Oxygen sensors based on luminescence quenching: interactions of metal complexes with the polymer supports

Oxygen quenching of [Ru(Ph2phen)3]Cl2 (Ph2phen = 4,7-diphenyl-1,10-phenanthroline) has been studied in a diverse series of polymers, most with a common poly-(dimethylsiloxane) (PDMS) component. Systematic variations in the polymer properties have been made in order to delineate the structural features important for satisfactory use of supports for oxygen sensors. Most measurements were made using homo- or copolymers containing a PDMS region, although some measurements were made on small ring siloxane polymers. In particular, quenching behavior was examined as a function of polymer structure as well as the type of and amount of polar copolymer cross-linkers. Cross-linkers were added to enhance the solubility of oxygen probes in an otherwise nonpolar polymer. In addition, hydrophobic silica was added to alter quenching properties. Domain models are used to explain the variations in oxygen quenching properties as a function of additives and cross-linkers. These considerations have led to the most sensitive ruthenium-based sensor reported to date. The relative affinity of the different domains for the complex and the efficacy of the domains for oxygen quenching control the overall behavior of the sensing response. Guidelines for design of suitable polymer supports for oxygen sensors are proposed.