Organic dyes can be entrapped into sol-gel matrices to act as reactive chromophores, for instance, molecules that change the structure with the pH of the medium. Sol-gel silica films doped with 2-[4-(dimethylamino)phenylazo]benzoic acid were deposited by dipping upon sodalime glass slides. Optical absorption and sensitivity against pH were monitored by Vis spectroscopy. Reversible reactivity of coatings versus pH in liquid and gas media is good enough to apply them as optical pH sensors. Thermal, chemical and mechanical behavior as well as photostability of coatings are evaluated.