Molecular Spiral Staircases: Stepwise Construction of Multilayer Phenylene Stacks

Stacked aromatic architectures represent important structural motifs in supramolecular chemistry, materials science, and molecular recognition. Herein, we report the modular synthesis of a series of covalently linked phenylene stacks containing up to six stacked phenylene units through consecutive Friedländer annulation reactions. The key structural motif is a bay-substituted 6,7-dihydrodibenzo[b,j][4,7]phenanthroline (DHDBPT) scaffold, which enforces close face-to-face arrangements between phenylene units. The resulting staircase-like architectures were characterized by spectroscopic techniques and single-crystal X-ray diffraction. Structural investigations further demonstrated distinct stereochemical behavior across the oligomer series. Odd-layer systems adopt meso configurations, whereas even-layer oligomers exhibit C2 chirality and can be resolved. The rotational barriers of terminal phenyl groups were shown to increase with stack thickness, suggesting increasing cooperative rigidity within the densely packed aromatic framework.