Stimuli-Responsive Luminescent Bis-Tridentate Ru(II) Complexes toward the Design of Functional Materials

We report here the synthesis, characterization, and photophysics of two bis-tridentate Ru(II) complexes based on a heteroditopic ligand and thoroughly studied their stimuli-responsive behaviors toward the design of functional materials. Both complexes display emission at room temperature having lifetimes in the range of 0.5-70.0 ns, depending on coligand and solvent. Substantial modulations of absorption and emission spectral behaviors of the complexes were done upon interaction with anions, and anion-induced changes in the properties lead to recognition of selected anions in both organic and aqueous media. Photophysical properties of the complexes were also tuned by changing the pH of the medium, and p K_a values in both ground and excited states were determined. The presence of free pyridine-imidazole motifs in the complexes leads to substantial modulation of the optical properties and switching of the emission properties upon interaction with selected cations as well as with protons. Fe²⁺, Co²⁺, Ni²⁺, and Cu²⁺ trigger emission quenching, while Zn²⁺ induces finite enhancement of the emission intensity in the complexes. In essence, modulation of the optical properties and switching of luminescence properties of the complexes were accomplished by a variety of the external stimuli such as anions, cations, protons, and pH, as well as solvent polarity. Importantly, the optical outputs in response to an appropriate set of stimuli were utilized to mimic the functions of two-input IMPLICATION, NOR, and XNOR logic gates.