Light‐Powered Atroposelective Ratcheting via Excited‐State Donor–Acceptor Interactions

A light-powered atroposelective ratcheting system based on a desymmetrized pentiptycene scaffold is reported. This structural framework enforces templated donor-acceptor (D-A) arrangements capable of distinguishing between rapidly equilibrating atropisomers, enabling atroposelective Z → E photoisomerization that selectively suppresses the consumption of one atropisomer and leads to its accumulation under continuous irradiation. Ultrafast transient spectroscopic studies and theoretical calculations reveal that this photochemical atroposelectivity arises from electronic interactions between the donor and acceptor moieties in the excited state. Such an atroposelective ratchet could potentially be harnessed to construct light-driven rotary molecular motors (LRMMs). These results highlight the role of conformer-dependent photochemistry in achieving precise photochemical control over molecular motion.