Lifetime-based pH sensor system based on a polymer-supported ruthenium(II) complex

A new luminescence lifetime-based pH sensor system is described. The system is based on [Ru(Ph2phen)2DCbpy]2+ (DCbpy = 4,4'-dicarboxy-2,2'-bipyridine) immobilized in a mixed domain network copolymer utilizing hydrophobic regions in a hydrophilic, water-swellable, poly(ethylene oxide) matrix. The metal complex binds irreversibly to the hydrophobic domains leaving the pH-sensing COOHs projecting into an aqueous-rich poly(ethylene oxide) region. The complex shows a strong pH dependence of its lifetime (3-4-fold) and provides a usable pH range of about 3-5. The long (approximately 1 micros) excited-state lifetime and visible absorption of the sensor simplifies measurements. A model for the combined pH and oxygen-quenching sensitivity of the complex is provided; this allows use of the pH system over a wide range of oxygen concentrations. The combined polymer sensor is easy to prepare and requires no covalent chemistry. Further, the polymers enhance the luminescence of the complex and minimize interference from oxygen quenching.