By adding silver ion to the non-fluorescent solution of a pyridine functionalized a-cyanostilbene derivative, an immediate gelation accompanying a high-contrast fluorescence turn-on was effectively generated. The silver ion-coordinated highly fluorescent gel underwent reverse gel-to-sol transition restoring the non-fluorescent sol state upon reaction with tetrabutylammonium fluoride. Silver nanoparticles embedded in the fluorescent gel film were fabricated by in situ UV-light irradiation, which induced the surface plasmon effect on the fluorescence emission.