UV photochemistry was further demonstrated in localized volume elements by leveraging the quadratic nature of blue-to-UV TTA-UC. Since upconversion only proceeds efficiently at regions of high intensity, the photolysis of caged fluorescein was localized to the focal point of blue input light in a system with blue-to-UV upconversion micelles (Fig. ). Focused UV light photolyzed the caged fluorescein primarily where the beam entered the solution (Fig. , top row), and background-subtracted images revealed minimal photolysis at the focal point (Fig. , top row).