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Novel, low-molecular-weight fluorescent sensors based on a pyridine–pyridone core structure, which functions as both the chelating part moiety for Zn 2+ and as the fluorophore, were investigated. The length of the methylene spacer between the phenyl ring and the 3-position of the pyridone ring greatly influenced the emission wavelength and intensity upon Zn 2+ binding. 5-Benzyl-4-(methylsulfanyl)-[2,2′-bipyridin]-6(1 H )-one ( 2 ) (MW = 308) with a methylene spacer of n = 1 showed good water solubility, a 30 nm bathochromic shift in its emission wavelength and an 18-fold fluorescence enhancement in response to Zn 2+ . In addition, fluorescence microscopy imaging showed that 2 could be used to detect Zn 2+ in living cells. [ABSTRACT FROM AUTHOR]

Abstract: One-pot synthesis of a new 2-pyrone dye (3a) by the reaction of 4-diethylamino-acetophenone (1) with methyl 2-cyano-3,3-bis(methylsulfanyl)acrylate (2) in the presence of sodium hydroxide as the base was carried out in DMSO. Compound 4a was synthesized by the replacement of methylsulfanyl group of 3a with dimethylamine at 4-position of pyrone ring. Similarly, compound 5a was prepared via the reaction of 3a with diethyl malonate. Compounds 3a–5a exhibited the following fluorescence in the solid state: red (3a), green (4a), and orange (5a). In addition, it was revealed that 2-pyrone dyes exhibit fluorescence in various solvents and show positive solvatochromism. Compounds 3a and 5a exhibited intense fluorescence in chloroform and dichloromethane (fluorescence quantum yield Φ: 0.94–0.95). In contrast, compound 4a exhibited intense fluorescence in polar solvents (methanol: Φ = 0.92). These 2-pyrone dyes have the potential for applications in various fields. [Copyright &y& Elsevier]

Abstract: The development of a water-soluble and small molecular weight fluorescent probe, 3-(4-methoxyphenyl)-4-(methylsulfanyl)-6-(pyridin-2-yl)pyridin-2(1H)-one (3), for detecting Zn2+ based on pyridine–pyridone skeleton is reported. We observed a clear chelation enhanced fluorescence effect of 3 in the presence of Zn2+. Other fluorescent properties of 3 are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Polysubstituted pyridine derivatives were synthesized by the reaction of ketene dithioacetal, 3,3-bis(methylsulfanyl)methylenemalononitrile 1b, with a variety of active methylene compounds in the presence of either sodium hydroxide or potassium hydroxide as a base in DMSO. This reaction was carried out under economical one-pot reaction conditions (cheap catalyst and solvent) and solved the problem of the odor of methanethiol, commonly derived from reactions of ketene dithioacetals. This is a significant enhancement of GSC (green and sustainable chemistry) in the field of ketene dithioacetal chemistry. [Copyright &y& Elsevier]

A high-affinity and low-molecular-weight fluorescent Zn 2+ sensor 1 based on a 2,2′-bipyridine scaffold, which functions as both the chelating moiety for Zn 2+ and the fluorophore, was developed and evaluated in biological applications. Controlling the occurrence of tautomerism of the chelating moiety for Zn 2+ by introducing an amino group at the 6-position of the pyridine ring dramatically increased the binding affinity toward Zn 2+ . Fluorescent sensor 1 exhibited a nanomolar-range dissociation constant ( K d = 2.2 nM), a large Stokes shift (140 nm), and an 8.6-fold turn-on response to Zn 2+ under physiological conditions. Fluorescence images revealed that fluorescent sensor 1 exhibits good properties with respect to aqueous solubility and cell permeability and can quantitatively detect the Zn 2+ levels in living cells. Furthermore, a 65 Zn 2+ radioactive zinc isotope uptake study revealed the real concentration of accumulated Zn 2+ at the detection limit. The novel fluorescent sensor 1 is a promising sensor for use in biological applications. [ABSTRACT FROM AUTHOR]

Abstract: A combined experimental and computational study was performed for the spectroscopic properties of novel 2(1H)-pyridones. The compounds were found to be virtually non-fluorescence in solution while modestly fluorescent in solid state. The solvent effects on the UV–vis and fluorescence maxima were estimated by means of a series of ab-initio quantum chemical calculations in conjunction with Polarizable Continuum Model (PCM) method. Influence of structural displacements and intermolecular interactions in crystalline state were examined in details on the spectra of two representative compounds by using Fragment Molecular Orbital (FMO) scheme. The FMO pair interaction analysis of the spectra indicate that (1) intermolecular hydrogen bonds provoke bathochromic shifts (2) electrostatic interactions induce hypsochromic shifts (3) crystal packing effects induce hypsochromic shifts in total from the maxima in vacuo. [Copyright &y& Elsevier]

Abstract: We report a novel series of fluorescent Zn2+ sensors based on a pyridine–pyridone core structure, which functions as both the chelating part for Zn2+ and as the fluorophore. Pyridine–pyridone derivatives obtained by replacement of an electron-donating group with an electronic-withdrawing group at the 3-position of the pyridone ring showed almost no background fluorescence because electron transfer to the fluorophore was inhibited. However, these derivatives showed strong fluorescence with Zn2+. Coordination with Zn2+ greatly influenced the electron transfer of the fluorophore, and, as a result, enabled fluorescence ON/OFF switching. In these sensors, 4-[4-(methylsulfanyl)-2-oxo-6-(pyridin-2-yl)-1,2-dihydropyridin-3-yl]benzoic acid (5) displayed excellent properties: small molecular weight (MW=338), good water solubility, large Stokes shift (132nm), and fluorescence ON/OFF switching with Zn2+. In addition, fluorescence images of Zn2+ with 5 in living cells show that the new fluorescent sensor is useful for biological applications. [Copyright &y& Elsevier]

Abstract: The major electronic absorption features in visible region were computationally investigated for a series of novel N-methylmaleimide derivatives. The newly synthesized compounds through the reaction of indolizines with N-methylmaleimides exhibited their maxima ranging 587–634nm in solution at room temperature. Time dependent density functional theory (TD-DFT) calculations were performed in order to elucidate their structure–color relationship, as well as to assess its performance using a variety of exchange-correlation (XC) functionals and basis sets. 4-(Indolizin-3-yl)-1-methyl-2,5-dioxo-1H-pyrrole-3-carbonitrile (referred to 3a hereafter), a representative of the new compounds, was analyzed in detail on its intramolecular push–pull electronic structure. As a consequence of systematic evaluation of computational strategies for 3a, we found that the theoretical λ max obtained by PCM-TD-DFT/6-31+G(d,p)//DFT/6-311G(2d,2p) level of theory, which was consistently employed throughout this study, has converged within 2nm deviation from λ max of the most elaborated level considered. Among some of the molecules with near-planarity structure, unusual discrepancies between the theoretical and the experimental λ max were observed, which should be attributed to the well-known TD-DFT limitation to describe multi-configurational or charge transfer (CT) excitations. [Copyright &y& Elsevier]

Abstract: This article comprehensively describes the condensation reactions of functionalized maleimides (3-methylthio-2,5-dioxo-1H-pyrroles) with some nucleophilic reagents to afford a series of novel heterocycles, as briefly reported in a previous communication [Tominaga Y, Komiya K, Itonaga S, Yoshioka N, Kataoka S, Sasaki K, et al. Heterocycles 1997;46:41]. The reactions of the functionalized maleimides (5a–c) with N,N-dialkylanilines (6a–d) smoothly proceeded to give the corresponding 3-(4-dialkylamino)phenyl-1-methyl-1H-pyrrole-2,5-diones (7a–i). Cyclic products, the 2H,4H-[1]benzopyrano[3,4-c]pyrrole-1,3,4-triones (10a–c, 12, 13) were also obtained within the same reaction framework, using 3-dialkylaminophenols (6g–j) and resorcinol (6k) as the nucleophilic reagents. Further treatments of (7a,b,h) with Lawesson''s reagent afforded the brilliant blue mono-thiocarbonyls, 4-(4-dialkylamino)phenyl-3-cyano-1-methyl-5-oxo-pyrrole-2-thiones (9a–c). The UV/vis spectral characteristics of the new heterocycles, particularly of the controversial aromatic mono-thiocarbonyl compounds (9a–c), were computationally analyzed by means of semi-empirical and Time Dependent Density Functional Theory (TDDFT) quantum chemistry calculations. [Copyright &y& Elsevier]

Two 2-pyridone tautomeric analogs, methoxypyridine 4 and N -methylpyridone 5 , were synthesized, and their spectroscopic properties were investigated both experimentally and computationally. A detailed photophysical study reveals that 4 shows high fluorescence quantum yields not only in chloroform but also in ethanol, and the strong fluorescence in solution might be attributed to the enol form (pyridine) of the 2-pyridone. Furthermore, we designed and synthesized novel 2-substitued pyridines to achieve more intense emissions in both solution and the solid state. Substituent modification with phenylsulfonyl, morpholino, and 4-diethylamino groups greatly affected the fluorescence properties, and methoxypyridine 7 and morpholinopyridine compound 8 showed fluorescence in various solvents (Ф = 0.59–0.95) and the solid state (Ф = 0.12–0.15). A hypsochromic shift in the emission maximum wavelength and strong fluorescence in the solid state (Ф = 0.39) were observed for dimorpholinopyridine 9. Morpholinopyridine 11 showed intense fluorescence in all nonpolar and polar solvents. Systematic time-dependent density functional theory calculations were performed for the compounds whose electronic and fluorescent maxima were computationally reproduced with good agreement to those from experiment. In detail, the drastic difference in the emission intensity between 4 and 5 in solution was successfully explained using CASSCF calculations, which revealed the presence of conical intersections between the ground and the excited states. • Joint experimental and computational studies of new 2-pyridone tautomeric compounds were performed. • Strong fluorescence in solution is attributed to the enol form of the 2-pyridone. • Methoxypyridine and morpholinopyridines exhibited solid-state fluorescence and a high fluorescence quantum yield in solution. • Fluorescence solvatochromic effects depend on the chemical structure and arrangement of the substituents were observed. [ABSTRACT FROM AUTHOR]

Novel highly emissive 2-pyridone-based compounds 3a,b and 4a–d were synthesized by a convenient one-pot method from 4-(dialkylamino)acetophenones ( 1a , b ) and cyanoketene dithioacetal ( 2a ) or sulfonyl ketene dithioacetals ( 2b , c ), and their fluorescence properties were investigated. A simple structure modification of 2-pyridones significantly affected their optical properties including the emission wavelength and fluorescence intensity. All the 6-(4-dialkylamino)phenyl-2-pyridones showed positive solvatofluorochromism and intense blue-green fluorescence in nonpolar solvents such as chloroform ( Ф : 0.80–0.92) and dichloromethane ( Ф : 0.83–0.94). A hypsochromic shift of the fluorescence emission maxima and strong fluorescence in a polar solvent were observed by substituting the dimethylamino group with a diethylamino group. Introduction of a sulfonyl group disturbed the molecular planarity of compounds 4a , 4b , and 4d , resulting in a strong fluorescence in acetone ( Ф : 0.86–0.95) and acetonitrile ( Ф : 0.59–0.88). These results indicate that 2-pyridone-based compounds have great potential as fluorophores for various practical applications. [ABSTRACT FROM AUTHOR]