Highly crystalline and fluorescent BODIPY-labelled phenyl-triazole-coumarins as n-type semiconducting materials for OFET devices

In this work, the synthesis of BODIPY-phenyl-triazole labelled coumarins (BPhTCs) using a two-step approach is described. The influence of the BODIPY appending on the photophysical, electrochemical and thermal properties of the phenyl-triazole-coumarin precursors (PhTCs) was investigated. Band gap energies were measured by absorption spectroscopy (2.20 ± 0.02 eV in the solid and 2.35 ± 0.01 eV in solution) and cyclic voltammetry (2.10 ± 0.05 eV). The results are supported by DFT calculations confirming the presence of lowest LUMO levels that facilitate the electron injection and stabilize the electron transport. Their charge-transport parameters were measured in Organic Field-Effect Transistor (OFET) devices. BPhTCs showed an ambipolar transistor behavior with good n-type charge mobilities (10-2 cm2V-1s-1) allowing these derivatives to be employed as promising semiconducting crystalline and fluorescent materials with good thermal and air stability up to 250 °C.

Solvatochromic Sensitivity of BODIPY Probes: A New Tool for Selecting Fluorophores and Polarity Mapping

This research work is devoted to collecting a high-quality dataset of BODIPYs in a series of 10-30 solvents. In total, 115 individual compounds in 71 solvents are represented by 1698 arrays of the spectral and photophysical properties of the fluorophore. Each dye for a series of solvents is characterized by a calculated value of solvatochromic sensitivity according to a semiempirical approach applied to a series of solvents. The whole dataset is classified into 6 and 24 clusters of solvatochromic sensitivity, from high negative to high positive solvatochromism. The results of the analysis are visualized by the polarity mapping plots depicting, in terms of wavenumbers, the absorption versus emission, stokes shift versus - (absorption maxima + emission maxima), and quantum yield versus stokes shift. An analysis of the clusters combining several dyes in an individual series of solvents shows that dyes of a high solvatochromic sensitivity demonstrate regular behaviour of the corresponding plots suitable for polarity and viscosity mapping. The fluorophores collected in this study represent a high quality dataset of pattern dyes for analytical and bioanalytical applications. The developed tools could be applied for the analysis of the applicability domain of the fluorescent sensors.

Stability of Dibromo-Dipyrromethene Complexes Coordinated with B, Zn, and Cd in Solutions of Various Acidities

The spectral luminescent properties of dipyrromethenates halogenated with bromine on both ends of the long axis and coordinated using boron fluoride, zinc, or cadmium in neutral ethanol and acidified with hydrochloric acid solutions were studied. The constants of the acid-base equilibrium of the complexes in the proton-donor solvents in the ground and excited states was determined. The mechanisms of complex protonation were discussed, depending on the structure of the compounds. The electronic structures of the neutral and protonated compounds were modeled and analyzed based on the quantum-chemical method. The structures and spectral-luminescence properties were calculated using the SMD model of ethanol solvent using the TD-DFT theory with the B3LYP functional and the composite def2-SVP/def2-TZVP/def2-TZVPP_ECP basis sets, depending on the atomic number of the elements.

Spectral Characterization of Purpurin Dye and Its Application in pH Sensing, Cell Imaging and Apoptosis Detection

Purpurin (1,2,4-trihydroxy-9,10-anthraquinone) is a natural red dye obtained from the red madder plant that is widely used in food and dyeing industries. The present study investigated the characteristics of purpurin and its application as a pH-sensitive probe to detect the pH of solutions and intracellular pH of mammalian and bacterial cells. Purpurin exhibited high pH-sensitive behavior, low analytes interference, high stability with pKa of 4.6 and visible colorimetric change. 1H NMR and FTIR studies indicated protonation of phenolic hydroxyl group under acidic condition with hypsochromic shift in the absorption and fluorescence spectra relative to that of basic condition. Cell culture studies using HeLa cells revealed that purpurin is well tolerated by the cells and the fluorescent imaging result indicated excellent cell permeability with possible use of the dye to detect the pH fluctuations in living cells under various physiological conditions such as apoptosis. Microbiological studies indicated that the dye could be used for visualization of bacteria under acidic condition.

Recent Advances in Small Molecule-Based Intracellular pH Probes

Intracellular pH plays an important role in many biological and pathological processes. Small-molecule based pH probes are found to be the most effective for pH sensing because of ease of preparation, high sensitivity, and quick response. They have many advantages such as small perturbation to the functions of the target, functional adaptability, cellular component-specific localization, etc. The present review highlights the flurry of recent activity in the development of such probes. The probes are categorized based on the type of fluorophore used like quinoline, coumarin, BODIPY, rhodamine, indolium, naphthalimide, etc., and their analytical performance is discussed.

A novel near-infrared colorimetric and fluorescent probe based on a piperidine-substituted aza-BODIPY photosensitizer for detection of extreme acidity

In this paper, a novel near-infrared (NIR) colorimetric and turn-on fluorescent pH probe (denoted as Probe 1) has been designed and synthesized based on piperidine-substituted aza-BODIPY, and its ability for sensing pH under extremely acidic conditions has been studied. The maximum absorption band of Probe 1 locates at 811 nm in the NIR region in CH₂Cl₂ with an intense molar absorption coefficient of the order of 10⁴ M^-1 cm^-1, which is highly important for biological application. An approximately 156 nm red shift was observed in the absorption of the aza-BODIPY dyes from BDP to Probe 1 (from 655 nm to 811 nm). Dramatic pH responsive absorption and fluorescence changes can be observed under extreme acidity, in conjunction with a visible colorimetric change from purple to blue. Therefore, the detection of pH can be visualized through the color change. Probe 1 with a pK_a value of 2.17 could be used in the detection of pH in the range 0.84 to 3.15. Remarkably, this developed fluorescent probe exhibits extraordinary performances including rapid response time, good stability, high specificity and excellent recyclability. This work will provide a new research platform for detecting strong acidity.

Comparative study of the photophysical and crystallographic properties of 4-(9H-pyreno[4,5-d]imidazol-10-yl)phenol and its alkylated derivatives

The photophysical and crystallographic properties of a para-hydroxphenyl-substituted pyrenoimidazole and its decylated analogues were investigated. The fluorescence of these compounds is sensitive to environmental acidity and basicity.

A novel near-infrared fluorescent sensor for zero background nitrite detection via the "covalent-assembly" principle

Different chemical states of nitrogen are present in many freshwater and marine ecosystems, and nitrite ions are one of the most toxic water-soluble nitrogen species. Developing an effective and convenient sensing method to constantly detect the concentration of nitrite has become a wide concern. Here, a novel near-infrared fluorescent probe (AAC) was designed and synthesized via the "covalent assembly" principle, showing excellent selectivity and high sensitivity for nitrite. A new nitrite-quantitative method was established with the help of AAC, and the detection limit of nitrite using the new method was as low as 6.7 nM. AAC was successfully applied for the quantitative detection of nitrite in real-world environmental and food samples (including river water and Chinese sauerkraut), and the detection results were essentially identical to the results obtained from the traditional Griess assay. Moreover, AAC was successfully applied for tracking nitrite in Escherichia coli by fluorescence imaging. Since nitrite can have devastating effects, the method established with AAC allowed us to "see" effectively about the water quality, food quality, etc.

BODIPY- and Porphyrin-Based Sensors for Recognition of Amino Acids and Their Derivatives

Molecular recognition is a specific non-covalent and frequently reversible interaction between two or more systems based on synthetically predefined character of the receptor. This phenomenon has been extensively studied over past few decades, being of particular interest to researchers due to its widespread occurrence in biological systems. In fact, a straightforward inspiration by biological systems present in living matter and based on, e.g., hydrogen bonding is easily noticeable in construction of molecular probes. A separate aspect also incorporated into the molecular recognition relies on the direct interaction between host and guest with a covalent bonding. To date, various artificial systems exhibiting molecular recognition and based on both types of interactions have been reported. Owing to their rich optoelectronic properties, chromophores constitute a broad and powerful class of receptors for a diverse range of substrates. This review focuses on BODIPY and porphyrin chromophores as probes for molecular recognition and chiral discrimination of amino acids and their derivatives.

A coumarin-connected carboxylic indolinium sensor for cyanide detection in absolute aqueous medium and its application in biological cell imaging

Fluorescent sensor has been noticed in detecting system due to its sensitive, selective, operational simplicity and low cost. We designed a coumarin-connected carboxylic indolium sensor molecule that is water-soluble and cytomembrane-permeable. This infrared (IR) emitter is selectively sensitive towards cyanide detection in aqueous media according to CN^- nucleophilic attack on the indole C=N function. Upon the addition of CN^- anion, the color of sensor in water varied from blue to colorless by naked eyes and fluorescence quenching was observed by spectroscopic method. This was because the intramolecular charge transfer (ICT) effect occurred when the fluorescent sensor was added with CN^-. The minimum detection limit of the sensor's fluorescence response to CN^- is 4.44 × 10^-7 mol/L. Furthermore, the cytotoxicity test shows the sensor has lower cytotoxicity, and indicates that this sensor can be utilized for practical detection of trace cyanide in wastewater.

Multi-state amine sensing by electron transfers in a BODIPY probe

Photoinduced electron transfer sets up the BODIPY probe for multi-state amine sensing by single-electron transfer then collisional quenching.

Imaging of lysosomal pH changes with a novel quinoline/benzothiazole probe

A fluorescent pH probe BTVQ for imaging lysosomal pH fluctuations in live cells and extreme acidity in E. coli cells.

A benzimidazole-based highly selective colorimetric and far-red fluorometric pH sensor for intracellular imaging

A turn-on fluorescent probe (E)-4-(2-(1H-benzo[d]imidazol-2-yl)vinyl)-N,N-diphenylaniline (BVD) was facilely synthesized via the ethylene bridging of triphenylamine and benzimidazole.