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

<i>N</i>-Annulated [5]helicene (<b>NH5</b>) and its dibenzo-extended derivatives are synthesized by cycloisomerization and Scholl-type cyclodehydrogenation methods, respectively. Nitrogen-bridging of <i>fjord</i>-carbons 1 and 14 of [5]helicene endows saddle-like <b>NH5</b> featuring an antiaromatic azepine core with enhanced orbital overlap between nitrogen and the carbon π-system. <i>N</i>-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 <b>NH5</b> 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 <i>N</i>-annulated PAH, like <i>N</i>-annulated perylene.