A Helicene Nanoribbon with Greatly Amplified Chirality

We report the synthesis
and characterization of a chiral, shape-persistent,
perylene-diimide-based nanoribbon. Specifically, the fusion of three
perylene-diimide monomers with intervening naphthalene subunits resulted
in a helical superstructure with two [6]­helicene subcomponents. This
π-helix-of-helicenes exhibits very intense electronic circular
dichroism, including one of the largest Cotton effects ever observed
in the visible range. It also displays more than an order of magnitude
increase in circular dichroism for select wavelengths relative to
its smaller homologue. These impressive chiroptical properties underscore
the potential of this new nanoribbon architecture in the context of
chiral electronic materials.