Tuning the photophysical and chiroptical properties of [4]helicene‐diketopyrrolopyrroles

Abstract

AbstractSynthesis and functionalization of diketopyrrolo[3,4‐c]pyrrole (DPP) derivatives containing chiral groups able to induce a strong chiral perturbation of the DPP core are still a challenging task. We report in this work the straightforward preparation of four bis([4]helicene)‐DPP and bis([4]thiahelicene)‐DPP dyes upon the condensation of 2‐CN‐[4](thia)helicene precursors, followed by their N‐alkylation by nucleophilic substitution (compounds 9–11) or by a Mitsunobu‐type strategy (compound 12). Compound 12, which contains sec‐phenylethyl groups attached to the nitrogen atoms, has been obtained as (R,R) and (S,S) enantiomers. The four DPP‐helicenes are luminescent in solution, while the N‐benzyl (10) and N‐sec‐phenethyl (12) are emissive in the solid state as well. The chiroptical properties of compound 12 in solution and in the solid state indicate a strong chiral perturbation provided by the α‐stereogenic centres, in spite of the stereodynamic nature of the [4]helicene flanking units.