The development of switchable white-light emitters is extremely challenging but urgently needed for various applications. We describe a class of switchable fluorescent polymeric nanoparticles (SFPNs) that can alternate their emission color among stable white, cyan, or pink. These SFPNs consist of a dye with cyan-light emission and a spiropyran (SP) derivative with photochromism. When the SP derivative is transferred to its merocyanine state, fluorescence resonance energy transfer (FRET) occurs from the cyan dye to the merocyanine one. In a rational design of transfer efficiency, a stable white-light emission is achieved. This white-light emission can be switched to the cyan-light one upon photoirradiation or pink-light one by solvent-induced swelling. Such multi-color fluorescent alternation is reversible and therefore allows for data encryption. Because of the facile synthesis, excellent long-term stability, fast photo-responsibility, high-contrast fluorescence, and outstanding switchability of these nanoparticles, we envision that they should have great potential in various applications such as high-resolution imaging, white luminescence, and data encryption.
