DESIGN OF OXYGEN SENSORS BASED ON QUENCHING OF LUMINESCENT METAL-COMPLEXES - EFFECT OF LIGAND SIZE ON HETEROGENEITY

A detailed study of the oxygen quenching for luminescent ReL(C0)(3)CNR (+) (L = alpha-diimine and R alkyl) in silicone polymers shows a high degree of heterogeneity, which depends on the size of L but not of R. All quenching is dynamic with little or no static quenching. Microhete rogeneity is important in the nonlinear quenching responses. Quenching data are well described by a two-site model, although detailed lifeti me measurements suggest a more complex underlying system. The appearan ce of two dominant sites indicates that the complex can bind in sites that are either readily or poorly quenched by oxygen. The variations o f this ratio with the size of L suggests that there is a distribution of binding site sizes and that binding of L in these sites is necessar y to protect the complex from quenching. Good quenching occurs when th e L's do not bind to protective sites and thus are left exposed to oxy gen quenching. The use of ligand size to control response characterist ics is discussed. Photochemistry is most pronounced in vacuum while ox ygen or nitrogen enhances stability.