Push−Pull Aminobithiophenes — Highly Fluorescent Stable Fluorophores

Ultrasound-Assisted Synthesis of Chalcone: A Highly Sensitive and Selective Fluorescent Chemosensor for the Detection of Fe3+ in Aqueous Media

The chalcone compound DHPO was synthesized through a chemical reaction between 1-(2-hydroxyphenyl)-ethanone and 3,4-dimethoxy benzaldehyde under ultrasound irradiation. The interaction between the DHPO compound and several metal ions was studied using fluorescence behavior, revealing that the chalcone function as a "turn on and turn off" switch fluorescent sensor, for selectively and sensitively detecting Fe3+ ions. The process of fluorescence quenching and complexation of DHPO with Fe3+ ion was further studied using methods such as Benesi-Hildebrand, Stern-Volmer plot, and job plot.

Alkoxy-Substituted Quadrupolar Fluorescent Dyes

Polar and polarizable π-conjugated organic molecules containing push-pull chromophores have been investigated extensively in the past. Identifying unique backbones and building blocks for fluorescent dyes is a timely exercise. Here, we report the synthesis and characterization of a series of fluorescent dyes containing quadrupolar A-D-A constitutions (where A = acceptor and D = donor), which exhibit fluorescence emission at a variety of different wavelengths. We have investigated the effects of different electron-withdrawing groups, located at both termini of a para-terphenylene backbone, by steady-state UV/vis and fluorescence spectroscopy. Pyridine and substituted pyridinium units are also introduced during the construction of the quadrupolar backbones. Depending on the quadrupolarity, fluorescence emission wavelengths cover from 380 to 557 nm. Time-resolved absorption and emission spectroscopy reveal that the photophysical properties of those quadrupolar dyes result from intramolecular charge transfer. One of the dyes we have investigated is a symmetrical box-like tetracationic cyclophane. Its water-soluble tetrachloride, which is non-cytotoxic to cells up to a loading concentration of 1 μM, has been employed in live-cell imaging. When taken up by cells, the tetrachloride emits a green fluorescence emission without any hint of photobleaching or disruption of normal cell behavior. We envision that our design strategy of modifying molecules through the functionalization of the quadrupolar building blocks as chromophores will lead to future generations of fluorescent dyes in which these A-D-A constitutional fragments are incorporated into more complex molecules and polymers for broader photophysical and biological applications.

Synthesis and Spectral Properties of Aggregation-Induced Emission-Active Push-Pull Chromophores Based On Isoindole Scaffolds

A new class of tailor-made push-pull isoindole fluorophores has been synthesized through the combination of Suzuki coupling and Knoevenagel reactions. The efficient synthetic strategy rendered the isoindole scaffold as the π-bridge and the isolation spacer and provided dyes bearing various types of electron donors and electron acceptors for manipulating their energy gaps and tuning their absorptions and emissions. Most of the N-alkylated isoindole dyes showed aggregation-induced emission behaviors suitable for bioimaging and nice solid-state emission with maxima up to 851 nm.

Novel cationic aryl bithiophene/terthiophene derivatives as corrosion inhibitors by chemical, electrochemical and surface investigations

Two novel bithienyl fluorobenzamidine derivatives namely, 4-([2,2′:5′,2′′-terthiophen]-5-yl)-2-fluorobenzamidine hydrochloride salt (MA-1615), 5′-(4-amidino-3-fluorophenyl)-[2,2′-bithiophene]-5-carboxamidine dihydrochloride salt (MA-1740) were synthesized, characterized and their corrosion inhibition properties were evaluated by electrochemical methods for carbon steel (C-steel) in 1 M HCl. Experimental investigations revealed that the inhibition effectiveness of the investigated inhibitors (INHs) by the Tafel polarization method followed the order: MA-1740 (96.9%) > MA-1615 (95.6%), demonstrating higher efficiency than inhibitors of similar structure reported in the literature. The investigated bithiophene derivatives exhibit mixed-type corrosion inhibition characteristics by blocking the active sites on the surface of C-steel. EIS study revealed that the INHs behave as interface-type corrosion inhibitors. UV–Visible spectrometric measurements confirmed a complex formation between the Fe²⁺ cation released during the corrosion reactions and inhibitor molecules.

β-IminoBODIPY oligomers: facilely accessible π-conjugated luminescent BODIPY arrays

A combination of imine-BODIPY chemistry was employed to fabricate luminescent π-conjugated BODIPY oligomers and BODIPY-functionalized silica gel.

Fluorogenic small molecules requiring reaction with a specific protein to create a fluorescent conjugate for biological imaging--what we know and what we need to learn

We seek fluorogenic small molecules that generate a fluorescent conjugate signal if and only if they react with a given protein-of-interest (i.e., small molecules for which noncovalent binding to the protein-of-interest is insufficient to generate fluorescence). Consequently, it is the new chemical entity afforded by the generally irreversible reaction between the small molecule and the protein-of-interest that enables the energy of an electron occupying the lowest unoccupied molecular orbital (LUMO) of the chromophore to be given off as a photon instead of being dissipated by nonradiative mechanisms in complex biological environments. This category of fluorogenic small molecules is created by starting with environmentally sensitive fluorophores that are modified by an essential functional group that efficiently quenches the fluorescence until a chemoselective reaction between that functional group and the protein-of-interest occurs, yielding the fluorescent conjugate. Fluorogenic small molecules are envisioned to be useful for a wide variety of applications, including live cell imaging without the requirement for washing steps and pulse-chase kinetic analyses of protein synthesis, trafficking, degradation, etc.

Sc(OTf)3-mediated 1,3-dipolar cycloaddition-ring cleavage-rearrangement: a highly stereoselective access to Z-β-enaminonitriles

A novel and highly stereoselective synthesis of Z-β-enaminonitriles from azides and α,β-unsaturated nitriles is reported. The reaction proceeds via a 1,3-dipolar cycloaddition-ring cleavage-rearrangement cascade mediated by a catalytic amount of Sc(OTf)3. A plausible reaction mechanism for this process is depicted.

Imides modified benzopicenes: synthesis, solid structure and optoelectronic properties

Imide-modified polycyclic aromatic hydrocarbons can be widely applied in the field of optoelectronic materials.

Solvatochromic investigation of highly fluorescent 2-aminobithiophene derivatives

The solvatochromic and electrochemical properties of electronic push-pull 2-aminobithiophenes consisting of an aldehyde and nitro withdrawing groups were examined. With the use of an integrating sphere, the absolute quantum yields of the bithiophenes were measured. They were found to be highly fluorescent (Φfl > 70%), provided the nitro group was not located in the 4'-position. High fluorescence yields were observed regardless of solvent, except for alcohols, notably methanol and ethanol. Cryofluorescence was used to probe the bithiophene temperature dependent excited state deactivation modes. The singlet excited state deactivation mode other than fluorescence was found to be internal conversion involving rotation around the thiophene-thiophene bond. Deactivation by intersystem crossing to the triplet state occurred in ca. 40% only for the unsubstituted 2-aminobithiophene. In contrast, the fluorescence was quenched by photoinduced intramolecular electron transfer when the nitro group was located in the 4'-position of the bithiophene. Both the absorbance and fluorescence of the bithiophenes were found to be solvatochromic with more pronounced solvent dependent shifts being observed with the fluorescence. In fact, both the fluorescence and Stokes shifts were linearly dependent on the ET(30) solvent parameter. Deviations from the linear trend of the Stokes shift with ET(30) were observed in ethanol and methanol as a result of intermolecular hydrogen abstraction from the solvent and by the excited nitro group. The oxidation potential of the bithiophenes was also highly dependent on the type and number of the electron withdrawing substituents, with values ranging between 0.8 and 1.2 V vs. SCE.

Using Quenching Kinetics and Thermodynamics of Amino-Fluorophores as Empirical Tools for Predicting Boronic Acid Sensors Suitable for Use in Physiological Conditions

A series of water-soluble 1-amino-naphthalenes and 2-amino-fluorenes are prepared. These serve as model fluorophores for measuring the thermodynamics and kinetics of fluorescence quenching with phenylboronic acids and aliphatic amines. Steady-state and time-resolved fluorescence quenching kinetics are investigated using the Stern–Volmer method. Diffusion limited quenching constants and exergonic thermodynamics of electron transfer are derived for the 5-amino-1-napthol and 2-aminofluorene derivatives with phenylboronic acid and/or an aliphatic imine. No quenching and endergonic thermodynamics or electron transfer are observed for 5-sulfonamide, 5-sulfonic acid, or 5-hydroxy-7-sulfonic acid aminonaphthalene derivatives. Boronic acid sensors synthesized from these aminofluorophores by reductive amination with 2-formylphenylboronic acid undergo fluorescence revival in the presence of saccharides only when the fluorophore demonstrates diffusion limited quenching kinetics and exergonic thermodynamics of electron transfer with the boronic acid or imine quenchers. Thus, these two properties are suitable empirical tools for predicting saccharide-induced fluorescence revival of boronic acid sensors.