Structure-activity engineering of pyranopyrazole molecular films for copper surface protection

Designing molecular interfaces capable of protecting metallic materials against acid-induced degradation remains an important challenge in materials engineering. In this study, The corrosion-inhibition performance of three previously synthesized pyrano[2,3- c ]pyrazole derivatives 6-amino-3-methyl-4-(2-nitrophenyl)-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (ANP), 6-amino-4-(3-fluorophenyl)-3-methyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (AFP) and 6-amino-4-(3-bromophenyl)-3-methyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (ABP), was investigated for copper in 0.5 M H 2 SO 4 using electrochemical, surface, and computational approaches. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) measurements revealed concentration-dependent inhibition with maximum efficiencies of approximately 93.6% (ANP), 94.5% (AFP) and 95.1% (ABP) at only 1.0 mM. Nyquist/Bode analyses supported by equivalent-circuit fitting, indicated the formation of compact and resistive adsorbed films that restricted interfacial charge transfer. Surface characterization (SEM, AFM) confirmed a substantial reduction in surface damage and roughness, with the overall protective performance following the order ABP > AFP > ANP, consistent with electrochemical results. DFT, Fukui-function analysis, and molecular simulations identified the heteroatoms and aromatic π-systems as the main adsorption sites and revealed favorable adsorption configurations on Cu(111). The calculated Δ ⁢ 𝐺 0 a d s values (−38.67 to −39.23 kJ mol −1 ) confirmed spontaneous adsorption involving strong physical and electrostatic interactions, with a possible donor–acceptor contribution. The novelty of this work lies in comparing nitro-, fluoro-, and bromo-substituted pyranopyrazoles under identical conditions to establish a structure–interface–performance relationship. ABP showed the best performance, providing practical guidance for designing inhibitors for copper protection in acidic media.