A synergetic effect of light and anion: near-infrared colorimetric monitoring of nitric oxide (NO) release from fluoride/cyanide anions and a water responsive ruthenium nitrosyl complex

Abstract

Near-infrared (NIR) spectral-responsive multitasking chemical systems are always advantageous in biological and environmental systems. Although ruthenium complexes are highly attractive compounds for many applications, studies on NIR optical responsive sensors are very limited because of their synthetic difficulties. The sensing of fluoride and cyanide ions using ruthenium nitrosyl complexes is not known. In this study, we report the synthesis and characterization of a new terpyridine-based ruthenium nitrosyl complex [Ru(Cl)₂NO(terpy-C₆H₄OH)] 1·Ru-OH. The complex exhibited distinct NIR absorptions at 680 nm, as well as a visible color change with the fluoride ion in DMSO–CH₃CN medium. However, when the solvent is changed to DMSO–H₂O, it responds only with a cyanide ion with a distinct colorimetric change. Binding of the F⁻ ion leads to deprotonation of 1·Ru-OH; the deprotonated complex is also used for the colorimetric detection of a trace amount of water in DMSO and acetonitrile with a limit of detection (LOD) of 0.034 wt% and 0.007 wt%, respectively. Ruthenium nitrosyl complexes have appeared as promising platforms for light-controlled release of nitric oxide (NO), which can be beneficial for therapeutic application. NO release studies of 1·Ru-OH by UV-vis and FT-IR spectroscopy confirm that it can release NO in a light-controlled manner. In addition, the NO release could be monitored by the naked eye with a color change and spectral change in the NIR region. Importantly, NO release studies revealed that the rate of NO release could be modulated in the presence of the F⁻ ion. Here, the fluoride ion acts as an allosteric regulator. These results demonstrate that 1·Ru-OH is both a promising multitasking colorimetric and NIR sensor and a colorimetric responsive NO-releasing agent.