Metal ion sensors based on a luminescent ruthenium(II) complex: The role of polymer support in sensing properties

Oxygen and copper(II) ion quenching studies were conducted on a model sensor system to elucidate the significant, yet not fully characterized, role of polymer supports in sensor performance. The system consisted of [Ru(Ph(2)phen)(2)(4-cyclamCH(2)(4'-Me)bpy)]Cl-2 (Ph(2)phen = 4,7-diphenyl-1,10-phenanthroline; bpy = 2,2'-bipyridine; cyclam = 1,4,8,11-tetraazacyclotetradecane) as the sensor molecule, copper(IT) ions as the quenching analyte, and two polymer supports. One polymer used was a cyclic siloxane cross-linked with a hydrophilic poly(ethylene oxide); the other was a ternary polymer with poly(ethylene oxide), poly(dimethylsiloxane), and 2-hydroxy-ethylmethacrylate. Both polymers contain a hydrophobic binding region for the sensor molecule and a hydrated hydrophilic region for transport of the ions to the sensor. Luminescence intensity and lifetime measurements show the polymer supports to be equally effective at shielding the sensor molecule from oxygen quenching but not copper(H) ion quenching. Unlike oxygen, the copper(II) ions quench the sensor molecule in solution and in the polymer supports through a combination of static and dynamic quenching. The unquenched excited state lifetimes, bimolecular rate constants, and equilibrium constants are presented, and their differences are interpreted to provide information about the local environment of the sensor molecule immobilized in the polymer supports.