Singlet Photoredox Catalysis via Supramolecular Host-Guest Interactions

Photocatalysts most often leverage long-lived triplet excited states to promote valuable reactivity in organic synthesis. Consequently, many potential photosensitizers remain unviable for catalytic applications because of the kinetic constraints of diffusion-controlled intermolecular electron transfer. Supramolecular mechanisms can obviate this constraint through ground-state association with a reactant, enabling species with short-lived excited-state lifetimes to engage in synthetically relevant transformations. Thus far, the instability of host architectures toward open-shell intermediates has limited their use as photoredox catalysts. Through the synthesis of an oxidatively robust GeIV catecholate cage (Ep/2 = 0.357 V vs Fc/Fc+), we have enabled the (4 + 2) synthesis of isoquinolones via singlet photoredox catalysis. These results establish supramolecular preorganization as a generalizable platform for harnessing the unique redox potentials of singlet excited states in organic synthesis.