Design, Synthesis, and Dft Analysis of Benzaldehyde-Based Ethynyl-Functionalized Donor–Acceptor Dicyanomethyl Derivatives

Abstract

Herein, 2-(p-tolylethynyl)benzaldehyde(3A), 2-((4-(dimethylamino)phenyl)ethynyl)benzaldeh yde (3B), 2-((4-methoxyphenyl)ethynyl)benzaldehyde (3C), 2-(2-(p-tolylethynyl)benzylidene) malononitrile (4A), 2-(2-((4-(dimethylamino)phenyl)ethynyl)benzylidene)malononitrile (4B) and 2-(2-((4-methoxyphenyl)ethynyl)benzylidene)malononitrile (4C) were obtained in yields of 95%, 93%, 90%, 85%, 88% and 85%, respectively. These novel benzaldehyde-based, ethynyl-functionalized donor–acceptor dicyanomethyl derivatives (BEDA-DCMs) (4A, 4B, and 4C) were synthesized via Sonogashira coupling and Knoevenagel condensation reactions. The structural features of the synthesized compounds were characterized using melting point determination, elemental analysis, FT-IR and NMR spectroscopy. Their electronic absorption properties were investigated using UV–vis spectroscopy, while their electrochemical behavior was examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electronic structures and reactivity of the compounds were evaluated using density functional theory (DFT)-based HOMO–LUMO, molecular electrostatic potential (MEP), electron localization function (ELF), localized orbital locator (LOL), and natural bond orbital (NBO) analyses. The results show that the electronic properties of the benzaldehyde-based derivatives can be effectively tuned by introducing strong electron-donating substituents with ethynyl functionality into the molecular framework.In this context, compound 4B exhibits the lowest HOMO/LUMO energy gap (ΔE = 5.9200 eV) and the lowest hardness value (η = 2.9600 eV) among the derivatives. Therefore, 4B stands out as the most promising candidate in terms of targeted functional performance, particularly in applications where efficient charge transfer and electronic responsiveness are critical, such as catalytic processes and related applications.