N-Annulated [5]Helicenes: Syntheses, (Anti)Aromaticity and Properties

N-Annulated [5]helicene (NH5) and its dibenzo-extended derivatives are synthesized by cycloisomerization and Scholl-type cyclodehydrogenation methods, respectively. Nitrogen-bridging of fjord-carbons 1 and 14 of [5]helicene endows saddle-like NH5 featuring an antiaromatic azepine core with enhanced orbital overlap between nitrogen and the carbon π-system. N-Annulation results in less stabilized HOMO, a smaller HOMO-LUMO energy gap, red-shifted absorption, fluorescence, paratropic ring current over the azepine unit, and tunable aromaticity of the core relative to pristine [5]helicene. The NH5 derivatives exhibit space-charge-limited current hole mobility on the order of 10^-3 cm² V^-1 s^-1, which is higher than that of N-annulated PAH, like N-annulated perylene.