Design and Synthesis of Novel Molecular Switches Functionalized with a Viologen Unit Based on Copper(II) Bis(ethyl 4-chloroacetoacetate) Complex

Viologen-based molecular switches have attracted significant attention due to their reversible redox properties and promising applications in electronic and sensing devices. This study focuses on the design and development of novel chemically and electrochemically responsive molecular switches constructed through non-covalent π–dimerization of viologen radicals within copper(II) β-diketone complexes in solution. Initially, the bidentate O2 donor ligand ethyl 4-chloroacetoacetate were coordinated to copper(II) to afford the base complexes CuECl, respectively. Subsequent axial coordination of CuECl with the neutral ligand 4,4′-bipyridine (bpy) led to the corresponding functionalized viologen system: CuEV+·Cl–. Moreover, SN2 nucleophilic substitution reactions of CuECl with bpy, afforded the additional complex CuEV+·Cl–. A total of eleven complexes were successfully synthesized and comprehensively characterized using FT-IR, LC-mass spectrometry, TGA, DTA, DSC, XRD, EDS, and UV–visible absorption spectroscopy, along with electrochemical and reduction studies. Finally, chemical and electrochemical reduction of the viologen unit in, CuEV+·Cl– produced intra and intermolecular π-dimers of the resulting viologen radicals. Additionally, interactions of CuECl with bpy was examined in DMF solution, and the absorption spectra of these mixtures were compared with those of the corresponding adduct complexes.