Synthesis and Photophysical Properties of Push–Pull Type Pyrroloquinolone Fluorescent Dyes

The quinolone scaffold is a key structural motif found in heterocycles exhibiting biological activities, coordination behaviors, and photosensitizing properties. Herein, we report the synthesis and photophysical characterization of Donor−π–Acceptor (D−π–A) systems incorporating the pyrroloquinolone core. By varying the electron-donating and electron-withdrawing substituents, we demonstrate the formation of charge-transfer (CT) fluorophores exhibiting Stokes shifts exceeding 6000 cm –1 and red emission. While the absorption spectra are essentially unaffected by solvent polarity, pronounced positive solvatofluorochromism is observed. Fluorescence quenching is nevertheless noted in polar solvents such as acetone, acetonitrile, and ethanol. The photophysical behavior of the dyes is further rationalized through time-dependent density functional theory (TD-DFT) calculations.