2-Pyridone-based fluorophores containing 4-dialkylamino-phenyl group: Synthesis and fluorescence properties in solutions and in solid state

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.