(621d) Micellar Encapsulation of Organic Upconversion Systems to Increase the Penetration Depth of UV Light in Aqueous Environments

Ultraviolet (UV) light induces photochemical transformations used in 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 potential solution to enhance penetration depth by converting two blue photons that are more transmissive into one higher energy UV photon. However, organic molecules that facilitate upconversion usually have poor water solubility, limiting their deployment in aqueous environments. To address this challenge, we encapsulate hydrophobic sensitizer and annihilator molecules in triblock copolymer micelles to enable on-demand generation of UV photons deep into materials. We demonstrate successful micellar encapsulation of nineteen blue-to-UV triplet fusion upconversion systems to access a range of upconverted UV emission profiles with wavelengths as low as 350 nm. Micelle formation is 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. UV/vis absorption and fluorescence reveal 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, micelles encapsulating upconversion systems enable broad opportunities for spatially controlled manipulation of UV light deep into soft materials.