Only one type of lanthanide-doped upconverting nanoparticle (UCNP) is needed to reversibly toggle photoresponsive organic compounds between their two unique optical, electronic, and structural states by modulating merely the intensity of the 980 nm excitation light. This reversible "remote-control" photoswitching employs an excitation wavelength not directly absorbed by the organic chromophores and takes advantage of the fact that designer core-shell-shell NaYF(4) nanoparticles containing Er(3+)/Yb(3+) and Tm(3+)/Yb(3+) ions doped into separate layers change the type of light they emit when the power density of the near-infrared light is increased or decreased. At high power densities, the dominant emissions are ultraviolet and are appropriate to drive the ring-closing, forward reactions of dithienylethene (DTE) photoswitches. The visible light generated from the same core-shell-shell UCNPs at low power densities triggers the reverse, ring-opening reactions and regenerates the original photoisomers. The "remote-control" photoswitching using NIR light is as equally effective as the direct switching with UV and visible light, albeit the reaction rates are slower. This technology offers a highly convenient and versatile method to spatially and temporally regulate photochemical reactions using a single light source and changing either its power or its focal point.

Near-infrared (NIR) light is used to toggle photoswitches back and forth between their two isomers even though the chromophores do not significantly absorb this type of light. The reactions are achieved through a "remote control" process by using photon upconverting hexagonal NaYF(4) nanocrystals doped with lanthanide ions. These nanoparticles absorb 980 nm light and convert it to wavelengths that can be used to trigger the photoswitches offering a practical means to potentially achieve 3D-data storage, drug-delivery, and photolithography.

Cage fighter: Lanthanide‐doped upconverting nanoparticles convert near‐infrared light into ultraviolet light, which drives the photoinduced release of a “caged” species on the nanoparticle surface. This approach overcomes the problem that low‐energy light is necessary for penetrating deeper into tissue without damage but cannot be used to directly trigger important organic photochemical reactions.

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