Quenching of luminescent ruthenium(II) complexes by water and polymer-based relative humidity sensors

Water quenching of luminescent [Ru(phen)(2)dppz]Cl(2), [Ru(phen)(2)dppn]Cl(2), and [Ru(4,7-Ph(2)phen)(2) dppz]Cl(2) (phen = 1,10-phenanthroline; 4,7-Ph(2)phen = 4; 4,7-diphenyl-1,10-phenanthroline; dppz = dipyrido[3,2-a:2'3'-c]phenazine; dppn = benzodipyrido(a:3,2-h:2',3'-j)phenazine) complexes was studied in acetonitrile and in polymers. The polymers contained hydrophobic and hydrophilic components to control mechanical properties and were designed to absorb water with changing humidity and, thus, affect the emission intensity and lifetime. Quenching by water in mixed solvents and in polymers was shown to arise from a combination of diffusional and static ground-state associational quenching. The factors controlling polymer properties are discussed. The systems can be tailored to give a wide range of responses or function as a binary sensor at a fixed humidity level.