Single-colour, visible light activation and excitation of the luminescence of a ‘switch-on’ dye and enhancement by silver nanoparticles

•Novel dihydrofluorescein probes can be easily prepared by a chemical reduction of substituted fluorescein derivatives.•The reduced probes can be photochemically reoxidized by illumination with visible light.•While the dihydrofluorescein derivatives are non-fluorescent, the oxidized photochemical products are highly emissive and can be excited using the same wavelength used for their activation.•Silver nanoparticles (AgNP) can enhance the photochemical transformation and the observed emission.