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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: 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]

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]

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]