Synthesis and Fluorescence Properties of Oxazolo[5,4‐<i>b</i>]quinolines: Exploring Structure‐Property Relationships and Design Strategies for Tailored Photophysical Characteristics

Abstract A series of oxazolo[5,4‐ b ]quinoline derivatives were synthesized via a two‐step process involving the reaction of 4‐trifluoroacetylazlactones with various substituted anilines, followed by intramolecular Friedel‐Crafts‐type cyclization and Robinson‐Gabriel oxazole formation. The systematic investigation of the photophysical properties of the synthesized compounds revealed that the position and nature of the substituents on the oxazolo[5,4‐ b ]quinoline core significantly influenced the absorption and emission characteristics. The 6,8‐dimethoxy substitution pattern was found to provide an optimal balance between high fluorescence quantum yield and moderate Stokes shift, whereas the 5,8‐dimethoxy substitution offered a unique combination of large Stokes shift and long wavelength emission. Additionally, the presence of a trifluoromethyl group at the C‐9 position was identified as a crucial structural feature for maintaining strong fluorescence. These structure‐property relationships provide valuable insights for the rational design of novel fluorescent oxazolo[5,4‐ b ]quinoline derivatives with tailored photophysical properties, which could find potential applications in the development of fluorescent probes and organic light‐emitting materials.