Fluorescent Short‐Stranded Helical Foldamers Based on L‐shaped Dibenzopyrrolo[1,2‐a][1,8]naphthyridine

Helical structures were constructed by using π‐spacer‐bridged dimers of dibenzopyrrolo[1,2‐a][1,8]naphthyridine, which has a highly fluorescent L‐shaped π‐extended skeleton. Three dimers with biphenylene (dimer 1), phenanthrene (dimer 2), and m‐phenylene (dimer 3) spacers, as well as a fixed‐helical dimer 4 where two quinolone rings were covalently cross‐linked, were designed and prepared. 1H NMR and ROESY spectra revealed that dimers 1 and 2 adopted helical forms in solution, whereas dimer 3 did not. The helical conformation of 1 was strengthened by addition of either polar or nonpolar solvents to the chloroform solution, which suggested that π–π stacking was the main contributor to the stabilization of the helical structure. All of the dimers, including fixed‐helical dimer 4, emitted fluorescence with high quantum yields (ϕ=0.79–0.86). Helical structures are constructed by using π‐spacer‐bridged dimers of dibenzopyrrolo[1,2‐a][1,8]naphthyridine, which has a highly fluorescent L‐shaped π‐extended skeleton. Three dimers 1–3 with biphenylene, phenanthrene, and m‐phenylene spacers, and a fixed‐helical dimer in which two quinolone rings are covalently cross‐linked, were designed and prepared. All of the dimers, including fixed‐helical dimer 4, emitted fluorescence with high quantum yields (ϕ=0.79–0.86, see scheme).