New luminescent metal complex for pH transduction in optical fiber sensing: application to a CO2-sensitive device

The luminescence emission (652 nm) and lifetime (390 ns) of a novel Ru(II) tris-chelate complex tris(2-(2-pyrazinyl)thiazole)ruthenium(II) are quenched by H30 and other acids (phosphoric acetic phthalic and dihydrogenphosphate) in aqueous solution. The quenching process is shown to occur via a proton transfer to the excited (triplet state) complex since the ground state complex undergoes no protonation in the 0-12 pH interval (pKai 1. 9). Quenching rate constants in the range 1 x 108 to 5x iO M1s1 have been measured. The pH transducing system has been tested in solution using carbon dioxide and has been applied to the construction of a bifurcated fiber optic chemical sensor for this gas. Advantages of employing Ru(pzth)32 as a luminescent dye includeamong others: (1) a hydrogen carbonate buffer is not required in the reservoir chamber and (2) excitation in the visible region using inexpensive plastic optical fibers and collection of the emission through cut-off filters is feasible.