) with continued exposure to a 470 nm LED. Fluorescence emission spectra showed that both UV light and blue light with ppy2/PPO upconversion micelles photolyzed caged fluorescein, with longer light exposure times corresponding to greater fluorescence intensity (Fig. ). Direct irradiation with UV light photolyzed caged fluorescein more quickly than irradiation with blue light with ppy2/PPO upconversion micelles, even when the photon flux of blue incident light exceeded that of UV incident light (Fig. , top and bottom rows, respectively). This difference in photolyzing kinetics between direct UV irradiation and upconversion micelles is attributed to relatively low UC quantum yields (Fig. ). Yet, this attribute can still be potentially advantageous in some contexts. Low UC quantum yields provide larger dynamic ranges available to control photolysis kinetics by adjusting micelle concentration and input power. The potentially large dynamic range of UC photon flux is favorable for applications such as spatiotemporal control over drug delivery, in which a high flux of UV light can be damaging to surrounding cells. Finally, we demonstrate the command of in-depth and spatially confined UV light generation using blue-to-UV UC micelles. Blue-to-UV upconversion is a powerful method for triggering UV photochemistry in scenarios that require greater incident light penetration depths than direct irradiation with UV light can achieve (Fig. ). A 365 nm LED beam was visualized with fluorescence triggered by the beam (Fig. ) and noticeably attenuated across a 1 cm cuvette containing a solution of caged fluorescein (Fig. , top). In contrast, a 470 nm LED beam did not attenuate as severely through a 1 cm cuvette containing a solution of caged fluorescein and ppy2/PPO upconversion micelles (Fig. , bottom). The visualized 470 nm LED beam was a combination of the beam itself, sensitizer fluorescence, and upconverted UV emission. While the UV light intensity reduced by 50% after penetrating 3 mm deep into the solution, the blue light intensity decreased by less than 5% (Fig. ). Surprisingly, the presence of absorptive sensitizer molecules did not significantly impact the transmission of a 470 nm beam through the cuvette containing ppy2/PPO upconversion micelles. An apparent benefit of encapsulating upconversion materials is that the overall concentration of absorptive compounds in the path of incident light is minimized, while sufficient concentrations are maintained locally in the micelle core to facilitate upconversion. These images demonstrate the potential for blue-to-UV upconversion to trigger UV photochemistry deeper within media than direct UV excitation.