A photophysical study of the interaction between dihydrogen phosphate anions and a series of ruthenium polypyridyl complexes containing anion receptor 4,4'-bis[(2-methoxyethyl)carbamoyl]-2,2'-bipyridine (L1) is reported. The complexes investigated are of the type [Ru(L)[2](L1)]X[2] and [Ru(L1)[3]]X[2], where L is 2,2'-bipyridyl or 1,10-phenanthroline and X is chloride or PF[6]-. The emission properties of the compounds are studied as a function of the anion concentrations using emission lifetime and steady-state measurements. For the mixed ligand complexes the emission intensity and lifetime increases upon the addition of 2.5 molar equivalents of H[2]PO[4]-, further additions do not result in further increases. For [Ru(L1)[3]]X[2] the emission increases upon addition of the first 2.5 equivalents of dihydrogen phosphate, however, further increases lead to a decrease in both emission intensity and lifetime. The effect of the addition of trace amounts of water is also examined.