Supramolecular Strategies To Construct Biocompatible andPhotoswitchable Fluorescent Assemblies

We designed and synthesized an amphiphiliccopolymer with pendant hydrophobic decyl and hydrophilicpoly(ethylene glycol) chains along a common poly(methacrylate)backbone. This macromolecular construct captures hydrophobicboron dipyrromethene fluorophores and hydrophobicspiropyran photochromes and transfers mixtures of bothcomponents in aqueous environments. Within the resultinghydrophilic supramolecular assemblies, the spiropyran componentsretain their photochemical properties and switchreversibly to the corresponding merocyanine isomers upon ultraviolet illumination. Their photoinduced transformations activateintermolecular electron and energy transfer pathways, which culminate in the quenching of the boron dipyrromethene fluorescence.As a result, the emission intensity of these supramolecular constructs can be modulated in aqueous environments under opticalcontrol. Furthermore, the macromolecular envelope around the fluorescent and photochromic components can cross themembrane of Chinese hamster ovarian cells and transport its cargo unaffected into the cytosol. Indeed, the fluorescence of thesesupramolecular constructs can be modulated also intracellularly by operating the photochromic component with optical inputs. Inaddition, cytotoxicity tests demonstrate that these supramolecular assemblies and the illumination conditions required for theiroperation have essentially no influence on cell viability. Thus, supramolecular events can be invoked to construct fluorescent andphotoswitchable systems from separate components, while imposing aqueous solubility and biocompatibility on the resultingassemblies. In principle, this simple protocol can evolve into a general strategy to deliver and operate intracellularly functionalmolecular components under optical control.