3, followed by optimization of an on-column labeling procedure and CE-LIF method. SQ-BA3 itself was shown to be unstable and weakly fluorescent in aqueous buffers due to aggregate formation. However, SQ-BA3 showed a relative stability and dramatic increase in fluorescence intensity upon the addition of morphine, M3G, and M6G. Because of the low background fluorescence of this dye, on-column labeling was feasible, leading to a simple and rapid analytical method with the potential for clinical applications.

Tunable Self‐Assembled Micro/Nanostructures of Carboxyl‐Functionalized Squarylium Cyanine for Ammonia Sensing

Orderly molecular self‐assembly for tunable micro/nanostructures is an effective way to prepare novel functional materials with desired properties. Squarylium cyanine (SCy) dyes have received great attention in the fields of laser, imaging, and optoelectronic device. However, the detailed self‐assembly behavior of SCy has rarely been investigated. In the present work, two SCy derivatives, D1 and D2, respectively, bearing four and two carboxylic acid groups at different positions are prepared and used as a model system to investigate the molecular self‐assembly, morphology, and optical properties of SCy dyes. The hydrogen‐bonding interactions between the carboxylic acid groups in D1 and D2 are determined with X‐ray diffraction, 2D nuclear magnetic resonance, and Fourier transformation infrared spectroscopy. The two types of hydrogen bonds in D1 cooperating with inherent π–π stacking interaction result in tunable molecular aggregations, which further leads to the transformation between J‐aggregation and H‐aggregation of D1 in the solid state in response to ammonia gas. In all, this work provides a feasible and effective way to study the self‐assembled aggregates of SCy dyes at both molecular and supramolecular levels, and has developed a reversible sensor for ammonia gas detection.

Molecular design of boronic acid-functionalized squarylium cyanine dyes for multiple discriminant analysis of sialic acid in biological samples: selectivity toward monosaccharides controlled by different alkyl side chain lengths.

We designed a new series of boronic acid-functionalized squarylium cyanine dyes (SQ-BA) with different lengths of alkyl chain residues, suitable for multiple discriminant analysis (MDA) of sialic acid (Neu5Ac) in biological samples. The SQ-BA dyes form aggregates based on hydrophobic interactions, which result in quenched fluorescence in aqueous solutions. When the boronic acid binds with saccharides, the fluorescence intensity increases as a result of dissociation to the emissive monomeric complex. We inferred that different dye aggregate structures (H-aggregates and J-aggregates) were induced depending on the alkyl chain length, so that monosaccharides would be recognized in different ways (especially, multipoint interaction with J-aggregates). A distinctive emission enhancement of SQ-BA dyes with shorter-alkyl-chains in the presence of Neu5Ac was observed (2.4-fold fluorescence enhancement; with formation constant 10(1.7) M(-1)), with no such enhancement for SQ-BA dyes with longer-alkyl-chain. In addition, various enhancement factors for other monosaccharides were observed depending on the alkyl chain length. Detailed thermodynamic and NMR studies of the SQ-BA complexes revealed the unique recognition mechanism: the dye aggregate with a shorter-alkyl-chain causes the slipped parallel structure and forms a stable 2:1 complex with Neu5Ac, as distinct from longer-alkyl-chain dyes, which form a 1:1 monomeric complex. MDA using the four SQ-BA dyes was performed for human urine samples, resulting in the successful discrimination between normal and abnormal Neu5Ac levels characteristic of disease. Thus, we successfully controlled various responses to similar monosaccharides with a novel approach that chemically modified not the boronic acid moiety itself but the length of the alkyl chain residue attached to the dye in order to generate specificity.

Photo-Degradation Alkali Lignin by Bis-(2-Methyl Quinoline) Squarylium Cyanine TiO2 Photocatalyst in Sunlight

Photo-degradation alkali lignin was prepared in sunlight by the system of TiO2 and squaraine dye (QSC). The influence of the ratio of QSC to TiO2 on the solar energy conversion efficiency was tested; the principle of degradation alkali lignin by TiO2 photocatalyst in sunlight was researched. The results showed that the number-average and mass-average molecular mass of degradation alkali lignin and the control lignin were 1,548 and 2,822, respectively, the phenolic hydroxyl of degradation alkali lignin is 5.63% with the control is 4.64%, and alcoholic hydroxyl of degradation alkali lignin is 3.21% with the control is 3.77%.

Photochemical properties of squarylium cyanine dyes

This study presents several new squarylium dyes derived from benzothiazole and benzoselenazole with several structural variations, namely the nature of the heteroaromatic ring and the length of the N,N'-dialkyl groups. Before being investigated in connection with their effect on living cells and/or tissues, these novel compounds were characterized, namely with respect to the determination of their main photophysical parameters. Therefore, a study of the ground state absorption, fluorescence emission (quantum yields and lifetimes) and singlet oxygen generation quantum yields was performed for all the compounds synthesized in order to evaluate their efficiency as photosensitizers. An increase of the alkyl chain length from ethyl to hexyl did not produce a clear change in the fluorescence quantum yields, showing no influence on the photoisomerization process. Heavy atom inclusion (Se instead of S) enhanced the singlet oxygen generation efficiency and decreased the intensity of the fluorescence emission. The external heavy atom effect (I(-) as a counterion instead of CF3SO3(-)) produced a significant increase in the singlet oxygen formation quantum yield (about 20%). Transient absorption studies in aerated and oxygen free samples revealed that the photoisomerization process, which could compete with the triplet state formation for all dyes in solution, is a negligible pathway for the excited state deactivation, in accordance with the rigidity introduced by the squaric ring into the polymethine chain of the dye, both in chloroform and ethanol. However, in the case of the chloroform solution a new transient was detected in air equilibrated solutions, resulting from a reaction of the excited squarylium dye in the singlet state with CHCl3˙, and assigned to the radical cation (SQ(+)˙) of the dye.

Basics, Mechanisms and Properties in the Chemistry of Cyanine Dyes: A Review Paper

Some essential basics, mechanisms and properties in the chemistry of cyanine dyes are reviewed, explained and/or illustrated in the paper. This involves and/or covers the generic structure of cyanine dyes, mesomeric structures of cyanine dyes, charge of the dye unit, quaternary salts used in the preparation of cyanine dyes, mechanism of styryl cyanine dyes, mechanism of aza-styryl cyanine dyes, mechanism of acyclic merocyanine dyes, mechanism of cyclic merocyanine dyes, mechanism of aromatic squarylium cyanine dyes, mechanism of heterocyclic squarylium cyanine dyes, acid-base properties of cyanine dyes, determination of the pKa values of cyanine dyes, solvatochromism, general and specific solvent effects, mixed solvent effects, advantages of cyanine dyes and disadvantages of cyanine dyes. In addition, in the introduction section of this review article some light is shed on the uses and applications of cyanine dyes. Keywords: Cyanine dyes, basics in cyanine dyes, mechanisms of cyanine dyes, properties of cyanine dyes.

A long-wavelength fluorescent squarylium cyanine dye possessing boronic acid for sensing monosaccharides and glycoproteins with high enhancement in aqueous solution.

Fluorescence sensing of saccharides and glycoproteins using a boronic acid functionalized squarylium cyanine dye (“SQ-BA”) is characterized in terms of synthetic, fluorometric, thermodynamic and kinetic parameters. In our previous work, this newly synthesized dye was successfully applied to the separation and quantification of Gram-positive bacteria by capillary electrophoresis with laser-induced fluorescence detection (CE-LIF); however, the fundamental properties of the dye and its saccharide complexes still required elucidation, as presented in this paper. The dye itself forms nonemissive, soluble aggregates in aqueous solution. With the addition of a monosaccharide, the dye aggregate dissociates to form an emissive monomer accompanied by the formation of a cyclic cis-diol ester with long-wavelength emission (λex = 630 nm, λem = 660 nm). A very large fluorescence enhancement factor of 18× was observed for the sensing dye as a fructose complex at pH 10, yielding a limit of detection of 10 μM fructose. The relative order of fluorescence enhancement of SQ-BA with other monosaccharides was found to be: fructose > ribose > arabinose ≈ galactose > xylose > mannose > rhamnose > fucose ≈ glucose; and apparent affinity constants of 102.80, 102.08 and 100.86 M−1 were determined for fructose, ribose and glucose, respectively. Formation of the emissive complexes occurred within minutes, proving the kinetics of the sugar-dye interactions to be suitable for on-column labeling methods in CE-LIF. Furthermore, the sensing dye was successfully applied to glycoproteins, mucin type I–S and type III, which were detected with high sensitivity in batch aqueous solution as a result of the sugar-selective boronic acid-diol esterification as well as hydrophobic interactions.

On-Column Labeling of Gram-Positive Bacteria with a Boronic Acid Functionalized Squarylium Cyanine Dye for Analysis by Polymer-Enhanced Capillary Transient Isotachophoresis

A new asymmetric, squarylium cyanine dye functionalized by boronic acid ("SQ-BA") was designed and synthesized for on-capillary labeling of gram-positive bacteria to provide for high sensitivity detection by way of a modified form of capillary electrophoresis with laser induced fluorescence detection (CE-LIF). The CE-based separation employed a polymer-enhanced buffer with capillary transient isotachophoresis in a new hybrid method dubbed "PectI." It was found that the addition of various monosaccharides to SQ-BA in a batch aqueous solution greatly enhanced the emission of the boronic acid functionalized dye by a factor of up to 18.3 at a long wavelength (λ(ex) = 630 nm, λ(em) = 660 nm) with a high affinity constant (K = ~10(2.80) M(-1)) superior to other sugar probes. Semiempirical quantum mechanics calculations suggest that the mechanism for this high enhancement may involve the dissociation of initially nonemissive dye associates (stabilized by an intramolecular hydrogen bond) upon complex formation with sugars. The fluorescence emission of SQ-BA was also significantly enhanced in the presence of a gram-positive bacterial spore, Bacillus globigii (Bg), which serves as a simulant of B. anthracis (or anthrax) and which possesses a peptidoglycan (sugar)-rich spore coat to provide ample sites for interaction with the dye. Several peaks were observed for a pure Bg sample even with polyethyleneoxide (PEO) present in the CE separation buffer, despite the polymer's previously demonstrated ability to focus microoorganisms to a single peak during migration. Likewise, several peaks were observed for a Bg sample when capillary transient isotachophoresis (ctITP) alone was employed. However, the new combination of these techniques as "PectI" dramatically and reproducibly focused the bacteria to a single peak with no staining procedure. Using PectI, the trace detection of Bg spores (corresponding to approximately three cells per injection) along with separation efficiency enough to separate Bg from another gram-positive bacteria, Saccharomyces cerevisiae (resolution, R(s) = 6.09, and apparent plate number, N = 2.7-3.3 × 10(5)), were successfully achieved.

Crystal structures of a benzoselenazole-derived squarylium cyanine dye and three derivatives substituted at the central squaric ring

The crystal structures of 4-[(3-hexylbenzoselenazol-3-ium-2-yl)methylidene]-2-[(3-hexyl-3H-benzoselenazol-2-ylidene)methyl]-3-oxocyclobut-1-en-1-olate and its analogues substituted at the squaric ring with O-methyl, NH-methyl and N,N-diethylamino groups have been determined using single crystal X-ray crystallography techniques. The unsubstituted squaraine dye is symmetrical and packs as a stepped ribbon array (via a C–H⋯O close interaction), which is in contrast to the slip-stacked arrangements observed in similar squaraine analogues. Each of the substituted analogues is asymmetric and pack in slightly differing slip-stacked charge-transfer columns. The NH-methyl analogue packs with a single water molecule per squaraine unit.

Enhanced Photocatalytic Activity for Titanium Dioxide in Sunlight by a Kind of Squarylium Cyanine Dye

The research synthesized bis-(2-methyl quinoline) squarylium cyanine (abbr. QYCD). It was used as dye to enhance the photocatalytic activity of nano-TiO2 in sunlight. Then the photocatalytic process of removal of benzene was investigated indoor air. Results reveal that bis-(2-methyl quinoline)- squarylium cyanine has an intense absorption in the light region of 200nm - 800 nm. The Benzene removal of QYCD-nano-TiO2 complex catalyst at 78h was 97.69%, at the same time it was 36.96% higher as compared with that of nano-TiO2.

The synthesis and characterization of novel, aza-substituted squarylium cyanine dyes

Several squarylium cyanine dyes derived from benzothiazole, benzoselenazole and quinoline were synthesised and the central four member ring functionalized by substitution of one of the oxygen atoms by benzylamine, aniline, 3-iodoaniline, N, N-dimethylhydrazine and 2-aminosulfonic acid groups. All of the ensuing, novel aza-substituted dyes displayed strong absorption within the range 651–709 nm.

Mechanism of squarylium cyanine and Ru(dcbpy) 2(NCS) 2 co-sensitization of colloidal TiO 2

We have investigated the mechanism of squarylium cyanine (SQC) and Ru(dcbpy) 2(NCS) 2 (N3) co-sensitization of colloidal TiO 2 by means of time-resolved spectroscopies. Picosecond time-resolved fluorescence measurements combined with solvent–effect tests revealed a planar and a twisted conformer of the lowest singlet-excited state SQC ( 1SQC*). Quenching of 1SQC* fluorescence by adsorption on TiO 2 and further by co-adsorption with N3 was observed, which are ascribed to the 1SQC*-to-TiO 2 and 1SQC*-to-N3 + electron transfer (ET) reactions based on femtosecond time-resolved absorption results. The planar and the twisted 1SQC* conformers are able to inject electrons into the conduction band of TiO 2 with the rates of 1/2.76 ns −1 and 1/0.30 ns −1, and to reduce N3 + with the rates of 1/2.56 ns −1 and 1/0.28 ns −1, respectively. The latter pair of rates are significantly larger than those of the TiO 2(e −)-to-N3 + back electron transfer (BET) reactions. In addition, ground state SQC is also found to be able to efficiently reduce N3 + with a rate constant of 1/0.32 ns −1. These results imply that minor amount of SQC as a co-adsorbate can effectively intercept the TiO 2(e −)-to-N3 + BET, a mechanism which accounts for the improvement of light-to-electricity conversion efficiency of dye-sensitized solar cells through N3 and SQC co-sensitization (D. Zhang et al., J. Photochem. Photobiol. A: Chem. 135 (2000) 235).

Synthesis and Photochemical Evaluation of Iodinated Squarylium Cyanine Dyes

AbstractSeveral (multiply) iodinated squarylium cyanine dyes of type 1 and 8 (see Scheme and Table), derived from 1,3‐benzothiazole and 6‐iodo‐1,3‐benzothiazole, were synthesized as potential new photosensitizers, with absorptions in the 700‐nm region. Their ability to generate singlet oxygen (1O2) was assessed by luminescence‐decay measurement in the near‐IR. Some of these new dyes show interesting photophysical properties, and may be potentially used in photodynamic therapy (PDT).

Electronic structure and photochemistry of squaraine dyes: basic theoretical analysis and direct detection of the photoisomer of a symmetrical squarylium cyanine.

The photoisomerization kinetics of a squaraine dye has been the object both of experimental investigation and of interpretation in the framework of a qualitative theoretical model formulated by the aid of simple HMO calculations and orbital symmetry considerations. Such a model has first confirmed that the electronic structure and the spectroscopic properties of symmetrical squaraines are related to those of the parent cyanines, with ketocyanines as intermediate systems. Extension of the approach to structures twisted by 90[degree] about a polymethine bond has then provided insight into the electronic aspects and the mechanism of the photoisomerization of the squaraine under study. The reaction, previously indirectly investigated by fluorescence analysis, has been directly monitored by laser flash photolysis. These experiments indicate that, while photoisomerization is likely the main radiationless decay route from the spectroscopic minimum of the lowest excited singlet state (S(1)), the cis photoisomer is produced with only a 1% yield, likely because of an unfavourable cis/trans branching ratio from the perpendicular minimum of the S(1)-state potential energy surface. In contrast with what found for symmetrical cyanines, an increase in the solvent polarity was found to accelerate both the direct, excited-state reaction and, to a much larger extent, the ground-state back-isomerization. Such observations are consistent with predictions of the theoretical model and provide a clue for the identification of the isomerization coordinate.

Efficient sensitization of nanocrystalline TiO2 films with cyanine and merocyanine organic dyes

Abstract Various kinds of cyanine and merocyanine organic dyes having short anchoring groups as sensitizers on nanocrystalline TiO2 electrodes were investigated to promote the short-circuit photocurrent (Jsc) and the solar light-to-power conversion efficiency (ηsun). The Jsc and ηsun improved when the three different three dyes (yellow and red cyanine dyes, and blue squarylium cyanine dye) were adsorbed simultaneously on a TiO2 electrode, as compared with the Jsc and ηsun of the TiO2 electrodes adsorbed by each single dye. The maximum ηsun was 3.1% (AM-1.5, 100 mW/cm2). The Jsc and ηsun were influenced by the solvents for the dye adsorption on the TiO2 electrode, and the efficiencies were improved by the addition of some cholic acids into the dye solution for adsorption. The electron transfer and/or the energy transfer from the red cyanine dye to the blue cyanine dye was observed on a SiO2 film using emission spectroscopy, suggesting a strong interaction between two dyes. The J-like aggregates of the blue cyanine dyes hardly showed sensitization efficiency.

Singlet oxygen generation ability of squarylium cyanine dyes

The quantum yields for singlet oxygen generation of several squarylium cyanine dyes derived from benzothiazole, benzoselenazole and quinoline, displaying absorption within the so-called “phototherapeutic window” (600–1000 nm), were determined, envisioning their potential usefulness for photodynamic therapy (PDT). The determination was performed by a direct method measuring the luminescence decay of the dyes in the near infrared. Considering the absorption and the quantum yields displayed by some of the dyes, these seemed to be potential candidates as sensitizers for PDT.

Synthesis of cyanine dyes derived from benzotellurazo-15-crown-5

A series of crown ether cyanine dyes including crown ether styryl cyanine dyes, crown ether merocyanine dyes and crown ether squarylium cyanine dyes (unsymmetric and symmetric) derived from key intermediate 2-methyl-5,6(15-crown-5)benzotellurazole (1) were prepared.

Photosensitization of nanocrystalline TiO 2 electrodes by squarylium cyanine incorporated with a ruthenium bipyridyl complex

Photosensitization of nanocrystalline TiO 2 electrodes by adsorbing squarylium cyanine (SQ) and a mixture of squarylium cyanine and ruthenium bipyridyl complex (RuL 2(NCS) 2) has been investigated. Photocurrent generation from the monomers and H-type aggregates of squarylium cyanine were observed in the action spectra of squarylium cyanine sensitized electrodes. Adsorption of mixtures of squarylium cyanine and ruthenium bipyridyl complex on nanocrystalline TiO 2 electrodes was studied by absorption and infrared spectra. An association effect of photosensitization was observed in mixtures with molar proportions (SQ:RuL 2(NCS) 2) of 1:20, 1:50 and 1:100 mol/mol, resulting in the increase of the photoelectric response. Electron transfer mechanism was suggested in terms of quenching the fluorescence of squarylium cyanine by the presence of ruthenium bipyridyl complex and TiO 2 colloids.

Mechanistic study of the TiO2-assisted photodegradation of squarylium cyanine dye in methanolic suspensions exposed to visible light

Details of the degradation pathway(s) of squarylium cyanine (SQ) dye in methanolic TiO2 dispersions under visible light irradiation were probed in an attempt to more clearly understand the photodegradation mechanism of dye under visible radiation. For SQ, degradation begins by cleavage of the CC double bond to yield ultimately the final product 1-sulfopropyl-3,3-dimethyl-5-bromoindolenium-2-one. A considerable amount of H2O2 is also formed during degradation through reduction (but not through dismutation) of the superoxide radical anion. In comparison with the previous results in aqueous media, it is evidenced for the first time that the pathway for the TiO2-assisted photodegradation of SQ using visible light irradiation is initiated by a series of complex reactions involving the dye cation radical SQ•+ with dissolved dioxygen and does not implicate any of the photogenerated active oxygen species such as •OH, O2•− and •OOH radicals. These results clarify the previous equivocal conceptions on the details of the reaction between dye cationic radical and oxygen species.