Coumarin end-capped poly(ε-caprolactone)-poly(ethylene glycol) tri-block copolymer: synthesis, characterization and light-response behavior

Light responsive polymeric materials are of great interest for several applications; in particular, the NIR spectrum is considered an ideal light source for e.g. biomedical applications. Here, we have designed light sensitive poly (epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) (PCL-PEG-PCL) triblock copolymer, end-capped with modified coumarin. When dialyzed against water, the coumarin-functionalized triblock copolymers self -assembled into core-shell nanoparticles, characterized by DLS, SEM, and NMR. The hydrophobic Nile Red, used as a model guest molecule, was loaded in the nanoparticles and its release by light irradiation of selected wavelength was demonstrated by fluorescence spectroscopy. When irradiated with UV or NIR light, coumarin end-groups of the copolymer were photolyzed, converting the end groups to carboxylic acids, thus provoking the disruption of the preassembled nanoparticles, and the release of the encapsulated guest molecule.