A photoisomerizable monolayer consisting of carboxypropyl nitrospiropyran (1a) linked to an aminopropyl siloxane layer associated with an indium tin oxide surface is used to photoswitch the electrocatalyzed reduction of H2O2 in the presence of Pt nanoparticles (NPs) or to photostimulate the generation of chemiluminescence in the presence of Pt NPs, H2O2, and luminol. Photoisomerization of 1a to the protonated merocyanine, 1b, layer results in the electrostatic attraction of the negatively charged Pt NPs to the surface. This facilitates the electrocatalyzed reduction of H2O2 or the catalyzed generation of chemiluminescence in the presence of H2O2/luminol. Further photoisomerization of the 1b monolayer results in the formation of the nitrospiropyran layer that allows the washing off of the surface-bound Pt NPs. The resulting 1a-modified surface is inactive toward the reduction of H2O2 or toward the generation of chemiluminescence.