Quinolin-2(1 <i>H</i> )-one-Based Push–Pull Fluorophores: Tuning Emission from Positive to Inverted Solvatochromism

Two donor-acceptor diethylaminoquinolin-2-(1<i>H</i>)-ones featuring carbonyl or nitroisoxazole groups as acceptors were synthesized (<b>DQCh</b> and <b>DQI</b>), and their emissive spectral behavior was recorded in a wide range of solvent polarities. The carbonyl-containing compound nitroisoxazole derivative (<b>DQI</b>) represents a newly reported synthesis in this work. Interestingly, the two fluorophores exhibited distinct solvatochromic emission behaviors, with <b>DQCh</b> showing a significant bathochromic shift with the increase in solvent polarity, while <b>DQI</b> exhibited an unusual inversion in its emission energy at intermediate solvent polarities, transitioning from a bathochromic to a hypsochromic behavior. With multiparametric analysis this unique solvatochromic emission behavior was linked to the different sensibilities of the excited states of <b>DQCh</b> and <b>DQI</b> to hydrogen bonding from the solvent. These findings position quinolin-2-(1<i>H</i>)-ones as a promising scaffold for designing polarity-sensitive emissive dyes, offering new insights into the fundamental understanding and rational design of solvatochromic materials.