Synthesis, Photophysical and Electrochemical Properties of a Mixed Bipyridyl-Phenanthrolyl Ligand Ru(II) Heteroleptic Complex Having trans-2-Methyl-2-butenoic Acid Functionalities

Abstract: In this work, two ligands: 4-(trans-2-Methyl-2-butenoic acid)-2,2'-bipyridine) (L₁) and 5-(trans-2-methyl-2-butenoic acid)-1,10-phenanthroline (L₂), with the corresponding mixed-ligand heteroleptic Ru(II) complex were synthesized and characterized by FT-IR, ¹H-, ¹³C-NMR spectroscopy and elemental analysis. The influence of the mixed functionalized polypyridyl ruthenium(II) complex on the photophysical and electrochemical properties were investigated and compared to individual single-ligand homoleptic complexes. Interestingly, the mixed-ligand complex formulated as [RuL₁L₂(NCS)₂] exhibits broad and intense metal-to-ligand charge transfer (MLCT) absorption with a high molar extinction coefficient (λ_max = 514 nm, ε = 69,700 M⁻¹ cm⁻¹), better than those of individual single-ligand complexes, [Ru(L₁)₂(NCS)₂] and [Ru(L₂)₂(NCS)₂], and a strong photoluminescence intensity ratio in the red region at λ_em = 686 nm. The electrochemical properties of the complex indicated that the redox processes are ligand-based.