Expanding Azobenzene Photoswitching into Near-Infrared via Endothermic Triplet Energy Transfer

Azobenzene photoswitches capable of selective and efficient photoisomerization by long-wavelength excitation is an enduring challenge. Herein, rapid isomerization from Z- to E-state of two ortho-functionalized bistable azobenzenes with near-unity photoconversion was driven by triplet energy transfer upon red and near-infrared (up to 770 nm) excitation of porphyrin photosensitizers in catalytic micromolar concentrations. We show that the process of triplet-sensitized isomerization is efficient even when the sensitizer triplet energy is substantially lower (\u003e 200 meV) than for the azobenzene. This makes the approach applicable for wide variety of sensitizer-azobenzene combinations and enables the expansion of excitation wavelengths into the near-infrared spectral range. Therefore, indirect excitation via endothermic triplet energy transfer provides efficient and precise means for photoswitching upon 770 nm near-infared light illumination with no chemical modification of azobenzene chromophore, a desirable feature in e.g. photocontrollable biomaterials.