Determining oxygen diffusion coefficients in polymer films by lifetimes of luminescent complexes measured in the frequency domain.

Polymer films doped with luminescent ruthenium complexes are proving to be important oxygen sensors. We describe a technique using lifetime measurements in the frequency domain for determining the diffusion coefficient of oxygen through various polymer supports. These fundamental measurements will allow for more rational design of improved sensors. Three types of polymers were doped with [Ru(4,7-diphenyl-1,10-phenanthroline)3]Cl2. We monitored the luminescence versus time after applying a step increase in the oxygen pressure at the surface of the film. We modeled the decrease in apparent lifetime as a function of time using the diffusion coefficient of oxygen in the polymer as the only adjustable parameter. The model accurately predicted the lifetime versus time curves, and diffusion coefficients agreed well with those obtained from intensity measurements. The advantages and disadvantages of the lifetime technique to those used earlier are discussed.