Photophysics and photochemistry of oxygen sensors based on luminescent transition-metal complexes

Abstract

A detailed study of the photophysics and photochemistry of \npolymer-immobilized luminescent transition-metal complex \noxygen sensors is presented. Emphasis is on understanding \nthe underlying origin of the nonlinear Stern-Volmer quenching response. Microheterogeneity is important in both photophysical and photochemical behavior, and the nonlinear \nquenching responses in RTV 118 silicone rubber can be adequately described by a two-site model, although detailed \nlifetime measurements suggest a more complex Underlying \nsystem. Counterion studies with quenching counterions are \nshown to be useful probes of the structure of the complex in \nthe polymer. While oxygen enhances photochemical instability, singlet oxygen is not directly implicated in sensor decomposition. In the photochemistry there is at least one reactive and one much less reactive site, although the photochemistry and quenching measurements probably sample different populations of sites. The existence of reactive sites suggests that stability can be enhanced by a preliminary photolysis to eliminate the more reactive sites.