Spin-selective charge transfer pathways in photoexcited helicene-perylenediimide dyads

Spin-selective charge-transfer pathways in helicene-based dyads are relevant to applications ranging from energy conversion to quantum information science. Here, we report a series of molecular systems comprising a thiahelicene donor and a perylenediimide (PDI) acceptor connected by oligophenyl bridges of varying length. The influence of donor–acceptor distance and relative orientation on the photophysical and spin-selective properties is investigated using a combined approach based on DFT calculations, transient absorption, and time-resolved electron paramagnetic resonance spectroscopies. Particular attention is given to the role of the bridge in tuning the magnetic exchange coupling within charge-transfer states and its impact on spin-selective recombination pathways to the PDI triplet state. Efficient formation of long-lived PDI triplets is observed and shown to sensitize singlet oxygen generation with high efficiencies. These results establish structure–property relationships governing spin-selective processes in helicene-based dyads.