Spin-Selective Photoreduction of a Stable Radical within a Covalent Donor–Acceptor–Radical Triad

Abstract

Controlling spin–spin interactions in multispin molecular assemblies is important for developing new approaches to quantum information processing. In this work, a covalent electron donor–acceptor–radical triad is used to probe spin-selective reduction of the stable radical to its diamagnetic anion. The molecule consists of a perylene electron donor chromophore (D) bound to a pyromellitimide acceptor (A), which is, in turn, linked to a stable α,γ-bisdiphenylene-β-phenylallyl radical (R • ) to produce D-A-R • . Selective photoexcitation of D within D-A-R • results in ultrafast electron transfer to form the D +• -A –• -R • triradical, where D +• -A –• is a singlet spin-correlated radical pair (SCRP), in which both SCRP spins are uncorrelated relative to the R • spin. Subsequent ultrafast electron transfer within the triradical forms D +• -A-R –, but its yield is controlled by spin statistics of the uncorrelated A –• -R • radical pair, where the initial charge separation yields a 3:1 statistical mixture of D +• - 3 (A –• -R • ) and D +• - 1 (A –• -R • ), and subsequent reduction of R • only occurs in D +• - 1 (A –• -R • ). These findings inform the design of multispin systems to transfer spin coherence between molecules targeting quantum information processing using the agency of SCRPs.