pH sensors based on luminescent ruthenium(II) α-diimine complexes with diethylaminomethyl sensing groups

A study of the pH sensing characteristics of long lived Ru(II) complexes on a solid polymer support is presented. The systems selected were [Ru(Ph(2)phen)(2)DEAMbpy](2+) and [Ru(Ph(2)phen)(2)(DEAM)(2)bpy](2+) (Ph(2)phen = 4,7-diphenyl-1, 10-phenanthroline, DEAMbpy = 4-methyl-4'-(diethylamino)methyl-2,2'-bipyridine, (DEAM)(2)bpy = 4,4'-bis(diethylaminomethyl)-2,2'-bipyridine). The support is a very hydrophobic cyclic siloxane crosslinked with hydrophilic polyethylene oxide. Sensor preparation, based on hydrophobic binding of the sensor molecule to the polymer's hydrophobic pockets, is fast and convenient. While in solution both complexes have large changes in responses in the physiological pH range of 7-8, the polymer bound complexes show significantly different responses with pH. Either the magnitude of the response is reduced to too low a level to be valuable, or the pH of optimum response is shifted outside the 7-8 region. This muting and shifting of response is quite different from that observed for other pH sensor complexes on the same support. The possible origins of the effect are discussed. In spite of being unsuitable in the current formulation for physiological pHs, [Ru(Ph(2)phen)(2)(DEAM)(2)bpy](2-) shows useful response in both the 3-5 and 8-10 pH ranges.