RESPONSE CHARACTERISTICS OF LUMINESCENT OXYGEN SENSORS

Nonlinear Stern-Volmer quenching characteristics are a common feature of oxygen sensors containing Ru(II) complexes immobilized in solid-state matrices. We discuss the origins of this behaviour and address the implications of the molecular processes on sensor performance with the help of two different sensor systems: (1) For tris(2,2'-bipyridyl)Ru(II) dichloride (Rubpy) adsorbed on silica-gel the influence of both the adsorption isotherm and heterogeneity of the indicator's environment significantly contributes to the intensity and lifetime Stern-Volmer behaviour. A modified method to determine an average lifetime from parameters received by a multi-exponential decay analysis is employed to show that static quenching is absent in this system. (2) For tris(4,7'-diphenyl-1,10'-phenanthroline) diperchlorate (RuPh(2)phen) dissolved in polystyrene a two-component approach is shown to be adequate for the description of the intensity and mean lifetime Stern-Volmer behaviour, as well as the excited state decay. The origin of this behaviour is discussed in consideration of lifetime distributions present in disordered media. The pre-exponentially weighted mean lifetime is used to show that static quenching is also absent in this system. The importance of the thermal history of the sample is noted.