Tris(bipyridine)ruthenium(II) doped sol-gel materials for oxygen recognition in organic solvents

Optical measurements that exploit the ability of oxygen to quench the photoexcited states of Ru(byp)32+ complex provide an alternative to the standard methods of measuring molecular oxygen concentration, specially in organic solvents. In the present work we have re-examined the luminescence quenching of Ru(byp)32+ as a means of monitoring oxygen in hexane at room temperature. Oxygen-sensitive tetraethoxysilane (TEOS), methyltriethoxysilane (MTMS) and tetramethoxysilane (TMOS)-based materials were prepared under different conditions. The materials were used in a flow-injection system and characterized in terms of quenching by oxygen dissolved in hexane, response time, and stability. The TMOS system prepared under basic conditions showed enhanced analytical properties for oxygen sensing in hexane compared to the rest of materials. Evidence is presented from quenching experiments that the Ru(byp)32+ luminescence quenching mechanism may be different when the sensing phase is exposed to oxygen either in organic solvent or in the gas phase. Also, comparisons are made with data for oxygen-sensitive organogels, indicating an enhanced solubility for organogels compared with typical sol-gel materials. The results presented here emphasized the significance of the matrix for oxygen sensing in organic solvents.