Investigation of the acidochromic properties of methoxy-substituted benzylidene hydrazines synthesized via microwave-assisted method

Substituted 2,4-dinitrophenylhydrazone Schiff bases were synthesized using a green, microwave-assisted technique that offers rapid conversion, high yields, and environmental sustainability. Structural elucidation was performed using FTIR, UV-Vis, and 1 H NMR spectroscopy, confirming the formation of azomethine-linked hydrazone frameworks. Their acidochromic behavior was investigated in various polar protic and aprotic solvents under incremental HCl doping. The compound 1c showed the highest bathochromic shift and the most pronounced acidochromic response, including hypsochromic/hyperchromic shifts, isosbestic points, and visible color change upon HCl doping. Time-dependent DFT (TD-DFT) calculations at the B3LYP/6–311 +G(d,p) level provided strong theoretical support for the experimental findings, co-relating the solvatochromic and acidochromic properties. Notably, molecular electrostatic potential maps and frontier orbital analysis underscored key electronic variations among ortho-, meta-, and para-substituted derivatives, linking substitution pattern to charge distribution and sensing potential. These Schiff bases exhibit sensitive chromogenic response to acidic environments, positioning them as promising candidates for proton detection in smart sensors and optoelectronic devices. • Schiff bases 1a – 1c synthesized via green microwave-assisted method. • Structures confirmed by UV–Vis, FTIR and 1 H NMR spectroscopy. • Compound 1c showed strong acid response with visible color change. • TD-DFT corelated solvatochromism and spectral shifts in solvents. • Compound 1c had lowest HOMO–LUMO gap and highest electrophilicity.