Mitochondria-Targeted Luminescent Organotin(IV) Complexes: Synthesis, Photophysical Characterization, and Live Cell Imaging

Five fluorescent ONO donor-based organotin(IV) complexes, [Sn^IV(L^1-5)Ph₂] (1-5), were synthesized by the one-pot reaction method and fully characterized spectroscopically including the single-crystal X-ray diffraction studies of 2-4. Detailed photophysical characterization of all compounds was performed. All the compounds exhibited high luminescent properties with a quantum yield of 17-53%. Additionally, the results of cellular permeability analysis suggest that they are lipophilic and easily absorbed by cells. Confocal microscopy was used to examine the live cell imaging capability of 1-5, and the results show that the compounds are mostly internalized in mitochondria and exhibit negligible cytotoxicity at imaging concentration. Also, 1-5 exhibited high photostability as compared to the commercial dye and can be used in long-term real-time tracking of cell organelles. Also, it is found that the probes (1-5) are highly tolerable during the changes in mitochondrial morphology. Thus, this kind of low-toxic organotin-based fluorescent probe can assist in imaging of mitochondria within living cells and tracking changes in their morphology.

Tailoring C-6-Substituted Coumarin Scaffolds for Novel Photophysical Properties and Stimuli-Responsive Chromism

A judicious strategy was utilized to envision the substantial regio-positional effects of substituents on the photophysical properties of the 2H-chromen-2-one-3-benzothiazole scaffold-based push-pull framework, named 6-X-CUMs. Among them, 6-NEt₂-CUM reveals prominent excited-state intramolecular charge transfer with a large change of dipole moment (Δμ ∼ 18.23 D), hence displaying remarkable emission solvatochromism from the green (536 nm in cyclohexane) to far-red region (714 nm in dimethyl sulfoxide) and a high-temperature sensitivity (-0.23 nm °C^-1). These, together with unique basicity and acido-/vaporchromism upon acidification elucidated by NMR and photospectroscopic studies, show stark contrast to the conventional 7-NEt₂-CUM. The new series of these tailored 6-X-CUMs represents a new dimension in tailoring the photophysical properties for the development of a promising class of multistimuli-responsive materials.

Self-plasticized, lumogallion-based fluorescent optical sensor for the determination of aluminium (III) with ultra-low detection limits

Aluminium-selective ion optical sensor based on covalently attached lumogallion methacrylate was synthesized and investigated in this study. Lumogallion based derivatives were copolymerized with various methacrylate monomers via a simple one step free radical polymerization to produce a "self-plasticized" copolymer. We demonstrate that covalently attached lumogallion moieties provide adequate functionality to the optical film thus achieving a very simple, one component sensing membrane. Fluorescence experiments demonstrated excellent sensitivity towards aluminium (III) ions with the detection limits found at 4.8 × 10^-12 M. Furthermore, proposed sensor displays high selectivity towards aluminium over a number of biologically relevant cations. Moreover, the synthesized copolymer was used for the fabrication of nanoparticles that exhibit strong fluorescence upon contact with aluminium (III) ions. It is anticipated that lumogallion-based copolymers may form the basis for the development of highly sensitive and robust aluminium selective sensors capable of in situ measurements.

A simple turn-on ESIPT and PET-based fluorescent probe for detection of Al3+ in real-water sample

Aluminum is known as the most ubiquitous metal in earth's crust but its excessive exposure will cause damage to environment and health of the organism. Here, a turn-on Schiff base fluorescence probe STH based on excited state intramolecular proton transfer and photoelectron transfer processes for Al³⁺ detection with fast response rate (within minutes), low detection limit (4.26×10^-8M), high selectivity and reasonable pH application range (5.0-8.0) was developed. Fluorescence titration experiments show that probe STH has an excellent linear relationship (R²=0.9694) with Al³⁺ concentration and could be applied to quantitatively recognize Al³⁺ in real-water samples. Based on Job's plot and in situ mass spectra, two STH molecules will complex with Al³⁺ to form 2:1 complexation with oxygen atoms of hydroxyl and carbonyl groups and nitrogen atom of CN bond participating in coordination.

Coumarin-Based Small-Molecule Fluorescent Chemosensors

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

A novel coumarin-based fluorescence chemosensor for Al3+ and its application in cell imaging

As an efficient turn-on fluorescent chemosensor for Al³⁺, a new coumarin derivative (CND) has been designed and synthesized by the condensation of 8-formyl-7-hydroxycoumarin with niacin hydrazide. The spectroscopic studies revealed that the sensor CND exhibited a remarkable fluorescence enhancement towards Al³⁺ with high selectivity and sensitivity in EtOH-HEPES (95:5, v/v, pH = 7.40), which was attributed to the photoinduced electron transfer (PET) and CN isomerization mechanism. Fluorescence titration calculations data showed that the detection limit and the association constants of CND for Al³⁺ were found to be 2.51 × 10^-7 M and 9.64 × 10⁴ M^-1, respectively. The results of experiments, including Job's plot, ¹H NMR titration and ESI-MS, revealed that the stoichiometric binding between CND and Al³⁺ was 1:1. The investigations of the pH dependency of CND for Al³⁺ detection, and the cell imaging suggested the sensor CND could be promisingly applied for the recognition of Al³⁺ in biological cells.

Bis-anthracene derived bis-pyridine: selective fluorescence sensing of Al3+ ions

A novel bis-anthracene molecule linked to bis-pyridine by xylylene dibromide (APC) was synthesized as a potent sensor for the detection of Al³⁺ ions.

A highly selective and sensitive fluorescent chemosensor and its application for rapid on-site detection of Al3

In this paper, a simple naphthalene-based derivative (HL) has been designed and synthesized as a Al³⁺-selective fluorescent chemosensor based on the PET mechanism. HL exhibited high selectivity and sensitivity towards Al³⁺ over other commonly coexisting metal ions in ethanol with a detection limit of 2.72nM. The 1:1 binding stoichiometry of the complex (HL-Al³⁺) was determined from the Job's plot based on fluorescence titrations and the ESI-MS spectrum data. Moreover, the binding site of HL with Al³⁺ was assured by the ¹H NMR titration experiment. The binding constant (Ka) of the complex (HL-Al³⁺) was calculated to be 5.06×10⁴M^-1 according to the Benesi-Hildebrand equation. In addition, the recognizing process of HL towards Al³⁺ was chemically reversible by adding Na₂EDTA. Importantly, HL could directly and rapidly detect aluminum ion through the filter paper without resorting to additional instrumental analysis.

Dihydroindeno[1,2-b]pyrroles: new Al3+selective off–on chemosensors for bio-imaging in living HepG2 cells

An approach for the expeditious synthesis of a new Al³⁺-selective turn-on dihydroindeno[1,2-b]pyrrole probe under environmentally benevolent conditions and its bio-imaging studies on HepG2 cell.

A two-pocket Schiff-base molecule as a chemosensor for Al3+

A new Schiff-base molecule with two binding pockets acts as a selective fluorescent chemosensor for Al³⁺.

Crystal structure of di-aqua-bis-(7-di-ethyl-amino-3-formyl-2-oxo-2H-chromen-4-olato-κ(2) O (3),O (4))zinc(II) dimethyl sulfoxide disolvate

The structure of the title coordination complex, [Zn(C14H14NO4)2(H2O)2]·2C2H6OS, shows that the Zn(II) cation adopts an octa-hedral geometry and lies on an inversion center. Two organic ligands occupy the equatorial positions of the coordination sphere, forming a chelate ring motif via the O atom on the formyl group and another O atom of the carbonyl group (a pseudo-β-diketone motif). Two water mol-ecules occupy the remaining coordination sites of the Zn(II) cation in the axial positions. The water mol-ecules are each hydrogen bonded to a single dimethyl sulfoxide mol-ecule that has been entrapped in the crystal lattice.

Development of a cell permeable red-shifted CHEF-based chemosensor for Al(3+) ion by controlling PET

A structurally modified quinazoline derivative (L) acts as highly selective chemosensor for Al(3+) ions in DMSO-H2O (1:9, v/v) over the other competitive metal ions. L shows a red shifted fluorescence after the addition of Al(3+) ions and later the further fluorescence enhancement is due to chelation enhanced fluorescence (CHEF) through inhibition of photoinduced electron transfer (PET). This probe (L) detects Al(3+) ions as low as 9nM in DMSO-H2O (1:9, v/v) at biological pH. The non-cytotoxic probe (L) can efficiently detect the intercellular distribution of Al(3+) ions in living cells under a fluorescence microscope to exhibit its sensible applications in the biological systems.

Recognition of Mg²⁺ by a new fluorescent "turn-on" chemosensor based on pyridyl-hydrazono-coumarin

A new fluoroionophore PyHC bearing 2-pyridylhydrazone and 7-hydroxycoumarin moieties for selective detection of Mg(2+) was synthesized and characterized. This chemosensor exhibited "turn-on" fluorescence behavior and was sensitive to Mg(2+) concentrations as low as 105 nmol L(-1) in ethanol-water solution. Detailed spectroscopic studies revealed the binding mode of a 1:1 complex between PyHC and Mg(2+) that leads to a fluorescence enhancement.

Two Schiff-base fluorescent sensors for selective sensing of aluminum (III): Experimental and computational studies

Two Schiff-base fluorescent sensors have been synthesized, which both can act as fluorescent probes for Al(3+), upon addition of Al(3+), they exhibit a large fluorescence enhancement which might be attributed to the formation of 1:1 ligand-Al complexes which inhibit photoinduced electron transfer (PET) progress, and that the proposed binding modes of the sensors and Al(3+) are identified by theoretical calculations.

A highly selective and sensitive fluorescent turn-on Al3+ chemosensor in aqueous media and living cells: experimental and theoretical studies

A highly selective and sensitive fluorescent chemosensor exhibited enhanced fluorescence in the presence of Al³⁺ and in living cells.

2-(Alkylamino)-3-aryl-6,7-dihydrobenzofuran-4(5H)-ones: Improved Synthesis and their Photophysical Properties

Furans are an important class of compounds and exhibit a diverse range of activities and properties. As such, improved synthetic access to furans is an important research goal. In the present report, a solvent- and catalyst-free reaction between 5,5-dimethyl-1,3-cyclohexanedione (dimedone), an aryl aldehyde and an isocyanide under microwave irradiation is presented. This method is significantly improved from previously described protocols in terms of applicability of wide ranging aryl aldehydes, better yields, shorter reaction times, facile work up and essentially no need of column chromatography. The photophysical properties of this series of compounds were studied for their possible applicability in the field of metal ion sensors. In solution, two compounds, 2-(cyclohexylamino)-3-(1H-indol-3-yl)-6,6-dimethyl-6,7-dihydrobenzofuran-4(5H)-one (1 i) and 2-(tert-butylamino)-3-(1H-indol-3-yl)-6,6-dimethyl-6,7-dihydrobenzofuran-4(5H)-one (1 j), underwent an observable color change from yellow to colorless in the presence of aluminum(III) ions. Further studies to investigate the UV absorption and luminescence behavior of these compounds revealed their utility as "naked-eye sensors" for aluminum detection.

A highly selective turn-on fluorescent probe for Al(III) based on coumarin and its application in vivo

In this study, a turn-on coumarin-based fluorescent probe, 7-hydroxy-6-[(2-hydroxy-naphthalen-1-ylmethylene)-amino]-4-methyl-chroman-2-one (CN), was developed for detecting Al(3+) in aqueous systems. The binding ratio of CN-Al(3+) complexes was determined from the Job plot and ESI-MS data to be 1 : 1. The binding constant (Ka) of Al(3+) binding to CN was calculated to be 9.55 × 10(4) M(-1) from a Benesi-Hildebrand plot and the detection limit was evaluated to be as low as 0.10 μM (LOD = 3σ/slope). CN could be used as an effective fluorescent probe for detecting Al(3+) in living HeLa cells. Moreover, CN could also be applied in the in vivo detection of Al(3+) in zebrafish.

A new fluorescent probe for Al(3+) based on rhodamine 6G and its application to bioimaging

A water-soluble rhodamine-based derivative (L) has been rationally designed for selective recognition of Al(3+) in aqueous medium with good sensitivity. The addition of Al(3+) to the aqueous solution of L induces a remarkable fluorescence enhancement along with obvious color change detected by the naked eye, due to the ring-opening mechanism of the rhodamine spirolactam, which has been proved by single crystal diffraction analyses directly. The recognizing behavior has been investigated both experimentally and computationally. Furthermore, the fluorescent probe can also be used as a bioimaging reagent for detection of Al(3+) in living cells.

A polynuclear hetero atom containing molecular organic scaffold to detect Al3+ ion through a fluorescence turn-on response

A simple polynuclear hetero atom (N and O) containing molecular organic scaffold/probe, 3 has been designed and synthesized and explored as a potential chemosensor to detect Al³⁺ (22 nM; ∼0.6 ppb) ion in a HEPES buffer.

Zn2+mediated solvent free solid state red emitting fluorescent complex formation in a mortar–pestle along with living cell imaging studies

AAScan selectively detect Zn²⁺fluorometrically and colorimetrically in the presence of common cations and anions in a solvent free method.

A Highly Selective and Sensitive Chemosensor for Colorimetric and Fluorescent Detection of Al3+ and Living Cell Imaging

A colorimetric and fluorescent dual chemosensor for detecting Al3+, (E)-N′-((2-hydroxynaphthalen-1-yl)methylene)nicotinohydrazide (HNN), was developed by combining 2-hydroxy-1-naphthaldehyde with nicotinohydrazide. Addition of Al3+ to EtOH–H2O solution of HNN gives rise to a visible colour change from colourless to light blue and a significantly enhanced fluorescence. Other metal ions including Na+, K+, Ca2+, Mg2+, Mn2+, Co2+, Ni2+, Cu2+, Cr3+, Ag+, Pb2+, Zn2+, Cd2+, Hg2+, Fe2+, and Fe3+ have no or little effect on the specific response of HNN to Al3+. The binding mode of HNN–Al3+ complex was further clarified by electrospray ionisation mass spectrometry and 1H NMR titration experiments.

Aminomethylpyrene-based imino-phenols as primary fluorescence switch-on sensors for Al3+ in solution and in Vero cells and their complexes as secondary recognition ensembles toward pyrophosphate

Three aminomethylpyrene-based salicyl-imines, viz.L1, L2 and L3 were designed and synthesized for Al³⁺ ion sensing.

A novel turn-on Schiff-base fluorescent sensor for aluminum(iii) ions in living cells

Quinoline Schiff base L exhibits a more than 38-fold fluorescence enhancement after addition of Al³⁺ ions at an excitation wavelength of 373 nm, and shows a high selectivity for Al³⁺ over other metal ions.

A simple and dual responsive efficient new Schiff base chemoreceptor for selective sensing of F− and Hg2+: application to bioimaging in living cells and mimicking of molecular logic gates

A novel colorimetric hydrazine-functionalized Schiff base chemoreceptor, NPMP, was synthesized following a simple one-step Schiff base condensation pathway.

Fluorescent sensor for selective detection of Al(3+) based on quinoline-coumarin conjugate

A fluorescence probe, 8-formyl-7-hydroxyl-4-methyl coumarin - (2'-methylquinoline-4-formyl) hydrazone (L) has been synthesized. The chemosensor is found preferential binding to Al(3+) in presence of other competitive ions with associated changes in its optical and fluorescence spectra behavior. Upon addition of Al(3+) to a solution of L, it shows 200-fold enhancement of fluorescence intensity which might be attributed to form a 2:1 stoichiometry of the binding mode of LAl(III) and the chelation enhanced fluorescence (CHEF) process at 479nm in ethanol. The lowest detection limit for Al(3+) is determined as 8.2×10(-7)M.

A quinoline derivative as an efficient sensor to detect selectively Al³⁺ ion

A quinoline-based Schiff base 1 has been utilized as a fluorescence chemosensor for the selective detection of Al(3+). The receptor 1 exhibited a high association constant (3.67 × 10(5) M(-1)) with submicromolar detection limit (0.18 ppm) towards Al(3+) in CH3CN solution.

Al3+ selective coumarin based reversible chemosensor: application in living cell imaging and as integrated molecular logic gate

The new coumarin based fluorescent ‘turn-on’ chemosensor (H₂L) efficiently detects Al³⁺ over other metal ions. It is efficient in detecting Al³⁺ in the intracellular region of HeLa cells and also exhibits an INHIBIT logic gate with Al³⁺ and EDTA as chemical inputs.