Dye Aggregation Research Articles

Interfacial properties of high-order aggregation of organic dyes: A combination of static and dynamic properties

Aggregation is inevitable for the organic dyes, and it is difficult to evaluate its effects due to its complexity. Herein, we combine first principles and molecular dynamics (MD) simulations to explore the influence of aggregation on the optical and electronic properties for THI-BTZ-2T-C. If only the static properties are considered, the configuration of dye is not varied greatly when the adsorbed dyes are increased from monomer to hexamer. However, the absorption spectrum varies regularly with the increased aggregation order. In addition, the contribution of different orbitals of various atoms to density of states (DOS) gradually increases with the aggregation order increasing. When dynamics simulation is performed, the torsion between different components of dye is enlarged. Meanwhile, the perpendicular model is altered during the dynamics simulations, the dye would like to bend towards the TiO2 surface. Moreover, the electronic coupling is greatly improved during the molecular dynamics simulations especially for the H-aggregation. The dye aggregation mainly affects the electrons injection process resulting in the reduction of the photoelectric conversion efficiency for dye sensitized solar cells (DSSCs). Reduction of perfect face to face stacking would be an efficient pathway to weaken the aggregation.

Merocyanine-540 grafted on ZnS and CdS nanocrystals- an approach for enhancing the efficiency of inorganic- organic hybrid solar cell

Highly photoactive merocyanine 540 is revealed to form charge transfer complex with zinc sulphide and cadmium sulphide nanocrystals confirmed by FT-IR Spectroscopy, Fluorescence emission and UV-Visible spectrophotometer. The semiconducting nanocrystals were synthesized by co-precipitation method and characterized by Fluorescence emission spectroscopy, UV-Visible spectroscopy, Scanning electron microscopy (SEM), X-ray spectroscopy and Energy dispersive X-ray spectroscopy (EDAX). Merocyanine, in different concentrations was chemisorbed on the surface of ZnS and CdS nanomaterial. ZnS and CdS nanoparticles were used in hybrid solar cells in combination with organic polymer. These cells performed good efficiency at (6 × 10−6 M) dye concentration. The decreased power conversion efficiency with short circuit current density below and above the optimal merocyanine concentration (6 × 10−6 M) may be due to aggregation of merocyanine dye on CdS nanocrystals and subsequent self-quenching phenomena among dye molecules. The power conversion efficiency of the devices fabricated from P3HT-CdS-MC540 was higher than devices fabricated from P3HT-ZnS-MC540 because of particle size effect.

Influence of the interaction with DNA on the spectral-fluorescent and photochemical properties of some meso-substituted polymethine dyes

Spectral-fluorescent and photochemical properties of meso-substituted thiacarbocyanine dyes 3,3′-dimethyl-9-phenylthiacarbocyanine and 3,3′-diethyl-9-(2-hydroxy-4-methoxyphenyl)thiacarbocyanine in solutions and their interaction with DNA were studied. The dyes form noncovalent complexes with DNA, which is accompanied by changes in the absorption spectra and an increase in the fluorescence intensity of the dyes. The data obtained suggest that the dyes are in the form of trans-isomers both in solvents of different polarity and in complexes with DNA. It was shown that the interaction of the dyes with DNA is a complex process involving monomeric dye molecules and aggregates of the dyes. The primary photochemical processes of the dyes in solutions and in complexes with DNA were studied by flash photolysis technique. Upon flash photoexcitation in solutions, the formation and decay of the photoisomers of the dyes were observed, with no generation of the triplet states. In the complex with DNA, no signal of photoisomers was detected; in the absence of oxygen, the formation of the triplet state of the dyes was observed. The decay kinetics of the triplet state of the dyes were two-exponential. The process of quenching of the triplet state of the dyes by oxygen in a complex with DNA was studied, the respective quenching rate constants were estimated, being lower than the diffusion-controlled value.

Photoluminescence Spectroscopy of Rhodamine 800 Aqueous Solution and Dye-Doped Polymer Thin-Film: Concentration and Solvent Effects

This paper investigates solvent and concentration effects on photoluminescence (PL) or fluorescence properties of Rhodamine 800 (Rho800) dyes formed in aqueous solution and polymer thin-film. Various commonly used organic solvents including ethanol, methanol and cyclopentanol were studied at a constant dye concentration. There were small changes in the PL spectra for the different solvents in terms of PL intensity and peak wavelength. The highest PL intensity was observed for cyclopentanol and the lowest for ethanol. The longest peak wavelength was found in cyclopentanol (716 nm) and the shortest in methanol (708 nm). Dissolving the dye powder in the methanol solvent and varying the dye concentration in aqueous solution from the high concentrated solution to highly dilute states, the wavelength tunability was observed between about 700 nm in the dilute state and 730 nm at high concentration. Such a large shift may be attributed to the formation of dye aggregates. Rho800 dye-doped polyvinyl alcohol (PVA) polymer thin-film was further investigated. The PL intensity of the dye in the form of thin-film is lower than that of the aqueous solution form whereas the peak wavelength is redshifted due to the presence of PVA. This paper, to our best knowledge, reports the first study of spectroscopic properties of Rho800 dyes in various forms and provides useful guidelines for production of controllable organic luminescence sources.

Synthesis and biological imaging of cross-linked fluorescent polymeric nanoparticles with aggregation-induced emission characteristics based on the combination of RAFT polymerization and the Biginelli reaction

Fluorescent probes have long been regarded as tools for imaging living organisms with advantages such as high sensitivity, good designability and multifunctional potential. Many fluorescent probes, especially the probes based on aggregation-induced emission (AIE) dyes, have received increasing attention since the AIE phenomenon was discovered. These AIE dye-based fluorescent probes could elegantly overcome the notorious quenching effect caused by aggregation of conventional organic dyes. However, it is still difficult to directly apply these AIE-active dyes for biomedical applications owing to their hydrophobic nature. Therefore, the development of novel and facile strategies to endow them with water dispersibility is of critical importance. In this work, we exploit an efficient and simple strategy to fabricate an AIE dye-based fluorescent copolymer through the combination of reversible addition-fragmentation chain transfer and the Biginelli reaction. Moreover, the copolymer can self-assemble to fluorescent polymeric nanoparticles (FPNs) in water solution. Hydrophilic poly(PEGMA-co-AEMA) was reacted with the AIE-active dye 4′,4‴-(1,2-diphenylethene-1,2-diyl)bis([1,1′-biphenyl]-4-carbaldehyde (CHO-TPE-CHO) to form amphiphilic luminescent polymers using urea as the connection bridge. The successful synthesis of the final products (poly(PEGMA-co-AEMA-TPE) FPNs) was confirmed by various instruments. Furthermore, Transmission electron microscopy (TEM) images manifest that poly(PEGMA-co-AEMA-TPE) copolymers will self-assemble into spherical nanoparticles in aqueous environments with sizes between 100 nm and 200 nm. The cell uptake and bioimaging experiment confirm that poly(PEGMA-co-AEMA-TPE) FPNs have excellent biocompatibility and emit strong green fluorescence in a cellular environment. Thus, poly(PEGMA-co-AEMA-TPE) FPNs are excellent candidates for biomedical applications.

The role of ethanol-water solvent mixtures in N719 sensitization of electrodeposited ZnO nanorods

Water plays an important role in N719 sensitization of ZnO films for application as photoanodes in DSC devices. The role of water content in ethanolic N719 sensitization solutions was examined resorting to N719-solvent interaction studies based on Kamlet-Taft solvatochromic parameters. Results show that as the water content increases, solvent’s HBA ability decreases, hindering dye aggregation in solution and increasing the fraction of dye carboxylic groups available for anchorage onto the charged ZnO surface. The impact of dye-dye-solvent equilibria in solution on ZnO nanorod films sensitization and device behavior was evaluated. Devices assembled with films sensitized in N719 solutions containing equal parts of ethanol and water showed a twofold increase in short-circuit current densities when compared to those sensitized in ethanol only, despite exhibiting significantly less stained films. Data indicate that the presence of water in the sensitization solution reduces the amount of dye aggregates in solution and on the ZnO surface.

Optical determination of charge transfer times from indoline dyes to ZnO in solid state dye-sensitized solar cells

We studied the electron transfer at the interface of organic-inorganic hybrids consisting of indoline derivatives (D149 and D131) on ZnO substrates using a new optical method. We revealed the electron transfer times from the excited dye, e.g. the excitons formed in the dye aggregates to the ZnO substrate by analyzing the photoluminescence transients of the excitons after femtosecond excitation and applying kinetic model calculations. We reveal the changes of the electron transfer times by applying electrical bias. Pushing the Fermi energy of the ZnO substrate towards the excited dye level the transfer time gets longer and eventually the electron transfer is suppressed. The level alignment between the excited dye state and the ZnO Fermi-level is estimated. The excited state of D131 is about 100 meV higher than the respective state of D149 compared to the ZnO conduction band. This leads to shorter electron transfer times and eventually to higher quantum efficiencies of the solar cells.

Solvatochromic and nonlinear optical properties of Eosin B in solvents and AOT/water/Heptane

The third-order susceptibility and second-order hyperpolarizability and the two-photon absorption coefficient of Eosin-B in AOT/water/Heptane were investigated by using the Z-Scan technique. The droplets were prepared with an AOT/water droplet in a continuous phase of Heptane. The droplets size changes with the amount of water and the droplet concentration decreases with the increase of Heptane concentration. To study the nonlinear optical properties of Eosin-B, the Z-scan measurements were performed by means of a laser at 532 nm and 80 mW power. The nonlinear refractive and the nonlinear absorption coefficient indices were found to be in the order of 10−12 (cm2 W−1) and 10−7 (cm W−1), respectively. The change of nonlinear optical properties of Eosin-B by droplet size and concentration is due to the change of dye aggregation and thermal conductivity and thermo-optic coefficient of samples. The absorption of Eosin-B changes with the polarity of the medium (dielectric constant and refractive index). It has been shown that the intensity of emission spectra of Eosin-B in AOT/water/Heptane is enhanced compared to that of aqueous solution. By the Bilot and Kawski theory, the ratio between the excited state and the ground state of the dipole moments (μe/μg) of Eosin-B both in water and in droplets is extracted.

Influence of thermal annealing-induced molecular aggregation on film properties and photovoltaic performance of bulk heterojunction solar cells based on a squaraine dye

Squaraine (SQ) dyes have been considered as efficient photoactive materials for organic solar cells. In this work, we purposely controlled the molecular aggregation of an SQ dye, 2,4-bis[4-(N,N-dibutylamino)-2-dihydroxyphenyl] SQ (DBSQ-(OH)2) in the DBSQ(OH)2:[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend film by using the thermal annealing method, to study the influence of the molecular aggregation on film properties as well as the photovoltaic performance of DBSQ(OH)2:PCBM-based bulk heterojunction (BHJ) solar cells. Our results demonstrate that thermal annealing may change the aggregation behavior of DBSQ(OH)2 in the DBSQ(OH)2:PCBM film, and thus significantly influence the surface morphology, optical and electrical properties of the blend film, as well as the photovoltaic performance of DBSQ(OH)2:PCBM BHJ cells.

Crystallization and Aggregation-Induced Emission in a Series of Pyrrolidinylvinylquinoxaline Derivatives

Aggregation-induced emission (AIE) has been meanwhile observed for many dye classes and particularly for fluorophores containing propeller-like groups. Herein, we report on the AIE characteristics of a series of four hydrophobic pyrrolidinylvinylquinoxaline (PVQ) derivatives with phenyl, pyrrolyl, indolyl, and methoxythienyl substituents used to systematically vary the torsion angle between this substituent at the quinoxaline C2 position and the planar PVQ moiety. These molecules, which are accessible via four- or five-component one-pot syntheses, were spectroscopically studied in organic solvents and solvent–water mixtures, as dye aggregates, solids, and entrapped in polystyrene particles (PSP). Steady-state and time-resolved fluorescence measurements revealed a strong fluorescence enhancement for all dyes in ethanol–water mixtures of high water content, accompanying the formation of dye aggregates with sizes of a few hundred nm, overcoming polarity and H-bonding-induced fluorescence quenching of the cha...

Effect of terthiophene spacer position in Ru(II) bipyridyl complexes on the photocurrent and photovoltage for high efficiency dye-sensitized solar cells

Two novel ruthenium complexes, MR-1 and MR-2 were synthesized for use in dye-sensitized solar cells (DSSCs). Under similar fabrication conditions, the photovoltaic performances of these dyes were evaluated and compared to the standard ruthenium complex N719. MR-1 and MR-2 showed the efficiencies of 8.19% and 5.32%, respectively, while N719 achieved 7.66%. MR-1 also displayed higher VOC than MR-2, which is due to the larger molecular size and higher molar extinction coefficient of the former, which translates into less dye aggregation on a thinner film of TiO2. Incorporation of terthiophene as a linker reduces the band gap of MR-1 when compared to that of MR-2. The influence of π-conjugated bridge on optical and electrochemical properties was investigated. Results demonstrated that the absorption band of MR-1 displayed higher extinction coefficient with a broader absorption compared to MR-2 and the benchmark Ru(II) dye, N719, due to the enhancement of electron donating ability of π-conjugated bridge.

Chromonic self-assemblies in a series of dialkyl-thiacarbocyanine dyes and generalization of a facile route for the synthesis of fluorescent nanostructured silica fibers

Abstract In the search for new chromonic liquid crystals, we have explored the self-assembly behavior in water of a series of high-purity dialkylthiacarbocyanine dyes with different alkyl chain lengths and acetate as counterion. The dimer model was used to fit the UV–vis spectra and estimate the dissociation energy between molecules, which increases with the alkyl chain length suggesting that not only aromatic π–π interactions but also entropic/steric effects contribute to the aggregation process. NMR spectra suggest the existence of aromatic stacking interactions within the aggregates. At high concentrations, the dyes form nematic and hexagonal chromonic liquid crystals (CLC) in water within a limited range of alkyl chain lengths (ethyl to butyl); for longer lengths (pentyl) no liquid crystals were observed because of insufficient dye solubility. From small angle X-ray scattering patterns, it can be inferred that dye aggregates have cylindrical morphology with a multimolecular cross-section. The dye aggregates template the formation of silica nanofibers synthetized via sol–gel method in alkaline media. After removing excess dye, the silica/dye nanofibers showed high fluorescence emission with superb photochemical stability. The present report demonstrates a generalized route for the wet synthesis of nanostructured silica nanofibers with tunable optical properties.

Increased Efficiency of Dye‐Sensitized Solar Cells by Incorporation of a π Spacer in Donor–Acceptor Zinc Porphyrins Bearing Cyanoacrylic Acid as an Anchoring Group

Two novel porphyrins, ZnP(SP)CNCOOH and ZnPCNCOOH, bearing cyanoacrylic acid as an anchoring group were synthesized. Porphyrin ZnP(SP)CNCOOH contains a π‐conjugated spacer (SP) for improved electronic communication between the dye and the TiO2 electrode. The spacer bears polyethylene glycol chains to prevent dye aggregation and to enhance solubility of the dye. Electrochemical measurements and theoretical calculations suggest that both porphyrins are promising sensitizers for dye‐sensitized solar cells (DSSCs), as their molecular orbital energy levels favor electron injection and dye regeneration. Solar cells sensitized by ZnP(SP)CNCOOH and ZnPCNCOOH show power conversion efficiencies of 7.61 and 5.02 %, respectively. Photovoltaic measurements (J–V curves and incident photon to current conversion efficiency spectra) show that higher short‐circuit current (Jsc) and open‐circuit voltage (Voc) values are reached for the solar cell based on ZnP(SP)CNCOOH. This can be mainly ascribed to suppressed charge recombination, as indicated by their electrochemical impedance spectra.

Effects of Dye Surface Concentration on the Molecular Aggregation of Xanthene Dye in Colloidal Dispersions of Montmorillonite

AbstractThe molecular aggregation of organic dyes onto clay mineral particles is a very complex phenomenon including dye adsorption, the migration of dye molecules, rearrangement of initially formed aggregates, etc. Some details of this complex process are not yet fully understood. The objective of the present study was to understand the influence of dye surface concentration on the dynamic processes in dye molecular aggregation. A stopped-flow rapid mixing device was used for accurate measurements of the molecular aggregation of the cationic dye rhodamine 123 (R123) in montmorillonite (MntK) colloidal dispersions. The influence of dye surface concentration, which was changed by altering the ratio of the amount of R123 to the mass of MntK (nR123/mMntK), was examined in detail. Chemometric analysis was used to reconstruct the spectral matrix to obtain linearly uncorrelated spectral profiles of the major components and their concentrations at the respective reaction times. The conversion of isolated R123 cations into oblique J-aggregates (head-to-tail molecular assemblies) was observed over time and the existence of a J-dimers intermediate was hypothesized. The reaction kinetics followed a biphasic exponential function. An unexpected effect of dye surface concentration on R123 aggregation was observed: the initial formation of the molecular aggregates increased significantly with dye surface concentration, but an inverse trend was observed after longer reaction times. While dye aggregates were formed slowly at low dye loadings, systems with high R123/MntK ratios (nR123/mMntK) reached spectral stability after the first few seconds of the reaction. After longer reaction times, the greatest degree of dye aggregation was achieved in the dispersion of the lowest dye loading. Such a phenomenon is described for the first time. The results presented here are important for understanding the complex processes occurring in systems based on organic cations and clay minerals, and should be considered in the development of functional hybrid materials of dyes and nanoparticles with a layered structure.

Tuning the Photophysical Properties of Cyanine Dyes with Clay Minerals

AbstractDye molecular aggregation and other interactions on clay mineral surfaces cause phenomena such as methachromasy (change in color), fluorescence enhancement, or quenching, which represent significant changes in the spectral properties of the dye. These phenomena can be used to control the photophysical properties of hybrid systems based on cationic organic dyes. In the present study, the aggregation of two structurally similar cyanine dyes, 3,3’-diethyl-oxocyanine iodide (OxCy) and 3,3’-diethyl-2,2’-thiacyanine iodide (ThCy), in colloidal dispersions of three smectites (saponite, hectorite, and montmorillonite) was studied by absorption and fluorescence spectroscopy for a broad range of dye/smectite loadings. Spectral data were analysed by chemometric methods (principal component analysis, PCA, and multivariate curve resolution, MCR). Detailed analysis of the OxCy absorption spectra by the chemometric methods revealed the formation of two types of oblique aggregates exhibiting light absorption in both H- and J-bands. The existence of such similar aggregates, with similar splitting of excitation energies, appears to be related to the existence of two stable conformational isomers of this dye. On increasing the smectite CEC and dye/smectite loading, fluorescence quenching occurred. The ThCy dye exhibited a stronger tendency for molecular aggregation than OxCy. On increasing the smectite CEC, the formation of oblique aggregates with dominant H-bands also increased. On aging of the hybrid dispersions, equilibria of ThCy aggregates were shifted to the species with dominant J-bands. This behavior had a significant impact on the shape and intensity of the fluorescence emission of the hybrid dispersions. Using different smectites enables control of the dye aggregation and significant change to the photophysical properties of the hybrid systems. These systems can be used for the detailed study of the photophysical properties of cyanine dyes in various states. The colloidal systems with cyanine dyes can be used as precursors for the preparation of novel hybrid materials. In addition, the sensitive response of the photophysical properties of cyanine dyes to the clay mineral surface can be applied to the characterization of clay minerals.

BEHAVIOURE STUDY OF THE ASSOCIATION BETWEEN ACID-BASE INDICATORS IN ACIDIC MEDIUM BY USING SPECTROSCOPY TECHNIQUE

تمت دراسة سلوك الارتباط بين مؤشرات القاعدة الحمضية في المحلول المائي المخزن (pH = 4) بواسطة تقنية التحليل الطيفي UV-Vis في درجة حرارة الغرفة. أظهرت نتائج التحليل الطيفي أن الارتباط يتشكل من خلال تحول أحمر شديد إلى max = 485 نانومتر وتغير كبير للكروم في إشارة الامتصاص عند إضافة صبغة سابقة. تمت مناقشة أطياف الامتصاص الإلكتروني المتمثلة في نطاقات التوسيع وعدم وجود نقطة متساوية التي تشير إلى تكوين مجاميع صبغية أعلى مرتبة من النوع J-الكلي كنتيجة كتغير في الأس الهيدروجيني للوسط تمت مناقشته وفقًا لنظرية exciton kasha.

Synthetic talc as a new platform for producing fluorescent clay polyurethane nanocomposites

As a non-swelling clay, talc generally interacts very weakly with organic molecules. However, two new nanometric synthetic talcs that incorporate berberine chloride were successfully used as fluorescent fillers in clay polyurethane nanocomposites obtained by the blending method. A micrometric natural talc filler was also used for comparison. The clay polymer nanocomposites (CPN) were characterized by FTIR, molar mass analysis and XRD. All talc fillers were well dispersed into the polyurethane matrix even at high filler content of 5 wt%, as supported by TEM and SEM analyses. Morphological changes were confirmed by AFM. The optical properties of the fluorescent talcs, dye-doped polymer and CPN were compared. While the dye-doped polymer suffered from conventional fluorescence quenching due to dye aggregation, the emission quantum yield of the CPN was increased with increasing the filler content. The best emission efficiency was observed for the CPN that contains the smallest talc-berberine hybrid particles. The use of fluorescent synthetic talc resulted in materials with good thermal and mechanical properties, and can be considered as a new method to produce fluorescent CPN in view of multiple applications.

Co-sensitization of ruthenium(II) dye-sensitized solar cells by coumarin based dyes

Co-sensitization technique has been appraised for attaining enhanced performance in dye-sensitized solar cells (DSSCs). DSSCs are fabricated with a heteroleptic Ru(II) sensitizer (RDAB1) containing 4,4′-diamino-2,2′-bipyridine (dabpy) ligand, co-sensitized with electron donor–acceptor type coumarin containing thiophene (CT) and indole (CI) moieties. The individual overall power conversion efficiency of the sensitizer is 5.44%. Enhanced power conversion efficiencies of 6.34% and 7.09% were observed when RDAB1 was co-sensitized with Coumarin containing CI and CT respectively. The enhanced PCE can be attributed to the presence of co-sensitizers which effectively overcome the light absorption by I−/I3−, dye aggregation and charge recombination.

Enhanced performance of ZnO-based dye-sensitized solar cells by glucose treatment

Hierarchical ZnO nanosheet-clusters as three-dimensional ZnO photoanodes with surface modification have been achieved via a facile and simple immersion method in glucose solution at room temperature for dye-sensitized solar cells. The surface properties of glucose-modified ZnO nanosheets are analyzed by X-ray photoelectron spectra and transmission electron microscopy. The current-voltage curve measurements show that the dye-sensitized solar cell with an immersion time of 2 min illustrates the best photoelectrochemical performance of 5.31%, which can be attributed to the prevention of the dye aggregation and the large recombination resistance resulting from the self-assembled glucose molecules on ZnO surfaces. From the modulated photo-voltage spectroscopy and intensity modulated photocurrent spectroscopy measurements further illustrate that the glucose-modified ZnO photoanodes possess large electron lifetime and long electron diffusion length. The glucose-modified ZnO nanosheet surfaces not only provide a three-dimensional structure but also avoid extensive Zn2+/dye complexes formation. The findings from our work are important for the design of efficient photoanode materials with superior performance for dye-sensitized solar cells.

J-Aggregates of Indoheptamethine Cyanine Dye

The effect of doubly charged inorganic and organic cations on the aggregation of anionic indoheptamethine cyanine dyes has been studied in aqueous solutions. It is shown that the effective formation of J-aggregates with narrow exciton absorption bands in the IR region of the spectrum with λmax = 920 nm is characteristic only of a dye with SO 3 - groups in the 6,6′-positions of the benzoindolenine ring. It is found that bis-quaternary salt based on α-picolinium is particularly effective as a J-aggregating agent and causes J-aggregation at a concentration close to the dye concentration. It follows that the introduction of sulfogroups at the 6,6′-positions of the benzoindolenine ring creates optimal conditions for packing the molecules of the indolenine dye into a highly organized structure of a “brickwork” type under the action of multiply charged cations. It is shown that the J-aggregates of the indoheptamethine cyanine dye are photoelectric converters for the IR region of the spectrum.