Oxygen Sensors Based On Fluorescence Quenching Of Ruthenium(Ⅱ) Diimine Complexes

In the past decades, a variety of oxygen sensors based on luminescence quenching by oxygen have been developed and reported in analytical chemistry, biochemistry, clinical medical diagnose, environmental and also in other fields. Optical chemistry sensors were widely investigated because of their high sensitivity and high selectivity. These optical chemistry sensors were formed by oxygen-sensitive dyes and carrier materials. Many luminescent dyes have been tested as oxygen sensing probes. Among them, ruthenium(II) diimine complexes were often used as oxygen-sensitivity dyes, owing to their visible light absorption, relatively long excited lifetime, high sensitivity to oxygen and large Stoke' shifts.In this paper, [4,4'-dimethyl-2,2'-bipyridine-bis(2,2'-bipyridine)] ruthenium(II) dichloride { [Ru-mbpy]²⁺ } and [4,4'-dimethylformate-2,2'-bipyridine-bis (2,2'-bipyridine)] ruthenium(II) dichloride { [Ru-dmfbpy]²⁺ } were synthesized and characterized. The organic-inorganic hybrid materials were prefabricated by sol-gel process. Precursor sols were prepared by hydrolyzing the mixture of tetraethoxylsilane and n-octyltriethoxysilane. The organically modified silicates (ormosil) have both organic and inorganic characters such as easy realization of versatility in optical and mechanical properties. For example, the ormosil were often used as supports for the fabrication of optical oxygen sensors. Ruthenium(II) bipyridine complexes were doped in the organic-inorganic hybrid materials after the precursor sols were prepared. Oxygen quenching studies were carried out by blowing nitrogen or oxygen over the samples.Fluorescence intensity vs response time relationship and Stern-Volmer equation relationship were both tested to study the oxygen sensors' characteristics. The concentrations of ruthenium(II) bipyridine complexes, the cured temperature and aged time were also investigated. These factors made different influences on the oxygen sensors' characteristics. Compareing oxygen sensors which made from two ruthenium(II) bipyridine complexes, we found that these oxygen sensors had the similar characteristics such as fast response time and long term stability. The concentrations of ruthenium(II) bipyridine complexes in ormosil also had different influences on oxygen sensors' characteristics. The linearity of all samples were non-linear and different although the best sensitivity was obtained with [Ru-dmfbpy]²⁺.