Quinolin-2(1H)‑one-Based Push-Pull Fluorophores: Tuning Emission from Positive to Inverted Solvatochromism

Two donor-acceptor diethylaminoquinolin-2-(1H)-ones featuring carbonyl or nitroisoxazole groups as acceptors were synthesized (DQCh and DQI), and their emissive spectral behavior was recorded in a wide range of solvent polarities. The carbonyl-containing compound nitroisoxazole derivative (DQI) represents a newly reported synthesis in this work. Interestingly, the two fluorophores exhibited distinct solvatochromic emission behaviors, with DQCh showing a significant bathochromic shift with the increase in solvent polarity, while DQI 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 DQCh and DQI to hydrogen bonding from the solvent. These findings position quinolin-2-(1H)-ones as a promising scaffold for designing polarity-sensitive emissive dyes, offering new insights into the fundamental understanding and rational design of solvatochromic materials.