Dye Aggregation Research Articles

Aggregation of Carbocyanine Dyes in Choline Chloride-Based Deep Eutectic Solvents in the Presence of an Aqueous Base.

Deep eutectic solvents (DESs) have shown potential as novel media to support molecular aggregation. The self-aggregation behavior of two common and popular carbocyanine dyes, 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazole carbocyanine (TDBC) and 5,5'-dichloro-3,3'-di(3-sulfopropyl)-9-methyl-benzothiacarbo cyanine (DMTC), is investigated within DES-based systems under ambient conditions. Although TDBC is known to form J-aggregates in basic aqueous solution, DMTC forms H-aggregates under similar conditions. The DESs used, glyceline and reline, are composed of salt choline chloride and two vastly different H-bond donors, glycerol and urea, respectively, in 1:2 mol ratios. Both DESs in the presence of base are found to support J-aggregates of TDBC. These fluorescent J-aggregates are characterized by small Stokes' shifts and subnanosecond fluorescence lifetimes. Under similar conditions, DMTC forms fluorescent H-aggregates along with J-aggregates within the two DES-based systems. The addition of cationic surfactant cetyltrimethylammonium bromide (CTAB) below its critical micelle concentration (cmc) to a TDBC solution of aqueous base-added glyceline shows the prominent presence of J-aggregates, and increasing the CTAB concentration to above cmc results in the disruption of J-aggregates and the formation of unprecedented H-aggregates. DMTC exclusively forms H-aggregates within a CTAB solution of aqueous base-added glyceline irrespective of the surfactant concentration. Anionic surfactant, sodium dodecylsulfate (SDS), present below its cmc within aqueous base-added DESs supports J-aggregation by TDBC; for similar SDS addition, DMTC forms H-aggregates within the glyceline-based system whereas both H- and J-aggregates exist within the reline-based system. A comparison of the carbocyanine dye behavior in various aqueous base-added DES systems to that in aqueous basic media reveals contrasting aggregation tendencies and/or efficiencies. Surfactants as additives are demonstrated to control and modulate carbocyanine dye self-aggregation within DES-based media. The unique nature of DESs as alternate media toward affecting cyanine dye aggregation is highlighted.

Coherent Exciton Delocalization in a Two-State DNA-Templated Dye Aggregate System.

Coherent exciton delocalization in dye aggregate systems gives rise to a variety of intriguing optical phenomena, including J- and H-aggregate behavior and Davydov splitting. Systems that exhibit coherent exciton delocalization at room temperature are of interest for the development of artificial light-harvesting devices, colorimetric detection schemes, and quantum computers. Here, we report on a simple dye system templated by DNA that exhibits tunable optical properties. At low salt and DNA concentrations, a DNA duplex with two internally functionalized Cy5 dyes (i.e., dimer) persists and displays predominantly J-aggregate behavior. Increasing the salt and/or DNA concentrations was found to promote coupling between two of the DNA duplexes via branch migration, thus forming a four-armed junction (i.e., tetramer) with H-aggregate behavior. This H-tetramer aggregate exhibits a surprisingly large Davydov splitting in its absorbance spectrum that produces a visible color change of the solution from cyan to violet and gives clear evidence of coherent exciton delocalization.

The role of auxiliaries in the immersion dyeing of textile fibres: Part 4 theoretical model to describe the role of liquor ratio in dyeing cellulosic fibres with direct dyes in the absence and presence of inorganic electrolyte

A model is proposed to explain the manner by which the uptake of direct dyes on cellulosic fibres is promoted by a reduction in the liquor ratio used for dyeing. According to the model, which invokes the concept of interstitial water in dyeing, reducing the liquor ratio promotes dye aggregation which reduces the solubility of the dye in the bulk dyebath phase, so that the inherent preference of the dye to favour the aqueous phase shifts towards the fibre phase. It is suggested that the same mechanism accounts for the promotion of direct dye uptake imparted by the addition of inorganic electrolyte to direct dye dyebaths. As such, reduced liquor ratio and added inorganic electrolyte exert a combinatorial promotional effect on direct dye uptake.

Phototransformation of cyanine dye with two chromophores. Effects of oxygen and dye concentration

Abstract Phototransformation of a cyanine dye with two chromophores (biscyanine dye, BCD) subject to visible light in phosphate buffer was studied using optical absorption and fluorescence spectroscopic techniques. The effects of the dye concentration and molecular oxygen were demonstrated. The monoexponencial dependence of optical absorption of the BCD solution on the irradiation time was observed. The increase of the characteristic phototransformation time with the dye concentration is explained in terms of the dye aggregation. The explanation is confirmed by experiments in the presence of SDS micelles, where the concentration effect is absent, since at binding with SDS micelles BCD does not aggregate. The dye phototransformation rate increase in the presence of oxygen is explained in terms of singlet oxygen formation due to energy transfer from the dye excited triplet state to molecular oxygen. Singlet oxygen was detected, and its quantum yield was determined by an indirect chemical method. The effect of singlet oxygen on the BCD phototransformation was confirmed by reduction of its phototransformation rate in the presence of 2,5-dimethylfuran, a known singlet oxygen water soluble quencher. Singlet oxygen may destroy the π-conjugation of the BCD chromophores. A possible structure of the dye photoproduct is proposed based on the similarity of its spectral characteristics and those of monochromophoric cyanine dye and confirmed by quantum chemical modelling.

Structural templating of J-aggregates: Visualizing bis(monoacylglycero)phosphate domains in live cells

Identifying the key structural and dynamical determinants that drive the association of biomolecules, whether in solution, or perhaps more importantly in a membrane environment, has critical implications for our understanding of cellular dynamics, processes, and signaling. With recent advances in high-resolution imaging techniques, from the development of new molecular labels to technical advances in imaging methodologies and platforms, researchers are now reaping the benefits of being able to directly characterize and quantify local dynamics, structures, and conformations in live cells and tissues. These capabilities are providing unique insights into association stoichiometries, interactions, and structures on sub-micron length scales. We previously examined the role of lipid headgroup chemistry and phase state in guiding the formation of pseudoisocyanine (PIC) dye J-aggregates on supported planar bilayers [Langmuir, 25, 10719]. We describe here how these same J-aggregates can report on the in situ formation of organellar membrane domains in live cells. Live cell hyperspectral confocal microscopy using GFP-conjugated GTPase markers of early (Rab5) and late (Rab7) endosomes revealed that the PIC J-aggregates were confined to domains on either the limiting membrane or intralumenal vesicles (ILV) of late endosomes, known to be enriched in the anionic lipid bis(monoacylglycero)phosphate (BMP). Correlated confocal fluorescence - atomic force microscopy performed on endosomal membrane-mimetic supported planar lipid bilayers confirmed BMP-specific templating of the PIC J-aggregates. These data provide strong evidence for the formation of BMP-rich lipid domains during multivesicular body formation and portend the application of structured dye aggregates as markers of cellular membrane domain structure, size, and formation.

A Comparative Study on Two RuII Complexes with Thiophene‐Based Ancillary Ligands for High‐Efficiency Dye‐Sensitized Solar Cells

Heteroleptic polypyridyl Ru complexes MMR‐1 and MMR‐2 containing 2‐(methylthio)thienyl and 2‐(4‐methoxyphenyl)thienyl units on the antennas of ancillary ligands, respectively, were designed, synthesized, and characterized as sensitizers for dye‐sensitized solar cells. The maximum absorption wavelength of MMR‐1 is more red‐shifted than that of MMR‐2, but MMR‐2 has a higher molar extinction coefficient, leading to better light harvesting. Under the same device‐fabrication conditions, the photovoltaic performances of these sensitizers were evaluated while anchored on mesoporous TiO2 and compared to that of the benchmark N719. Both MMR‐1 and MMR‐2 exhibited comparable or even higher solar‐to‐electric conversion efficiencies η with respect to N719 when employed as photosensitizers in DSSCs. Compared to MMR‐1, MMR‐2 exhibited better overall conversion efficiency, which was attributed to the electron‐donating effect of the 4‐methoxyphenyl group and the better absorptivity by harvesting higher‐energy photons. Complex MMR‐2 also showed higher open‐circuit voltage VOC than MMR‐1, which is likely due to the extension of the antenna of the ancillary ligand by inserting a phenyl group, which leads to less dye aggregation. The photovoltaic performance of MMR‐2 was better, with a short‐circuit photocurrent density of 16.76 mA cm–2, a VOC of 0.673 V, a fill factor of 73.5 %, and an η value of 8.29 % with the addition of 0.5 m 4‐tert‐butylpyridine (TBP) compared to 8.18 % for N719.

Three-in-one approach towards efficient organic dye-sensitized solar cells: aggregation suppression, panchromatic absorption and resonance energy transfer.

In the present study, protoporphyrin IX (PPIX) and squarine (SQ2) have been used in a co-sensitized dye-sensitized solar cell (DSSC) to apply their high absorption coefficients in the visible and NIR region of the solar spectrum and to probe the possibility of Förster resonance energy transfer (FRET) between the two dyes. FRET from the donor PPIX to acceptor SQ2 was observed from detailed investigation of the excited-state photophysics of the dye mixture, using time-resolved fluorescence decay measurements. The electron transfer time scales from the dyes to TiO2 have also been characterized for each dye. The current–voltage (I–V) characteristics and the wavelength-dependent photocurrent measurements of the co-sensitized DSSCs reveal that FRET between the two dyes increase the photocurrent as well as the efficiency of the device. From the absorption spectra of the co-sensitized photoanodes, PPIX was observed to be efficiently acting as a co-adsorbent and to reduce the dye aggregation problem of SQ2. It has further been proven by a comparison of the device performance with a chenodeoxycholic acid (CDCA) added to a SQ2-sensitized DSSC. Apart from increasing the absorption window, the FRET-induced enhanced photocurrent and the anti-aggregating behavior of PPIX towards SQ2 are crucial points that improve the performance of the co-sensitized DSSC.

Coherent Random Lasing from Dye Aggregates in Polydimethylsiloxane Thin Films.

The coherent random laser (CRL) from dye-doped polydimethylsiloxane (PDMS) has been investigated in both nanoparticle-doped (NP-doped) thin films and pure dye thin films. Compared with the literature, the pump threshold is only 1.5 mJ/cm2 in the pure dye thin film with a low dye concentration. The spontaneously formed micro-/nanocrystals of Pyrromethene 597 (PM597) dye support both gain and random feedback in the bulk of the PDMS during the sample preparation. When the SiO2 NPs were doped, the pump threshold was reduced to 0.75 mJ/cm2. The threshold increased after the film was peeled off from glass, which indicates that the photon localization effect of the leaky-waveguide structure plays an important role in the reduction of the CRL threshold. By a change in the pump stripe length or the thickness of the film, the peak wavelength red-shifts 6.7 or 5.93 nm, respectively. The PM597 dye molecule solubility changes, and they spontaneously aggregate in the process of toluene volatilization; the PDMS cures, which is the reason for the formation of PM597 micro-/nanocrystals. This thin film random laser with a low dye concentration can be used in integrated optoelectronics and display imaging.

Effects of Chain Parameters on Kinetics of Photochromism in Acrylic-Spiropyran Copolymer Nanoparticles and Their Reversible Optical Data Storage.

Chemical bonding between photochromic compounds and polymer matrices will induce several consitions such as photostability, photoreversibility, elimination of dye aggregation, and undesirable negative photochromism. In such polymeric systems, the switching rate and photoisomerization are closely dependent on several parameters like chain flexibility, steric restrictions, polarity, and even proticity of the surrounding medium. Here, copolymerization of a synthesized spiropyran-based monomer with butyl acrylate (BA) and methyl methacrylate (MMA) comonomers was carried out with various compositions of MMA and BA through emulsion polymerization, and the corresponding photoisomerization kinetics were studied. Particle sizes and their distributions were analyzed by dynamic light scattering, and morphologies were investigated by scanning and transmission electron microscopic analyses. The results showed the particles are spherical with diameter 62-82 nm. Differential scanning calorimetric thermograms were employed to determine Tg of the prepared copolymers, which ranged from -23 to 93 °C. The kinetics of photoisomerization was then studied by UV-vis spectroscopy. Finally, a latex containing spiropyran/acrylic copolymer with Tg of about 0 °C and optimum rate of coloration and decoloration was considered in reversible optical data storage studies due to its fast photochromism and good film-formation properties.

Study of dichlorotriazine reactive dye hydrolysis in siloxane reverse micro-emulsion

The dyeing ability of the dichlorotriazine dye on cotton fiber in siloxane media was investigated using a water/oil emulsion system. Compared with traditional water base dyeing, a deeper color depth of fabric and 90% fixation rate of dye could be achieved without using salts in siloxane reverse micro-emulsion system. The hydrolysis mechanism of dichlorotriazine dye, which deeply affects the dyeing performance, was analyzed using high performance liquid chromatography and mass spectrometric methods. In siloxane reverse micro-emulsion dyeing system, the lower hydrolysis of dye is probably due to the grasping water ability of surfactant, the reaction between fiber and dye, and the dye aggregation under a high concentration of dye. Furthermore, the hydrolysis model shows that the hydrolysis rate constants in traditional water base was about three to four times faster than the one in siloxane reverse micro-emulsion system. The dye hydrolysis mechanism in siloxane reverse micro-emulsion system in this study could successfully guide the siloxane reverse micro-emulsion dyeing technology.

Improved mechanism of polyester dyeing with disperse dyes in finite dyebath

A new sorption mechanism of polyester dyeing with disperse dyes in water is proposed. It is considered dye aggregates could not be sorbed unless they turn into single molecules. However, this theory could not explain numerous sorption phenomena: sorption continues when equilibrium dye concentration exceeds its solubility; dyeing at long liquor ratio, using microencapsulated or crystal‐modified dyes do not change concentration of single dye molecules or dye solubility, but increase sorption rate and quantity in a fixed time. We demonstrate that both single and aggregated dye molecules could be sorbed using CI Disperse Blue 56. Because of the large size and low diffusion rate, dye aggregates could temporarily block sorption channel and prevent entry of other dyes. Therefore, only using extra more dyes could get a dark colour. Series of approaches could be proposed to reduce or eliminate the sorption problems caused by aggregates using the new sorption mechanism.

Twisted donor substituted simple thiophene dyes retard the dye aggregation and charge recombination in dye-sensitized solar cells

Abstract Two novel thiophene 3,4-disubstituted organic dyes with double acceptors at 2,5-position framework photosensitizers were carefully designed and synthesized for the dye sensitized solar cell (DSSC) application. In this submission, the influence of carbazole (Cz) and triphenylaime (NPh3) units substitution at 3,4-position of thiophene is studied. Both the planar structure of carbazole based dyes and three dimension structure of triphenylamine based dyes are found to effectively inhibit the I − /I 3 − and Co +2 /Co +3 electrolyte on TiO 2 surface. The results show that varying the donor position in dyes also effectively works for DSSC application, even if it does not broaden the absorption peak in visible region (for both the dyes) due to the blocking of electron delocalization at 2,5-positions by acceptor units. With two twisted donors at 3,4-position in Cz-Th-Dye, NPh3-Th-Dye the dye aggregation and charge recombination retarded. The optical, electrochemical, density functional theory and TRPL studies were used to estimate the photovoltaic properties of the dyes. The dye having two acceptors on both sides (2,5-position) of thiophene moiety showed efficient electron extraction from the electron donor part. Without using any additives, Cz-Th dye and NPh3-Th dye in presence of cobalt (II/III) redox shuttle, resulted in the power conversion efficiency (η, PCE) of ∼3.4% and 3.1% respectively. By replacing one acceptor with any other donor, these thiophene moiety can effectively work as a new π-spacer in DSSC application.

Investigating coagulation behavior of chitosan with different Al species dual-coagulants in dye wastewater treatment

In this study, chitosan (CS) was used as a coagulant aid with different Al species (Ala/Alb/Alc) to treat disperse yellow (DY) wastewater. The effects of coagulant dosages and initial pH on color removal, floc structure and regrowth were investigated. Results showed that the efficiency could be significantly improved with the addition of CS, due to the strong interaction between flocculants and Al species–dye aggregates. CS with the protonation of amino groups could combine with the azo bond and methyl of DY wastewater. Moreover, larger flocs would be generated as CS was added, especially at lower Al dosages. Based on the experimental results of this research, the initial solution pH had an impact on the hydrolysates of Al species and charge of CS, and further influence the color removal efficiency and floc properties. The color removal efficiency was relatively large at pH 6.0–7.0. The bigger flocs were formed under alkaline condition for Ala and its dual-coagulant, and under acidic condition for Alb/Alc and the corresponding dual-coagulants, respectively. In coagulated water, the values of strength and regrowth also increased as CS was dosed, due to the introduction of bridging and charge neutralization.

Flexible Filter‐Free Narrowband Photodetector with High Gain and Customized Responsive Spectrum

Conventional narrowband photodetection is enabled by coupling broadband photodetectors with complex optical filters. The recently reported charge collection narrowing, an alternative filter‐free strategy, attains very narrowband photodetection at the sacrifice of sensitivity. Herein, a new strategy is proposed to customize the responsive spectrum with high gain by using dye molecules with intrinsically versatile and narrowband absorption. The device configuration is organic dye/Zn0.9Mg0.1O nanoparticles/graphene, where the organic dye serves as the narrowband absorber, graphene serves as the fast carrier transport channel, and Zn0.9Mg0.1O nanoparticles play a triple role of enhancing dye loading, suppressing dye aggregation and blocking charge back recombination. A high responsivity of 8 × 103 A W−1 is thus obtained at a 530 nm response peak with a 60 nm full‐width at half maximum, a four orders of magnitude increase in sensitivity compared to the best narrowband photodetectors reported to date under the comparable electric field. Organic dyes with dual‐band absorption to demonstrate narrowband photodetectors with customized responsive spectrum are further implemented. The approach opens the way to the realization of efficient flexible narrowband photodetection for electronic skin and wearable electronic applications.

Optical properties and photoinduced aggregation of cyanine dyes on silver island films

The optical properties and photoinduced modification of hybrid nanostructures, which are silver island films coated with a layer of cyanine dye, were studied. Experiments were conducted on three dye homologs and films differing in the equivalent thickness of the deposited silver. It was shown that the absorption of a hybrid film is not the sum of the absorption of the molecular layer and the plasmon absorption of the silver. The near fields of nanoparticles (NPs) that form island films increase the absorption of organic molecules, with the greatest increase observed in the band of J-aggregates. The influence of the near fields can be reduced by distancing the molecules from the NPs using an insulating polymer layer. In the presence of silver NPs, the photoinduced modification of the component composition of the layers of the dyes occurs at far lower energy densities. Resonant nanosecond laser pulses lead to the aggregation of molecules in hybrid films.

First-Principles and Molecular Dynamics on A–D(Π)–A Type Sensitizers for Dye-Sensitized Solar Cells: Effects of Various Anchoring Groups on Electronic Coupling and Dye Aggregation

The aggregation effect of five A–D(π)–A organic dyes, 1–5, with different anchoring groups is investigated by a combination of first-principles and molecular dynamics (MD). The dye with CSSH anchoring group (2) exhibits improved optoelectronic properties with the wider absorption range and larger absorption strength as compared with the other four dyes. More importantly, the stacking dimer of 2 has smaller or equal electronic coupling as compared with 1, indicating more efficient electron injection from dye to TiO2. Besides the isolated dyes, the monomer and two H-aggregation configurations of 1 and 2 are adsorbed onto the TiO2 anatase (101) surface to evaluate the injection time and variation of the band gap. The aggregation would be suppressed by choice of the suitable anchoring groups. Even if the aggregation is formed, it is not totally detrimental for the photovoltaic efficiency. The influence of aggregation is complicated and should be evaluated from many aspects.

Nano aggregates of amphiphilic phenanthridine dyes for reversible intermolecular excited state proton transfer

This study presented nano aggregates of new amphiphilic phenanthridine dyes with hydroxy group displaying intensified fluorescence emission of reversible intermolecular excited state proton transfer in mixed organic solvent/H2O solutions.

A contrastive study of adsorption behaviors on polyurethane fiber with diester/diurethane tethered and non-tethered azo disperse dyes

To look for a way to improve the fastness properties of disperse dyes on PU fibers, six diurethane/diester tethered azo disperse dyes were prepared and applied to the dyeing of polyurethane fibers. Their detailed adsorption behaviors including the dyeing rate, build-up properties, surface-adsorbed state of dyes and colorimetric properties were investigated as well as compared with those of non-tethered azo dyes. The results showed that there were great differences in adsorption properties between the two types of dyes. The excellent build-up performance of the non-tethered dyes was caused by the crystal growth on the surface of polyurethane fibers, and the serious aggregation of dyes on the surface of fibers would alter the color shade, decrease the chroma and produce poor colorfastness properties. When the tethered dyes were applied to polyurethane fibers, owing to their larger molecular sizes, a higher temperature (120 °C) was needed to finish the dyeing process within a conventional time of 30–40 min, and the crystal growth on the surface of polyurethane fibers was obviously restricted, so that the color of dyed PU fibers became bright and the colorfastness was notably improved. With additional dye concentration, a medium color depth was obtained. It was further demonstrated that the tethering modification of azo disperse dyes to enhance the colorfastness on polyurethane fibers was feasible.

Plasmonic optical trapping of nanometer-sized J- /H- dye aggregates as explored by fluorescence microspectroscopy.

In the present study, we explored plasmonic optical trapping (POT) of nanometer-sized organic crystals, carbocyanine dye aggregates (JC-1). JC-1 dye forms both J- and H- aggregates in aqueous solution. POT behavior was analyzed using fluorescence microspectroscopy. POT of JC-1 aggregates was realized in an increase in their fluorescence intensity from the focus area upon plasmon excitation. Repeating on-and-off plasmonic excitation resulted in POT of JC-1 aggregates in a trap-and-release mode. Such POT of nanometer-sized dye aggregates lying in a Rayleigh scattering regime (< 100 nm) is important toward molecular manipulation. Furthermore, interestingly, we found that the J-aggregates were preferentially trapped than H-aggregates. It possibly indicates semi-selective optical trapping of nanoparticles on the basis of molecular alignments.

Spectroscopic studies on the interaction between thioglycolic acid (TGA)- capped CdTe quantum dots and cyanine dyes

Three different particle sizes from cadmium telluride semiconductor quantum dots (CdTe QDs)have been prepared using thioglycolic acid as a capping agent in aqueous media. The photophysical behaviorfor these particles has been studied in presence of monomethine dyes belong to thiazole orange (TO) family.The aggregation of the cyanine dyes on QDs surface was attributed to the presence of electrostatic attractionbetween negatively charged thioglycolic capping molecules and the ionic dye. Energy transfer process fromCdTe QDs to cyanine dyes was also studied using electronic absorption and steady state emissionmeasurements. The energy transfer parameters such as Stern- Volmer rate constants Ksv, binding sites n,quenching sphere radius r, critical energy transfer distance R0 and the efficiency of energy transfer E, havebeen calculated. The enhancement in the triplet state emission and absorption for the studied dye in thepresence of QDs was expected to play a role in molecular oxygen sensitization and photodynamic therapy(PDT) as well as photovoltaic applications.