Performing UV photochemistry with blue light using triplet fusion upconversion micelles

Ultraviolet (UV) light induces photochemical transformations for applications such as photocatalysis, photopolymerization, and biomaterial manipulation. Despite its utility, UV light attenuates substantially through organic and aqueous media, preventing UV photochemistry deep within most soft materials. Blue-to-UV triplet fusion upconversion offers a solution by converting two blue photons that are more transmissive into a higher energy UV photon. To use blue-to-UV upconversion in aqueous environments, we encapsulate hydrophobic sensitizer and annihilator molecules in F127 triblock copolymer micelles, which are validated by dynamic light scattering and upconversion photoluminescence measurements. To demonstrate UV photochemistry in aqueous media via blue-to-UV upconversion, a caged fluorescent dye was selected as a "reporter" that appears colorless prior to illumination and becomes fluorescent upon UV exposure. Fluorescence and UV/Vis confirm that blue light uncages the dye only when blue-to-UV upconversion micelles are present in solution. Finally, the two-photon nature of blue-to-UV upconversion is exploited to produce UV light exclusively at a focal point of blue light. Broadly, polymer-encapsulated upconversion materials have exciting potential as optically active materials.