Dye Aggregation Research Articles

The Aggregates of Near-Infrared Cyanine Dyes in Phototherapy.

Cyanines in the near-infrared region are a typical example of a classic fluorescent dye that has garnered significant attention and widespread use in the life sciences and biotechnology. Their character to form assemblies or aggregates has inspired the development of various functional cyanine dye aggregates in phototherapy. This article provides a brief summary of the strategies used to prepare these cyanine dye aggregates. The reports in this concept suggest that the self-assembly of cyanine dyes can enhance their photostability, opening up new possibilities for their application in phototherapy. This concept may encourage researchers to explore the development of functional fluorescent dye aggregates further.

Electronic Structure and Excited-State Dynamics of DNA-Templated Monomers and Aggregates of Asymmetric Polymethine Dyes.

Aggregates of conjugated organic molecules (i.e., dyes) may exhibit relatively large one- and two-exciton interaction energies, which has motivated theoretical studies on their potential use in quantum information science (QIS). In practice, one way of realizing large one- and two-exciton interaction energies is by maximizing the transition dipole moment (μ) and difference static dipole moment (Δd) of the constituent dyes. In this work, we characterized the electronic structure and excited-state dynamics of monomers and aggregates of four asymmetric polymethine dyes templated via DNA. Using steady-state and time-resolved absorption and fluorescence spectroscopy along with quantum-chemical calculations, we found the asymmetric polymethine dye monomers exhibited a large μ, an appreciable Δd, and a long excited-state lifetime (τp). We formed dimers of all four dyes and observed that one dye, Dy 754, displayed the strongest propensity for aggregation and exciton delocalization. Motivated by these results, we undertook a more comprehensive survey of Dy 754 dimer and tetramer aggregates using steady-state absorption and circular dichroism spectroscopy. Modeling these spectra revealed an appreciable excitonic hopping parameter (J). Lastly, we used femtosecond transient absorption spectroscopy to characterize τp of the dimer and tetramer, which we observed to be exceedingly short. This work revealed that asymmetric polymethine dyes exhibited μ, Δd, monomer τp, and J values promising for QIS; however, further work is needed to overcome excited-state quenching and achieve long aggregate τp.

Design and Synthesis of Novel NIR‐Sensitive Unsymmetrical Squaraine Dyes for Molecular Photovoltaics

Two novel near‐infrared (NIR)‐sensitive unsymmetrical squaraine dyes, SQ‐258 and SQ‐259, for their suitability as a sensitizer in dye‐sensitized solar cells (DSSCs) are designed and synthesized, followed by photophysical and photovoltaic characterizations. It is demonstrated that introducing a 1,3‐indandione acceptor unit in the central squaric acid core of SQ‐259 leads to the suppression of dye aggregation owing to its nonplanar molecular geometry and the broadening of the optical absorption and photon‐harvesting window up to 800 nm. Owing to the extended wavelength photon harvesting, SQ‐259 improves the photoconversion efficiency (PCE) compared to its SQ‐258 dye counterpart. However, despite its wide wavelength photon harvesting, the improvement in the PCE of SQ‐259 is less pronounced, and this is attributed to the small driving force for injection of electrons (0.29 eV), hampered electronic coupling, and decreased electron lifetime for resistance to recombination (7.9 ms), which is confirmed by the cyclic voltammetry, quantum chemical calculation, and electrochemical impedance spectroscopic investigations, respectively.

Aggregates of Cyanine Dyes: When Molecular Vibrations and Electrostatic Screening Make the Difference.

Aggregates of cyanine dyes are currently investigated as promising materials for advanced electronic and photonic applications. The spectral properties of aggregates of cyanine dyes can be tuned by altering the supramolecular packing, which is affected by the length of the dye, the presence of alkyl chains, or the nature of the counterions. In this work, we present a joint experimental and theoretical study of a family of cyanine dyes forming aggregates of different types according to the length of the polymethinic chain. Linear and nonlinear optical spectra of aggregates are rationalized here in terms of an essential-state model accounting for intermolecular interactions together with the molecular polarizability and vibronic coupling. A strategy is implemented to properly account for screening effects, distinguishing between electrostatic intermolecular interactions relevant to the ground state (mean-field effect) and the interactions relevant to the excited states (excitonic effects). To the best of our knowledge, this is the first attempt to simulate nonlinear spectral properties of aggregates of symmetric dyes accounting for molecular vibrations.

Transparent Wood Biocomposite of Well-Dispersed Dye Content for Fluorescence and Lasing Applications.

Aggregation-induced quenching often restricts emissive performance of optically active solid materials with embedded fluorescent dyes. Delignified and nanoporous wood readily adsorbs organic dyes and is investigated as a host material for rhodamine 6G (R6G). High concentration of R6G (>35 mM) is achieved in delignified wood without any ground-state dye aggregation. To evaluate emissive performance, a solid-state random dye laser is prepared using the dye-doped wood substrates. The performance in terms of lasing threshold and efficiency was improved with increased dye content due to the ability of delignified wood to disperse R6G.

Highly efficient labelling of extracellular vesicles for enhanced detection on a microfluidic platform

Developing precise extracellular vesicles (EVs) labelling techniques with minimal disturbance is of great importance to the follow-up EVs detection and analysis. However, currently available methods such as using probes to conjugate phospholipids or membrane proteins have certain limitations due to EV steric hindrance, dye aggregation, etc. Here, we present a microfluidic platform to enhance EVs’ labelling efficiency and improve their detection. This platform provides excellent sample throughput and high-efficiency EV labelling at lower label concentrations with an optimized flowing rate. Flow cytometry analysis (FCM) and cellular uptake results show that EV labelling by utilizing this platform possesses the merits of a higher labelling efficiency with 64.1% relative improvement than conventional co-incubation method and a lower background noise. Moreover, this technique maintains EVs’ size, morphology and biological activities. After the recipient cells uptake the EVs treated by the microfluidic platform, the spatial and temporal distribution of EVs in the cells are clearly observed. These results demonstrate that our method holds great potential in efficient labelling of EVs, which is essential to subsequent EV quantification and analysis.

Enhancement of Fluorescence Mediated by Silver Nanoparticles: Implications for Cell Imaging.

In this study, we report the surface enhanced fluorescence (SEF) of a biologically important organic dye, fluorescein (FL), by silver nanoparticles (Ag NPs) in an aqueous medium and its implications for human cell imaging. The as-synthesized Ag NPs were characterized by dynamic light scattering (DLS), zeta potential, transmission electron microscopy (TEM), and UV-vis absorption spectroscopic studies. The interaction and aggregation of FL dye with Ag NPs and a cationic surfactant, namely, cetyltrimethylammonium bromide (CTAB), were explored by UV-vis absorption and steady-state and time-resolved fluorescence spectroscopic methods. The distance-dependent fluorescence enhancement of FL due to Ag NPs in the solution was also theoretically correlated by three-dimensional finite-difference time-domain (3D-FDTD) simulation. The plasmonic coupling between neighboring NPs facilitated the augmentation of the local electric field, thereby producing various "hotspots" that influence the overall fluorescence of the emitter. J-type aggregates of FL in the presence of the CTAB micelles and Ag NP mixed solution were confirmed by electronic spectroscopy. The density functional theoretical (DFT) study revealed the electronic energy levels associated with different forms of FL dye in the aqueous solution. Most interestingly, the Ag NP/FL mixed system used in fluorescence imaging of human lung fibroblast cells (WI 38 cell line) showed a significantly stronger green fluorescence signal compared to that of FL after an incubation period of only 3 h. This study confirms that the Ag NP mediated SEF phenomenon of the FL dye is also manifested in the intracellular medium of human cells giving a brighter and more intense fluorescence image. The cell viability test after exposure to the Ag NP/FL mixed system was confirmed by the MTT assay method. The proposed study may have an implication as an alternate approach for human cell imaging with higher resolution and more contrast.

Optoelectronic properties fine-tuning through chalcogenide-based π-bridge for dye molecules featuring hydantoin anchoring group: first-principle calculations

This study investigates the effect of chalcogenides and electron-withdrawing groups CN and F on the optoelectronic properties using DFT and TD-DFT methods, with a focus on the use of a hydantoin anchoring group as an alternative to carboxylic acid-based groups. The results show that the studied dyes have a planar structure that facilitates intramolecular charge transfer and that propeller-shaped terminal phenyl rings help reduce dye aggregation. The maximum absorption was observed between 485 and 627 nanometres, and bathochromic shifts in UV-Vis spectra were observed in the order NH, S, O, Se, and Te for both F- and CN-containing dyes. Excited-state lifetime was highest for dyes containing heavier chalcogenides. Adsorption energies of the dye onto TiO2 anatase (101) with 3 × 6 supercell were found in the range of 0.13–0.79 eV and 0.61–1.54 eV for CN and F-containing dyes, respectively. Dyes featuring Se and Te exhibit superior properties for dye-sensitized solar cell application, and chalcogenide-based dyes are worthy of experimental synthesis. Overall, the study provides valuable insights into the optoelectronic properties of dyes and their potential use in more efficient solar cell technologies.

First Observation of Protomicelles in the System with a Non-Colloidal Surfactant

A spectrophotometric study of the system heptanol—Nile red (NR)—water was carried out, where, for the first time for such studies, a non-colloidal surfactant that does not form micelles was taken as a surfactant. The dependence of the solubility of NR on the concentration of heptanol in an aqueous solution was studied. The experiments were carried out at a given chemical potential of NR, which was provided by an excess of the solid phase of NR. The existence of a solubilization effect has been theoretically and experimentally established: An increase in the solubility of NR with an increase in the concentration of heptanol in solution. It was found that heptanol protomicelles with a solubilization core as an NR molecule are formed in such a system, so that in the absence of micelles, the protomicelles take on the entire solubilization load. From the experimental data, the concentration of protomicelle formation was calculated, which can also be taken as the concentration of NR monomerization in an aqueous solution, since the formation of protomicelles prevents the dye aggregation. Based on the results obtained, the following generalizations were made: (1) non-colloidal surfactants, although they do not give micelles, are capable of forming protomicelles; and (2) non-colloidal surfactants can serve as a practical means of dye monomerization.

Silver doped ZnSnO3/SnO hybrid nanostructures as DSSC photoanodes: Charge injection dynamics, slow recombination kinetics and simulation studies

Sol-gel synthesis was used to develop a new hybrid photoanode material, a spherical zinc stannate/tin oxide nanorod named ZSTP. The subsequent step involves doping ZSTP with silver using a precursor called silver nitrate. The undoped sample was labelled as ZSTP, whereas silver-doped composites containing 1, 2, and 3 wt% silver were labelled as ZSTP-Ag1, ZSTP-Ag2 and ZSTP-Ag3 respectively. The pattern of powder X-ray diffraction (PXRD) with 2θ values of 26.52 and 33.84 confirms the orthorhombic structure of ZSTP and silver-doped samples. In the FT-IR spectra of the ZSTP and their silver-doped samples, the stretching frequency for Zn–O–Sn is observed at 1100 and 1464 cm−1. In addition, the surface-adsorbed Ag peaks at 1384 cm−1. The XPS spectra of ZSTP-Ag3 confirms the existence and structure of SnO and Ag. Examining the morphology with a scanning electron microscope (SEM) and transmission electron microscope (TEM) reveals a porous structure with adsorbed Ag on the surface. Doped silver appears as tiny spherical particles on the surfaces, whereas SnO nanorod zinc stannate appears as spherical particles in the TEM image. In-depth optical experiments were conducted to evaluate the characteristics of hybrid composites for DSSC applications. It was explored how the dye aggregates on the surface of silver-doped ZSTP. On the basis of the energy levels of their conductance bands, the electron transfer kinetics and energy transfer mechanism were predicted. Under a conventional one-sun illumination condition, the output photocurrent and photovoltage of these DSSC materials are evaluated. ZSTP-Ag3 offered the highest PCE at 1.38%. Due to the role of Ag2O in electron transfer, silver doped samples based devices offer a high FF (0.7) and steady photovoltage. Using the photovoltage decay curve, the recombination time (τrec) and rate (krec) were calculated to confirm a slower rate of recombination. Using simulated results, the overall performance of the DSSC is compared and validated.

Dye disaggregation light-up aptamer for super-resolution RNA imaging

Genetically encoded light-up RNA aptamers have become powerful tools for visualizing RNAs in cells. However, fluorogenic dye/aptamer pairs used for super-resolution RNA imaging are still rare. Herein, we reported an environment-sensitive dye Nap which can light up its target RNA aptamer NapRA for aptamer-based RNA imaging with confocal and structured illumination microscopy (SIM). Nap was designed to be amphiphilic to assemble into nano-particles in water associated with the quenched fluorescence by the aggregation effects. NapRA was obtained from SELEX technology with a 12-round Nap-based selection and has a high binding affinity to Nap of Kd = 3.142 nM. The super affinity disintegrated the dye aggregate and resulted in a turn-on fluorescent signal. The light-up feature combined with high photostability made Nap/NapRA a useful system capable of super-resolution imaging of the expression of RNA in bacteria. This work represents the first application of dye aggregation-disaggregation for aptamer-based RNA imaging.

Chemorobust dye-encapsulated framework as dual-emission self-calibrating ratiometric sensor for intelligent detection of toluene exposure biomarker in urine

By taking advantages of confinement effect can effectively prevent dye aggregation caused luminescent quenching, Eosin Y (EY) was encapsulated into a chemorobust porous CoMOF as secondary fluorescent signal to construct the dual-emitting sensor of EY@CoMOF. And the photo-induced electron transfer from CoMOF to EY molecules induced EY@CoMOF presenting a weak blue emission at 421 nm and a strong yellow emission at 565 nm. Those dual-emission features also endow EY@CoMOF itself great potentials as a self-calibrating ratiometric sensor in visually and efficiently monitoring hippuric acid (HA) in urine, with fast response, high sensitivity and selectivity, excellent recyclable, and low LOD (0.24 μg/mL). Furthermore, based on a tandem combinational logic gate, an intelligent detection system was designed to improve the practicability and convenience of HA detection in urine. To the best of our knowledge, this is the first example of dye@MOF based sensor for HA detection. And this work provides a promising approach for developing dye@MOF based sensors to intelligent detect bioactive molecules.

Aggregation Triggers Red/Near-Infrared Light Hydrogen Production of Organic Dyes with High Efficiency

Integrating broad-band red/near-infrared (NIR) light harvesting and efficient charge separation in a semiconductor is a crucial prerequisite for the realization of high photocatalytic efficiency but remains a challenge. Here, we discover that eosin Y (EY) aggregates exhibit strong red/NIR-light harvesting induced by electronic couplings between adjacent EY molecules. Simultaneously, the aggregates are favorable for exciton dissociation and formation of charge-separation states, greatly inhibiting charge recombination. The quantum yield (QY) of EY aggregates for hydrogen production highly reaches 23.6% at 610 nm. More importantly, this general concept of aggregation-induced red/NIR-light photocatalysis was observed in a series of typical organic dyes (11 examples). Impressively, the QY of cobalt phthalocyanin aggregates for hydrogen production is calculated to be 17.2% at 800 nm, which is the highest value among NIR-light-driven H2-evolution systems (≥800 nm) ever reported. This study unlocks a fresh realm of artificial photosynthesis, which uses dye aggregates for red/NIR-light solar conversion.

Effect of Substituent Location on the Relationship between the Transition Dipole Moments, Difference Static Dipole, and Hydrophobicity in Squaraine Dyes for Quantum Information Devices.

Aggregates of organic dyes that exhibit excitonic coupling have a wide array of applications, including medical imaging, organic photovoltaics, and quantum information devices. The optical properties of a dye monomer, as a basis of dye aggregate, can be modified to strengthen excitonic coupling. Squaraine (SQ) dyes are attractive for those applications due to their strong absorbance peak in the visible range. While the effects of substituent types on the optical properties of SQ dyes have been previously examined, the effects of various substituent locations have not yet been investigated. In this study, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were used to investigate the relationships between SQ substituent location and several key properties of the performance of dye aggregate systems, namely, difference static dipole (Δd), transition dipole moment (μ), hydrophobicity, and the angle (θ) between Δd and μ. We found that attaching substituents along the long axis of the dye could increase μ while placement off the long axis was shown to increase Δd and reduce θ. The reduction in θ is largely due to a change in the direction of Δd as the direction of μ is not significantly affected by substituent position. Hydrophobicity decreases when electron-donating substituents are located close to the nitrogen of the indolenine ring. These results provide insight into the structure-property relationships of SQ dyes and guide the design of dye monomers for aggregate systems with desired properties and performance.

Cast, Dip, Spray, and Print─Covalently Embedded Photochromic Materials from a Versatile Spiropyran Conjugate

Dynamic photochromic dyes are in great demand for various applications. These are used as active materials with tunable optical properties. However, producing photochromic materials in significant quantities is still a challenge. The ability to retain and prolong the interconversion of switching between open and closed forms is affected by undesirable aggregation of dyes in the matrix. The often-employed method of adding photochromic dyes into bulk materials causes issues such as aggregation, leaching of dye, and photoinstability. A versatile light-responsive spiropyran substituted azo-initiator was conveniently synthesized and utilized for incorporating photochromic units at the α-chain end of the vinyl polymers. Accordingly, processes in bulk, solution, and emulsion/dispersion were developed by radical polymerization of common vinyl monomers such as styrene and acrylates. This approach enabled the preparation of light-responsive polymers possessing photochromic spiropyran units covalently incorporated at the polymer chain end. Thus, monodisperse, covalently embedded photochromic colloidal particles with low dye content (<0.1 mmol) were prepared. The fabrication and high-resolution spatiotemporal control of materials such as gels, elastomers, resins, and transparent films of commodity polymers embedded with photochromic units are demonstrated with detailed coloring, fading, and fatigue behavior. The facile and straightforward approach developed to prepare photochromic colloidal particles can be applied to any substrate through cast, dip, spray, or print to make “smart” photochromic materials.

Theoretical Design of New Healthy Organic Dyes for Solar Cell Applications with Favorite Medicinal Effect

In this work, a computational investigation was used to design and study new materials based on carminic acid isomers as organic dyes for DSSCs. Density functional theory (DFT) was applied to report the ground state and the excited state characteristic was reported by utilizing time-dependent DFT (TDDFT) methods. Some electronic, optical, photolytic and electron transfer properties are evaluated to achieve our study. The results indicate that modifying the chemical structure of a dye by doping improves light harvesting efficiency while reducing the driving force for electron injection and the potential of dye renewal while boosting dye aggregation on the electrode surface. The new structures dyes displays strong charge transfer absorption bands in the visible, excellent electronic, sufficient driving force and photoelectric conversion efficiency in comparison with carminic acid. Also, All suggested dyes have sufficient properties to achieve high PCE of the DSSCs. These results are adequate for a potential effective electron injection process. Accordingly, the theoretical methods are significant to provide experimental methods for designing new, highly efficient materials for optoelectronic applications. It was found that these dyes do not have any medical effect on human health.

Features of cyanine dyes aggregation on differently charged TiO2 matrices

Changing the polycondensation reaction route, positively and negatively charged TiO2 nanoparticles have been synthesized. On the base of the synthesized TiO2 nanoparticles, porous TiO2 films have been formed with different surface charges. J-aggregates of two anionic dyes were formed on positively charged TiO2 films, while J-aggregates of cationic dye was formed on negatively charged one. Combining J-aggregates with different J-band spectral positions, we have obtained two composites consisting of J-aggregates pairs with an effective excitation energy transfer between them. In both cases, simple mixing of J-aggregate in solution did not result in the composite formation and only sequential deposition of J-aggregate from corresponding solutions was successful. Interesting, not only charge alternating composite of cationic pseudoisocyanine J-aggregates and anionic thiacarbocyanine J-aggregates was realized, but also the same was done in the case of the composite of two anionic carbocyanine J-aggregates.

Variety of steady and excited state interactions in BODIPY aggregates: Photophysics in antisolvent systems and floating layers

Associative behavior of geometrically anisotropic meso-(4-octadecyloxy-phenyl)-boron-dipyrrin (BODIPY) studied spectroscopically in binary solvent mixtures and upon compression in Langmuir floating layers. Different steady and excited state species were found upon monolayer compression and facilitated aggregation in water/ acetonitrile systems. This discrepancy points to a big concern in possibility of commonly applied generalizations across different aggregating systems. Broad range of decay fitting models were examined to reveal their benefits and pitfalls specific to examination of dye aggregates. Radiative constant gamma-distribution approach and free form fluorescence lifetime distribution with maximum entropy method (MEM) outperformed multiple common techniques for analysis of complex fluorescence decays. MEM could be recommended for analysis of systems where complicated lifetime distributions appear over time or upon external stimuli. Findings and protocols could be utilized as tools in studies of steady and excited-state photophysics of BODIPY aggregates.

A versatile vessel casting method for fine mapping of vascular networks using a hydrogel-based lipophilic dye solution

Efficient labeling of the vasculature is important for understanding the organization of vascular networks. Here, we propose VALID, a vessel-labeling method that enables visualization of vascular networks with tissue clearing and light-sheet microscopy. VALID transforms traditional lipophilic dye solution into hydrogel by introducing gelatin and restrains the dye aggregation, resulting in complete and uniform vessel-labeling patterns with high signal-to-background ratios. VALID also enhances the compatibility of lipophilic dyes with solvent-based tissue-clearing protocols, which was hard to achieve previously. Using VALID, we combined lipophilic dyes with solvent-based tissue-clearing techniques to perform 3D reconstructions of vasculature within mouse brain and spinal cord. We also employed VALID for 3D visualization and quantification of microvascular damage in a middle cerebral artery occlusion mouse model. VALID should provide a simple, cost-effective vessel-labeling protocol that would significantly widen the applications of lipophilic dyes in research on cerebrovascular complications.

Intramolecular Charge Transfer and Ultrafast Nonradiative Decay in DNA-Tethered Asymmetric Nitro- and Dimethylamino-Substituted Squaraines.

Molecular (dye) aggregates are a materials platform of interest in light harvesting, organic optoelectronics, and nanoscale computing, including quantum information science (QIS). Strong excitonic interactions between dyes are key to their use in QIS; critically, properties of the individual dyes govern the extent of these interactions. In this work, the electronic structure and excited-state dynamics of a series of indolenine-based squaraine dyes incorporating dimethylamino (electron donating) and/or nitro (electron withdrawing) substituents, so-called asymmetric dyes, were characterized. The dyes were covalently tethered to DNA Holliday junctions to suppress aggregation and permit characterization of their monomer photophysics. A combination of density functional theory and steady-state absorption spectroscopy shows that the difference static dipole moment (Δd) successively increases with the addition of these substituents while simultaneously maintaining a large transition dipole moment (μ). Steady-state fluorescence and time-resolved absorption and fluorescence spectroscopies uncover a significant nonradiative decay pathway in the asymmetrically substituted dyes that drastically reduces their excited-state lifetime (τ). This work indicates that Δd can indeed be increased by functionalizing dyes with electron donating and withdrawing substituents and that, in certain classes of dyes such as these asymmetric squaraines, strategies may be needed to ensure long τ, e.g., by rigidifying the π-conjugated network.