pH responsive luminescent switches of ruthenium(II) complexes containing two imidazole groups: Synthesis, spectroscopy, electrochemistry and theoretical calculations

A series of new mononuclear polypyridyl ruthenium(II) complexes containing two imidazole groups have been synthesized and characterized by 1H NMR, ES-MS, FAB-MS, IR spectra and elemental analysis. Their electrochemistry and spectroscopic properties including UV–Vis absorption, steady-state and time-resolved emission have been studied using both experimental methods and theoretical calculations. These complexes have been found to be sensitive luminescent pH switches, as their absorption and emission spectra respond to the solutions pH disturbances with extraordinary sensitivity, through the protonation and deprotonation of the imidazole groups. DFT calculations have been carried out to reveal the exact protonation and deprotonation route. The ground-state and excited-state ionization constants (pK a and View the MathML sourcepKa∗) of each acid–base equilibrium have also been calculated according to the absorbance and emission data under different pH.