Solvatochromic Dyes Research Articles

Tracking a Homeopathic Complex Formulation in the Watercourses of a Fire-Damaged State Park in Brazil.

In 2020, a 26,849-ha state park in Mato Grosso do Sul state, Brazil, had 30% of its area damaged by fire. A homeopathic complex formulation was applied at strategic point locations in the park's springs or watercourses, aiming to mitigate the fire damage to the flora and fauna as quickly as possible. The duration of the homeopathic signal at each point was assessed using an established solvatochromic dye technique. To evaluate the timing and the nature of the signal at each of nine point locations. We could thus identify the presence of any signal variations due to specified environmental features within the park. Water samples were harvested from each intervention point at different times, filtered, frozen, and sent to the laboratory, where they were prepared to 1cH using filtered 30% ethanol. Methylene violet was chosen among six dyes since it was found in preliminary tests that it could trace the homeopathic complex used. In addition to simple sample testing, samples were submitted to a static and unidirectional magnetic field of 2400 Gauss (240 mT) for 15 minutes immediately before reading, which enhanced the method's sensitivity. One-way analysis of variance/Tukey test was used to identify dye absorbance changes following the analysis of water samples from the watercourse system. A correlation matrix and the Spearman r test were employed to evaluate any correlation between tracking and the pre-existing anthropic interventions at harvesting points. In all cases, α = 0.05. Four tracking patterns using the sample magnetization process were observed in relation to water samples and their effect on methylene violet solutions: no response (P2, P4), early transitory response (P5, P6, P8), late response (P1, P9), and constant response (P3, P7). P2 and P4, which could not be tracked, were correlated with permanent local anthropic disturbance. Methylene violet was the best dye to track the homeopathic complex prepared specifically for this case. Tracking was facilitated by prior magnetic treatment of samples, but anthropic disturbances to the environment seem to interfere with it.

Solvatochromic Dyes Track a Homeopathic Preparation through Water-Stream Systems in a Program to Control Tick Infestation at a Wild Animal Rehabilitation Center in Brazil.

In 2021, the area of CRAS (Centro de Reabilitação de Animais Selvagens - Wild Animal Rehabilitation Center), located in a state park in Campo Grande City, Mato Grosso do Sul, Brazil, was suffering from a tick infestation affecting wild animals that inhabit the area and humans that visited its trails. Following a formal technical-scientific cooperation agreement between IMASUL, an institute for the environment in Mato Grosso do Sul state, and SIGO Homeopatia, a formulated homeopathic complex (Formula Parques Urbanos, FPU) was designed and prepared specifically to treat the animals. This environmental intervention used specially designed slow-release water biodegradable devices. Tracking the FPU signal in water was necessary to monitor and manage the intervention. Our aims were (1) to evaluate, among six previously standardized solvatochromic dyes, which would serve as a marker for the homeopathic complex under study; and (2) to evaluate whether the chosen solvatochromic dye could map the propagation of the homeopathic complex activity throughout the stream system from water samples harvested at different locations over time. Water samples were harvested from each point at different times, filtered, frozen, and sent to the laboratory, where they were prepared at 1cH potency for analysis using 30% ethanol as the vehicle. Solvatochromic dyes were used to analyze the samples since they alter their absorbance when in contact with homeopathic potencies. Of the six dyes tested, Coumarin 7 was found to be the most suitable for tracking the FPU complex. A static and average unidirectional magnetic field of 2,400 Gauss (240 mT), generated by a neodymium magnet, was applied to the samples immediately before reading. There were significant differences in the delta absorbance of dyes when adding treated/potentized water samples, making it possible to map the propagation of the FPU signal throughout the park over time. The signals were identifiable at the same point 1 minute and 32 days after the insertion of the device into the water. These signals were also identifiable after 75 minutes and 8 days at a point far from the insertion place. Coumarin 7 was the best marker for the homeopathic complex (FPU) used to treat the wild animals living in the park. The microplates/enzyme-linked immunosorbent assay reader method and the application of a magnetic field to samples were shown to be effective in tracing homeopathic signals by changes in dye absorbance (p ≤ 0.02) in a real-life situation, with large volumes of water, involving many environmental variables, and over large distances.

FLIM nanoscopy resolves the structure and preferential adsorption in the co-nonsolvency of PNIPAM microgels in methanol-water

Polymer microgels are swollen macromolecular networks with a typical size of hundred of nanometers to several microns that show an extraordinary open and responsive architecture to different external stimuli, being therefore important candidates for nanobiotechnology and nanomedical applications such as biocatalysis, sensing and drug delivery. It is therefore crucial to understand the delicate balance of physical-chemical interactions between the polymer backbone and solvent molecules that to a high extent determine their responsivity.In particular, the co-nonsolvency effect of poly(N-isopropylacrylamide) in aqueous alcohols is highly discussed, and there is a disagreement between molecular dynamics (MD) simulations (from literature) of the preferential adsorption of alcohol on the polymer chains and the values obtained by several empirical methods that mostly probe the bulk solvent properties.It is our contention that the most efficacious method for addressing this problem requires a nanoscopic method that can be combined with spectroscopy and record fluorescence spectra and super-resolved fluorescence lifetime images of microgels labeled covalently with the solvatochromic dye Nile Red. By employing this approach, we could simultaneously resolve the structure of sub-micron size objects in the swollen and in the collapsed state and estimate the solvent composition inside of them in ▪–▪ mixtures for two very different polymer architectures. We found an outstanding agreement between the MD simulations and our results that estimate a co-solvent molar fraction excess of approximately 3 with a very flat profile in the lateral direction of the microgel.

Preparation and characterization of novel polyols-based DESs and their use in efficient sequestration of radioactive iodine

The utilization of Novel DESs can be greener alternative to traditional organic solvents. In present study, four polyols-based DESs are synthesized and characterized by several techniques. The prepared DESs are used for the efficient capture of hazardous iodine. In present study by simple combination of two readily accessible, economical, and biodegradable components four polyols-based DESs have been prepared. For the creation of these DESs, a hydrogen bond donors (HBDs) (polyols) and hydrogen bond acceptors (HBAs) (BTEAC) are used, which havemelting points far lower than their respective melting points. The developed DESs were investigated for their physicochemical properties such as density, dynamic viscosity. Our results revealed distinct trends in these properties across different DES compositions, highlighting unique molecular interactions and solvation capabilities. The FTIR and NMR characterization study indicated considerable intermolecular interaction between the various component of the DES system. Further, Kamlet-Taft solvatochromic parameters were determined using Nile red dye, and other solvatochromic dyes. For synthesized DESs, the solvatochromic parameters ENT, normalized polarity parameter, π*, polarity / polarizability; β, hydrogen-bond acceptor basicity and α, hydrogen-bond donor acidity, have been determined. The ENT parameters demonstrate that both non-specific and specific interactions play a significant role in solute–solvent interactions. The synthesized DESs have been utilized for the efficient capture of the iodine. The removal efficiency of DES depends upon the mass of the DESs taken and time duration. These findings deepen our understanding of DES behavior and underscore their versatility in diverse industrial and scientific applications.

ESIPT+TICT-Based Near-IR Detection of Al3+ and F- in Live Cells: Molecular Docking with Acetylcholinesterase.

The interplay of ESIPT+TICT mechanisms in 1,8-naphthalimide-hydroxyquinoline (NQ-OH) molecular rotor were reported for the near-IR 'turn-on' emission (λmax 600 nm) and ratiometric (A405nm/A345nm) absorbance-based detection of Al3+ ions in aqueous medium and live cells which were supported by NMR, IR and CV techniques. The limit of detection (LOD) for Al3+ ions is 100 nM and 14.57 nM. The self-assembled spherical aggregates of NQ-OH transformed into cuboidal aggregates upon coordination with Al3+ ions supported by microscopic and dynamic light scattering (DLS) techniques. The complex NQ-OH+Al3+ was further used for the secondary detection of F- ions in aqueous medium via displacement approach with LOD as low as 2.67 nM. A deeper study revealed that the NQ-OH is a solvatochromic dye. Probably, the NQ-OH either in the aggregated state or in the coordination state with Al3+ ions, showed an increase in the emission intensity at 600 nm due to inhibition of the ESIPT process and trigger of the TICT process. We have demonstrated the utility of NQ-OH for the detection of Al3+ ions and NQ-OH+Al3+ complex for the detection of F- ions in MCF7 live cells. We have also discussed the molecular docking studies of NQ-OH with acetylcholinesterase enzyme.

Reproducing the Solvatochromism of Merocyanines by PCM Calculations.

Polarizable continuum methods (PCM) have been widely employed for simulating solvent effects, in spite of the fact that they either ignore specific interactions in solution or only partially reproduce non-specific contributions. Examples of three solvatochromic dyes with a negative, a positive and a reverse behavior illustrate the achievements and shortcomings of PCM calculations and the causes for their variable success. Even when qualitatively mimicking non-specific solvent effects, departures of calculated values from experimental data may be significant (20-30%). In addition, they can utterly fail to reproduce an inverted behavior that is caused by significant specific contributions by the solvent. As shown through a theoretical model that rationalizes and predicts the solvatochromism of phenolate merocyanines based on DFT (Density Functional Theory) descriptors in the gas phase, PCM shortcomings are to be held responsible for its eventual failure to reproduce experimental data in solution.

The Solvatomagnetism of ET(33) Betaine and of Its Phenolic Precursor.

The 1H and 13C NMR spectra of the N-(3,5-dichloro-4-hydroxyphenyl)- 2,4,6-triphenylpyridinium perchlorate and of its deprotonated betaine 4-(2,4,6-triphenylpyridinio)-2,6-dichlorophenolate (Wolfbeis's ET(33) dye) were recorded in various solvents and analyzed in search of solvent-dependent shifts that characterize their solvatomagnetism, which was compared with the well-known UV-vis spectral behavior of this important solvatochromic dye. Although the NMR spectra of ET(33) and its phenolic precursor in different solvents correlated only poorly with their UV-vis spectral responses, they provided valuable information on specific structural features and solute-solvent interactions that are not available from their UV-vis spectra.

Organelle-Targeted Laurdans Measure Heterogeneity in Subcellular Membranes and Their Responses to Saturated Lipid Stress.

Organelles feature characteristic lipid compositions that lead to differences in membrane properties. In cells, membrane ordering and fluidity are commonly measured using the solvatochromic dye Laurdan, whose fluorescence is sensitive to lipid packing. As a general lipophilic dye, Laurdan stains all hydrophobic environments in cells; therefore, it is challenging to characterize membrane properties in specific organelles or assess their responses to pharmacological treatments in intact cells. Here, we describe the synthesis and application of Laurdan-derived probes that read out the membrane packing of individual cellular organelles. The set of organelle-targeted Laurdans (OTL) localizes to the ER, mitochondria, lysosomes, and Golgi compartments with high specificity while retaining the spectral resolution needed to detect biological changes in membrane ordering. We show that ratiometric imaging with OTLs can resolve membrane heterogeneity within organelles as well as changes in lipid packing resulting from inhibition of trafficking or bioenergetic processes. We apply these probes to characterize organelle-specific responses to saturated lipid stress. While the ER and lysosomal membrane fluidity is sensitive to exogenous saturated fatty acids, that of mitochondrial membranes is protected. We then use differences in ER membrane fluidity to sort populations of cells based on their fatty acid diet, highlighting the ability of organelle-localized solvatochromic probes to distinguish between cells based on their metabolic state. These results expand the repertoire of targeted membrane probes and demonstrate their application in interrogating lipid dysregulation.

Push-Pull Fluorescent Dyes with Trifluoroacetyl Acceptor for High-Fidelity Sensing of Polarity and Heterogeneity of Lipid Droplets.

Imaging and sensing of lipid droplets (LDs) attracted significant attention due to growing evidence for their important role in cell life. Solvatochromic dyes are promising tools to probe LDs' local polarity, but this analysis is biased by their non-negligible emission from intracellular membranes and capacity to emit from both the apolar core and polar interface of LDs. Here, we developed two push-pull solvatochromic dyes based on naphthalene and fluorene cores bearing an exceptionally strong electron acceptor, the trifluoroacetyl group. The latter was found to boost the optical properties of the dyes by shifting their absorption and emission to red and increasing their extinction coefficient, photostability, and sensitivity to solvent polarity (solvatochromism). In contrast to classical solvatochromic dyes, such as parent aldehydes and reference Nile Red, the new dyes exhibited strong fluorescence quenching by millimolar water concentrations in organic solvents. In live cells, the trifluoroacetyl dyes exhibited high specificity to LDs, whereas the parent aldehydes and Nile Red showed a detectable backgrounds from intracellular membranes. Experiments in model lipid membranes and nanoemulsion droplets confirmed the high selectivity of new probes to LDs in contrast to classical solvatochromic dyes. Moreover, the new probes were found to be selective to the LDs oil core, where they can sense lipid unsaturation and chain length. Their ratiometric imaging in cells revealed strong heterogeneity in polarity within LDs, which covered the range of polarities of unsaturated triglyceride oils, whereas Nile Red failed to properly estimate the local polarity of LDs. Finally, the probes revealed that LDs core polarity can be altered by fatty acid diets, which correlates with their chain length and unsaturation.

D-π-A type fluorescent dyes: Effect of π-bridge units on optical and G4 DNA binding properties

Fluorescent solvatochromic dyes that are sensitive to the nature of local microenvironmental, have been explored as probes in applications ranging from the imaging biomolecules to understanding of basic biomolecule functions. To expand the scope of fluorescent solvatochromic dyes for G-quadruplex (G4) DNA structures, and to illustrate the relationship between structure and properties, three newly designed D-π-A type fluorescent dyes were synthesized by introducing diarylimidazole to carbazole skeleton linked to benzene, furan or thiophene π-conjugated bridge and connected with pyridinium acceptor, respectively. Their structural characteristics, optical properties, and G4 DNA binding properties were discussed in detail. In general, the incorporation of furan and thiophene as π-conjugated bridges leads the better conjugation and molecular coplanarity with more efficient intramolecular charge transfer (ICT) effect compared with benzene bridge. The fluorescence intensities induced upon interaction were found that TP-6 with thiophene π-conjugated bridge had the strongest response toward G4 DNAs. In addition, the application of this dye as a fluorescent agent for living cell imaging was also demonstrated.

Microwave-Assisted Synthesis of Solvatochromic Dye and Analysis of Solvent Polarity in Undergraduate Organic Chemistry Laboratory

Microwave-Assisted Synthesis of Solvatochromic Dye and Analysis of Solvent Polarity in Undergraduate Organic Chemistry Laboratory

The Simulation of Solvent Polarizabilities and Dipolarities with Polarizable Continuum Model.

The ability of polarizable continuum models (PCM) to simulate nonspecific solvent effects (dipolarity and polarizability) was evaluated by calculating the transition energies of 1,1,10,10-tetrabutyldecanonaene (ttbp9) and 2-N,N-dimethylamino-7-nitrofluorene (DMANF), basis of Catalán's polarizability (SP) and dipolarity (SdP) solvent scales, respectively. Time-dependent density-functional theory (TD-DFT) calculations were performed at different levels of theory, employing four basis sets in 10 different solvents, covering the full range of the normalized SP and SdP scales. Transition energies were calculated using linear response (LR) and corrected linear response (cLR2) schemes. Although these methods yielded variable mean absolute errors, the LR-PCM calculations reproduced medium polarizability and dipolarity trends. While calculated ttbp9 transition energies correlated with SP and Laurence's dispersion-induced (DI) scales, the DMANF transition energies correlated poorly with SdP or Laurence's ES dipolarity scales. This result agrees with the fact that DMANF solvatochromism is "contaminated" by solvent polarizability and HB acidity. The incorporation of SP or DI contributions led to much better (r2 > 0.95) correlations with the DMANF-calculated transitions. The results offer a clearer picture of the limitations of continuum models in simulating the behavior of solvatochromic dyes in solution by pointing out their poor performance when specific solvent effects, such as hydrogen-bond interactions, play a significant role in their solvatochromism.

Brightness-constant solvatochromic dye for ratiometric fluorescent imaging of lipid dynamics in developing zebrafish

Lipids play a crucial role in the growth and development of organisms. However, the lack of effective chemical tools for lipid imaging has hindered a comprehensive understanding of the dynamic changes in lipid content and types in organisms. Here, we introduce a brightness-constant, lipid droplet-targeting ratiometric fluorescent probe called PAA for visualizing dynamic lipid changes during zebrafish growth and development. PAA was an ultra-stable dimer composed of two carbonylpyrenes. Despite variations in polarity, its absorption spectra, quantum yield and fluorescence brightness remained consistent. However, only fluorescence emission wavelength underwent redshift with increasing polarity. These properties enabled stable lipid imaging throughout the entire live zebrafish and allowed for the identification of lipid polarity using ratiometric fluorescence. Furthermore, PAA revealed changes of lipid composition in developing zebrafish. From 3–5 days post fertilization (dpf), zebrafish with undeveloped digestive organs exhibited a gradual decrease in overall lipid content and a reduction in lipid polarity. Subsequently, as the digestive organs fully developed (6–8 dpf), zebrafish were fed with paramecium, resulting in a gradual increase in overall lipid content and lipid polarity. Moreover, starvation experiments indicated that overall lipid content and polar lipids increased in zebrafish fed with paramecium. The successful application of PAA in visualizing lipid dynamics in zebrafish provides new avenues for studying lipid physiology and pathophysiology in living systems.

Multimodal Phasor Approach to study breast cancer cells invasion in 3D spheroid model.

We implemented a multimodal set of functional imaging techniques optimized for deep-tissue imaging to investigate how cancer cells invade surrounding tissues and how their physiological properties change in the process. As a model for cancer invasion of the extracellular matrix, we created 3D spheroids from triple-negative breast cancer cells (MDA-MB-231) and non-tumorigenic breast epithelial cells (MCF-10A). We analyzed multiple hallmarks of cancer within the same spheroid by combining a number of imaging techniques, such as metabolic imaging of NADH by Fluorescence Lifetime Imaging Microscopy (NADH-FLIM), hyperspectral imaging of a solvatochromic lipophilic dye (Nile Red) and extracellular matrix imaging by Second Harmonic Generation (SHG). We included phasor-based bioimage analysis of spheroids at three different time points, tracking both morphological and biological properties, including cellular metabolism, fatty acids storage, and collagen organization. Employing this multimodal deep-imaging framework, we observed and quantified cancer cell plasticity in response to changes in the environment composition.

Environmental Homeopathy: Homeopathic Potencies Regulate the Growth and Toxicity of Raphidiopsis raciborskii (cyanobacteria) and Can be Tracked Physico-Chemically. Part 2: Physico-chemical Results.

The control of cyanobacterial toxicity and growth by homeopathic potencies was described in Part 1 of this two-part report. Here, a parallel approach characterized the physico-chemical features of the potencies used and the liquid media treated with them, correlating these results with their respective biological effects. Our objective was to establish if physico-chemical parameters can track homeopathic potencies in seawater or artificial seawater medium (ASM)-1 and to discover whether these parameters correlate with previously described biological effects. Artemia franciscana (brine shrimp) cysts were cultivated in seawater challenged with Raphidiopsis raciborskii extract and treated with different homeopathic potencies chosen from a screening process. Cultures of R. raciborskii maintained in ASM-1 were also treated with previously screened homeopathic potencies, and their growth was monitored as a function of time. The physico-chemical properties of the treated media (seawater or ASM-1) were evaluated by their interaction with solvatochromic dyes and changes in pH, conductivity and temperature. Coumarin 7 was found to be a marker for Nitric acidum 6cH and Isotherapic (R. raciborskii extract) 200cH in seawater (analysis of variance [ANOVA], p = 0.0015). Nile red was found to be a marker for Nitric acidum 200cH and Mercurius solubilis 30cH in ASM-1 (ANOVA, p ≤ 0.001). An increase in pH of ASM-1 and endothermic effects were observed after these treatments (two-way ANOVA, p = 0.0001). Seawater and ASM-1 to which potencies had been added were also subjected to a constant unidirectional 2,400 Gauss static magnetic field and found to have enhanced effects on the solvatochromic dyes tested. Homeopathic potencies were specifically traceable in aqueous media using solvatochromic dyes, especially when the samples were subjected to a magnetic field. Results from monitoring other physical parameters, such as pH and temperature, were less specific in relation to potency tracking. However, potency-induced endothermic effects might provide valuable thermodynamic data relating to the nature of potencies.

Fluorescence lifetime imaging microscopy of flexible and rigid dyes probes the biophysical properties of synthetic and biological membranes

Sensing of the biophysical properties of membranes using molecular reporters has recently regained widespread attention. This was elicited by the development of new probes of exquisite optical properties and increased performance, combined with developments in fluorescence detection. Here, we report on fluorescence lifetime imaging of various rigid and flexible fluorescent dyes to probe the biophysical properties of synthetic and biological membranes at steady state as well as upon the action of external membrane-modifying agents. We tested the solvatochromic dyes Nile red and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) (ammonium salt) (NBD), the viscosity sensor Bodipy C12, the flipper dye FliptR, as well as the dyes 3,3′-dioctadecyloxacarbocyanine perchlorate (DiO), Bodipy C16, lissamine-rhodamine, and Atto647, which are dyes with no previous reported environmental sensitivity. The performance of the fluorescent probes, many of which are commercially available, was benchmarked with well-known environmental reporters, with Nile red and Bodipy C12 being specific reporters of medium hydration and viscosity, respectively. We show that some widely used ordinary dyes with no previous report of sensing capabilities can exhibit competing performance compared to highly sensitive commercially available or custom-based solvatochromic dyes, molecular rotors, or flipper in a wide range of biophysics experiments. Compared to other methods, fluorescence lifetime imaging is a minimally invasive and nondestructive method with optical resolution. It enables biophysical mapping at steady state or assessment of the changes induced by membrane-active molecules at subcellular level in both synthetic and biological membranes when intensity measurements fail to do so. The results have important consequences for the specific choice of the sensor and take into consideration factors such as probe sensitivity, response to environmental changes, ease and speed of data analysis, and the probe’s intracellular distribution, as well as potential side effects induced by labeling and imaging.

Extended Reichardt's Dye-Synthesis and Solvatochromic Properties.

Three new pyridinium-phenolate dyes based on the benchmark solvatochromic dye Betaine 30 were synthesised. The dyes contained phenylene spacers between the donor and acceptor groups. Their UV-Vis absorption spectra were measured, with the dyes showing strong negative solvatochromic behaviour comparable to that of Betaine 30. These results stood in contrast to the behaviour of the π-extended dye Betaine 21, originally reported in 1963. This dye was synthesised and found to be significantly more solvatochromic than previously reported but prone to degrade. All π-extended dyes synthesised were found to be unstable in certain solvents. Although the increased distance between donor and acceptor did not enhance solvatochromism to the extent predicted, it was still determined that the reduced planarity caused by a phenylene spacer is not as detrimental as believed.

Conventional and Green Rubber Plasticizers Classified through Nile Red [E(NR)] and Reichardt’s Polarity Scale [ET(30)

After a survey on polymer plasticization theories and conventional criteria to evaluate polymer–plasticizer compatibility through the solubility parameter, an attempt to create a polymer–plasticizer polarity scale through solvatochromic dyes has been made. Since Reichardt’s ET(30) dye is insoluble in rubber hydrocarbon polymers like polyisoprene, polybutadiene and styrene–butadiene copolymers and is not useful for the evaluation of the hydrocarbons and ester plasticizers, the Nile Red solvatochromic dye was instead used extensively and successfully for this class of compounds. A total of 53 different compounds were evaluated with the Nile Red dye and wherever possible also with Reichardt’s ET(33) dye. A very good correlation was then found between the Nile Red scale E(NR) and Reichardt’s ET(30) scale for this class of compounds focusing on diene rubbers and their typical hydrocarbons and new ester plasticizers. Furthermore, the E(NR) scale also shows a reasonable correlation with the total solubility parameter calculated according to the Van Krevelen method. Based on the above results, some conclusion was made about the compatibility between the diene rubbers and the conventional plasticizers, as well as a new and green plasticizer proposed for the rubber compounds.

Disaggregation-driven far-red BODPIY dye for selective G4 DNA structures detection

Push-pull solvatochromic dyes undergoing intramolecular charge transfer (ICT) have emerged as useful tools for imaging target biomolecules directly in living cells and monitoring interactions of biomolecules by changing the signal of their fluorescence. However, the currently reported solvatochromic fluorescent dyes frequently suffer from the problem of inherit background noise, and cause unspecific fluorescence that masks the specific signal from biomolecules. Herein, based on the combined the effect of aggregation-caused quenching (ACQ), a D-π-A structural far-red BODIPY dye BSK was designed and developed as a G-quadruplex (G4) DNA structures probe. In organic solvents, the spectra results underlined the excellent characteristics of BSK, such as high polarity sensitivity and strong solvatochromic effect due to the electron donor–acceptor system. In aqueous solution, BSK underwent aggregation to form nonfluorescent amorphous aggregates in which the dye kept low background fluorescence in a solution. Upon binding of BSK with c-MYC G4 DNA, an intense fluorescence was trigged by the synergistic properties of disaggregation-induced emission and inhibited twisted intramolecular charge transfer, with a low detection limit of 16 nM. In addition, BSK exhibited a selective ability to target G4 DNA structures and effectively differentiated from duplex and single-strand DNAs. Moreover, BSK has the potential to be used in visualizing the cellular nucleus in cells.

Optical Investigation of 2-amino-7-isocyanofluorene, a Novel Blue-Emitting Solvatochromic Dye

Smart solvatochromic isocyano-aminoarenes (ICAArs) have been gaining attention owing to their unique photophysical, antifungal and anticancer properties. Using a simple dehydration reaction with in situ-generated dichlorocarbene, we prepared 2-amino-7-isocyanofluorene (2,7-ICAF). We studied the effect of the longer polarization axis provided by the fluorene core on the spectral properties and we also compared it to those of the starting diamine. 2,7-ICAF shows a clear solvatochromic behavior close to the blue part (370–420 nm) of the visible spectrum. Quantum chemical calculations show internal charge transfer (ICT) between the donor amino and the electron-withdrawing isocyano groups. 2,7-ICAF has high molar absorptivity (ε = 15–18·103 M−1cm−1) and excellent quantum yield (Φf = 70–95%) in most solvents; however, its fluorescence is completely quenched in water. The high brightness (ε·Φf) and close to zero quantum yield in water may be favorable in biolabeling applications, where background fluorescence should be kept minimal. Overall, 2,7-ICAF shows enhanced photophysical properties compared to its previously investigated relative 4-amino-4′-isocyano-1,1′-biphenyl (4,4′-ICAB).