Multifunctional Binuclear Ru(III) Complexes with Alkynyl-Imine Bridges: Electrochemical, Luminescent, and Nonlinear Optical Properties.

A new series of Multifunctional binuclear Ru(III) complexes of the type [Ru₂(L1/L2)(phen)₂X₄] (1a–d) and [Ru₂(L1/L2)(bipy)₂X₄] (2a–d) has been synthesized and systematically characterized, where L1 and L2 are alkynyl-functionalized Schiff base ligands, phen = 1,10-phenanthroline, bipy = 2,2′-bipyridine, and X = N₃⁻ or NCS⁻. EPR and magnetic susceptibility measurements suggest an octahedral coordination geometry around the Ru(III) centers. The thermally stable complexes exhibit quasi-reversible Ru(III)/Ru(IV) and Ru(III)/Ru(II) redox processes, which are influenced by the π-accepting nature of the coordinated polypyridine ligands. The complexes display red-shifted emission predominantly originating from ligand-centered and metal-to-ligand charge transfer (ILCT/MLCT) transitions at room temperature, with emission behavior influenced by alkynyl functionalization of the Schiff base ligand and further modulated by the coordinated polypyridine framework and the nature of the pseudohalide co-ligands (N₃⁻/NCS⁻). In addition, second harmonic generation (SHG) measurements performed using the Kurtz powder technique reveal significant nonlinear optical responses for all complexes. The combined structural, electrochemical, photophysical, and nonlinear optical properties highlight these Multifunctional binuclear Ru(III) systems as promising candidates for optoelectronic and photonic applications.