Oxygen-sensitive layers for optical fibre devices

The spectroscopic features and photoreactivity with oxygen of a novel, highly lipophilic, luminescent metal complex Ru(5-odap)(3)(2+) (where 5-odap stands for 5-octadecanamide-1,10-phenanthroline), are reported and compared to those of the well-known tris(1,10-phenanthroline) analogue. An array of silicone membranes, containing Ru(5-odap)(3)(2+) or Ru(phi(2)p)(3)(2+) (where phi(2)p stands for 4,7-diphenyl-1,10-phenanthroline) as solid-supported luminescent indicators, have been fabricated. Their (non-linear) response to oxygen was evaluated with fibre-optics as a function of their adsorbent nature (silica gel, glass, reverse-phase silica, styrene/divinyl benzene copolymer, or none), surface coverage by the deposited metal complex, and loading of dyed support into the sensitive layer. The largest oxygen sensitivity (I-0/I ca. 6 for a partial pressure of 130 Torr) is achieved with the highest amount of silica gel- or glass-supported Ru(phi(2)p)(3)(2+) and the highest membrane loading. Ru(5-odap)(3)(2+) dissolved directly into silicone yields a linear dose/response plot, but with a small slope (I-0/I ca. 1.4 for a partial pressure of 720 Torr). These results are discussed in terms of dynamic surface quenching between the co-adsorbed indicator and oxygen molecules.