Tetraphenylethylene-substituted salen complexes of Cu(II), Zn(II), and Ni(II): structural, photophysical, electrochromic and electrofluorochromic properties

A new tetraphenylethylene (TPE)-substituted salen ligand and its mononuclear Cu(II), Zn(II), and Ni(II) complexes were synthesized and comprehensively characterized with respect to their structural, photophysical, electrochemical, electrochromic, and electrofluorochromic properties. The ligand framework, incorporating two symmetrically positioned TPE moieties, introduces significant steric bulk around the metal center and imparts aggregation-induced enhanced emission (AIEE) activity. Single-crystal X-ray diffraction analysis of the Cu(II) complex confirms a square-planar coordination geometry typical for salen-type systems. Spectroscopic studies reveal that the optical properties are predominantly ligand-centered and strongly modulated by the electronic configuration of the coordinated metal ion. Among the investigated complexes, only the Zn(II) derivative exhibits pronounced fluorescence in both solution and the solid state, consistent with its d 10 electronic configuration, which suppresses non-radiative deactivation pathways. The Zn(II) complex further demonstrates clear aggregation-induced enhanced emission behavior in a tetrahydrofuran/hexane solvent system. Electrochemical and spectroelectrochemical investigations show metal-dependent redox responses, involving ligand-centered and/or metal-centered processes, which directly influence the electrochromic characteristics of the complexes. Notably, the Zn(II) derivative displays electrofluorochromic behavior, with efficient fluorescence quenching upon electrochemical oxidation due to formation of ligand-based radical species. These findings demonstrate that incorporation of different metal ions into a TPE-functionalized salen framework enables fine-tuning of optical and redox properties, highlighting the potential of such systems as multifunctional molecular materials for electrochromic and electrofluorochromic applications. • TPE-salen Cu(II), Zn(II), and Ni(II) complexes were synthesized. • Metal-dependent ligand-centered redox behavior has been observed. • Spectroelectrochemistry reveals visible–NIR electrochromism. • Zn(II) system exhibits distinct electrofluorochromism.