Synthesis of a Tetracene‐Based Helicene

Chiral tetracene‐based π‐systems have remained largely unexplored. Herein, we report the synthesis of a tetracene‐based nor[6]helicene from 5‐(phenanthren‐4‐yl)tetracene wherein parent tetracene is fused with phenanthrene through a pentagon. The electron‐deficient character of the pentagonal ring consequently imparts a considerably narrowed HOMO–LUMO gap, leading to absorption edge found at 670 nm. The optical resolution of the tetracene‐based nor[6]helicene gave two enantiomers showing mirror‐image Cotton effects reaching to 650 nm. The largest absorption dissymmetry factor was recorded to be | g _CD | = 6.0 × 10 ^–3 at 316 nm. According to theoretical calculations, this molecule possesses the relatively large magnetic transition dipole moments in most vertical transitions on the ground of peripheral distribution of the electron densities engaged in the magnetic term of the transition dipole moments.