We report two ruthenium(II) polypyridyl complexes with pendant phenol/catechol functionality that act as colorimetric sensors for fluoride ions. Experiments have revealed that hydrogen bond formation occurs with a slight excess of fluoride ion. However, in higher [F-], deprotonation of the O-H functionality resulted. Time-dependent (TD-DFT) calculations at the B3LYP/LANL2DZ level have shown that new bands appear at longer wavelengths upon complexation with fluoride ions. These are of mixed character, MLCT (d pi(Ru) -> pi*(L-1/bpy)), and intra- and interligand [pi(L-1) -> pi*(bpy) and pi(L-1) -> pi*(L-1)] transitions. These complexes also act as sensors for fluoride ions in solvent-water mixtures.