Helical bilayer nanographenes (HBNGs) are chiral π-extended
aromatic compounds consisting of two π–π stacked
hexabenzocoronenes (HBCs) joined by a helicene, thus resembling van
der Waals layered 2D materials. Herein, we compare[9]HBNG,[10]HBNG, and[11]HBNGhelical bilayers
endowed with [9], [10], and [11]helicenes embedded in their structure,
respectively. Interestingly, the helicene length defines the overlapping
degree between the two HBCs (number of benzene rings involved in π–π
interactions between the two layers), being 26, 14, and 10 benzene
rings, respectively, according to the X-ray analysis. Unexpectedly,
the electrochemical study shows that the lesser π-extended system[9]HBNGshows the strongest electron donor character, in part
by interlayer exchange resonance, and more red-shifted values of emission.
Furthermore,[9]HBNGalso shows exceptional chiroptical
properties with the biggest values ofgabsandglum(3.6 × 10–2) when compared to[10]HBNGand[11]HBNGowing to the fine alignment in the configuration of[9]HBNGbetween its electric and magnetic dipole transition moments. Furthermore,
spectroelectrochemical studies as well as the fluorescence spectroscopy
support the aforementioned experimental findings, thus confirming
the strong impact of the helicene length on the properties of this
new family of bilayer nanographenes.