Isomeric Column‐Forming Esters and Imides with Varying Curvatures of the Aromatic Plane

AbstractDibenzo[a,j]coronene‐tetracarboxylic alkyl esters and imides with either a centrosymmetric bis‐peri substitution pattern or a polar bis‐ortho substitution pattern form hexagonal columnar mesophases, which in the case of the imides persist at room temperature. The bis‐peri isomers are obtained via a two‐fold oxidative photocyclization; the bis‐ortho isomers are accessed via a glyoxylic Perkin reaction of triphenylene and naphthalene building blocks. Steric congestion between the substituents and the adjacent benzo protrusion in the bis‐ortho esters and imides leads to bending of the aromatic plane, which thus avoids twisting. These isomers surprisingly show a more pronounced liquid crystalline behaviour than their non‐bent bis‐peri homologs, accommodating non‐planarity with columnar order by slipped stacking. Whereas both types of ester and the bis‐peri imide show an optical behaviour typical for perylene chromophores, the strongly bent bis‐ortho imide distinguishes itself notably from them by its absorption spectrum. The electron acceptor strength of the isomeric diimides is found to differ, the hexagonal (peri) diimide having a 0.20 eV lower LUMO energy than the pentagonal (ortho) isomer.