Chiral Fjord-Edged Nanographenes Constructed by Allylic-Migration-Mediated Cyclization

Fjord-edged nanographenes (NGs) with non-planar π-conjugated frameworks and intrinsic chirality are attractive for nonlinear optics and chiroptical applications. However, synthetic routes to these highly twisted NGs remain elusive, largely restricted to Scholl-type cyclization, which typically requires bulky substituents to prevent over-dehydrogenation into conventional armchair edge structures. Here we report an allylic-migration-mediated cyclization strategy for the construction of fjord-edged NGs. In this strategy, a first allylic migration drives an intramolecular cyclization that pre-installs the fjord region. A second migration then enables a subsequent cyclization, and the final selective dehydrogenation completes the aromatization while preserving the fjord-edged topology. DFT calculations support the essential role of each migration in enabling the corresponding cyclization. Using this strategy, we successfully synthesized fjord-edged NGs 1 and 2, built on chrysene and bischrysene cores, respectively. Their structures are unambiguously confirmed by single-crystal X-ray diffraction. Notably, 2 exhibits near-infrared (NIR) emission extending into the NIR-II region. Despite the absence of substituents at the fjord region, both compounds possess high racemization barriers and are readily resolved into pure enantiomers by chiral HPLC. It is remarkable that 2 exhibits an exceptional dissymmetry factor (|g_abs| = 2.5 × 10^-2), exceeding those of pristine [5]helicene and previously reported fjord-edged NGs.