The normal photochromism of a spirooxazine in gel thin films obtained by polymerizing the methyltriethoxysilane was analyzed as a function of the degree of cross-linking of the gel matrix. When doped-gel films contain a high fraction of silanol groups, the thermal decay of the coloration is governed by the hydrogen bond interaction between the metastable merocyanine and the silanol groups. By increasing the number of siloxane groups, the gel matrix imposes a gaussian distribution of localized barriers to the steric requirements of the reaction.