Donor−π–Acceptor-Type Configured, Dimethylamino-Based Organic Push–Pull Chromophores for Effective Reduction of Mild Steel Corrosion Loss in 1 M HCl

In this work, donor−π–acceptor-type four crystalline compounds have been tested for the first time to restrict the corrosion of mild steel in 1 M HCl. The details of the compounds are: C1, 4-<i>N</i>,<i>N</i>-dimethylamino-β-nitrostyrene; C2, 2-(4-(dimethylamino) benzylidene)­malononitrile; C3, ethyl 2-cyano-3-(4-(dimethylamino) phenyl)­acrylate; and C4, methyl 2-cyano-3-(4-(dimethylamino)­phenyl)­acrylate. The corrosion inhibition potentials of the compounds have been primarily investigated by electrochemical techniques, such as linear polarization resistance, Tafel polarization curves, and electrochemical impedance spectroscopy. The secondary investigation is performed by scanning electron microscopy, fluorescence surface imaging, spectroscopic techniques (UV–visible and Fourier transform infrared spectroscopy), and X-ray diffraction patterns. The results disclosed that 50 mg L^–1 of the compounds (1–4) in 1 M HCl provided the maximum inhibition efficiency as 93% (1), 88% (2), 82% (3), and 86% (4). The function of the compounds as corrosion inhibitors is explained with equilibrium corrosion potential, adsorption isotherms, and the frontier molecular orbital energies of the compounds (<i>E</i>_HOMO and <i>E</i>_LUMO) estimated by cyclic voltammetry curves and UV–visible spectra