Reversibly Photoswitchable Dual-Color Fluorescence and Controlled Release Properties of Polymeric Nanoparticles

Here, we report a novel polymeric nanoparticle prepared by the self-assembly of amphiphilic copolymers containing a fluorescent naphthalimide (NAPH) and a photochromic spiropyran (SP), which possesses reversibly photoswitchable dual-color fluorescence and controlled release properties. The amphiphilic copolymers were synthesized by incorporating NAPH and SP into methyl ether poly(ethylene glycol)-poly(β-amino esters) (MPEG-PAE) via quaternization. The nanoparticles would change between yellow and purple reversibly upon UV and visible light irradiation because of the photoisomerization between SP and merocyanine (MC). The corresponding fluorescence would be switched between green and orange-red reversibly upon blue light excitation through the fluorescence resonance energy transfer from the excited NAPH to the photoisomerized MC. Meanwhile, the prepared spherical nanoparticles could be swollen under UV irradiation as the hydrophobic SP isomerized to hydrophilic MC; the nanoparticles could also be swollen u...