Fusing of Seven HBCs toward a Green Nanographene Propeller

This work presents a green chiral nanographene propeller (NP), which is built by fusing seven hexabenzocoronenes in a helical arrangement. It contains 258 conjugated carbon atoms and represents the largest three-dimensional conjugated polycyclic aromatic hydrocarbons ever prepared using scalable solution chemistry. Despite its unusual molecular size, single-crystal X-ray structural analysis (resolution 0.9 Å) and baseline chiral resolution are achieved. NP is soluble in various organic solvents and can be fully characterized by common spectroscopic and voltammetric techniques. It has a strong panchromatic absorption from the ultraviolet to the near-infrared (λ_max = 659 nm, ε = 179 000 M^-1 cm^-1). For instance, more than half of the spectral range between 300 and 800 nm witnesses an extinction coefficient larger than 100 000 M^-1 cm^-1. Moreover, a record-high Cotton effect in the visible spectrum is observed for enantiopure NP, with |Δε| values of 1182 and 1090 M^-1 cm^-1 at 374 and 405 nm, respectively. These photophysical properties evolve significantly compared to those of the propeller-shaped hexapole [7]helicene.