•Novel fluorescent 6-(4-dialkylamino)phenyl-2-pyridones were synthesized by a one-pot method.•All the compounds showed positive solvatofluorochromism.•Intense fluorescence was observed in polar and nonpolar solvents.•The sulfonyl group disturbed the molecular planarity, resulting in intense fluorescence in polar solvents.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.

•Pyridine–pyridone fluorescent sensors exhibited a bathochromic shift with Zn2+.•The length of the methylene spacer influenced the fluorescent properties with Zn2+.•Compound 2 could be applied in the detection of Zn2+ within living cells.Novel, low-molecular-weight fluorescent sensors based on a pyridine–pyridone core structure, which functions as both the chelating part moiety for Zn2+ 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 Zn2+ binding. 5-Benzyl-4-(methylsulfanyl)-[2,2′-bipyridin]-6(1H)-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 Zn2+. In addition, fluorescence microscopy imaging showed that 2 could be used to detect Zn2+ in living cells.