Influence of Hydrogen Bonds on the Supramolecular Order of Hexa-peri-hexabenzocoronenes

Three different hexa‐peri‐hexabenzocoronene (HBC) derivatives with carboxylic acid functions have been synthesized to study the effect of hydrogen bonding on the already pronounced columnar π‐stacking. This functionalization improves the degree of order in the bulk and influences the surface patterning at solid‐liquid interfaces as well as the thermal properties of these materials. The length of the tether between the aromatic core and the hydrogen‐bond‐forming carboxy group appears as a key factor influencing the supramolecular self‐assembly, since only the HBCs with shorter spacers showed a strong synergetic effect of the columnar π‐stacking with the hydrogen‐bonding motifs. Clear signatures for this are unusually high mesophase transition temperatures and non‐tilted columnar stacking in the pseudocrystalline phase. As model systems, HBC dyads have been synthesized with the two HBC disks linked through a covalent spacer fitting the intercolumnar distance of the short‐tethered, hydrogen‐bridged dimer. This comparison emphasized the impact of the hydrogen bonds on the supramolecular properties of the materials. A broad range of analytical methods have been used, including differential scanning calorimetry, wide‐angle X‐ray diffractometry, solid‐state NMR spectroscopy, and scanning tunneling microscopy. Addition of hydrogen‐bonding motifs to the periphery of hexa‐peri‐hexabenzocoronenes has been carried out in order to study the effect of hydrogen bonding on the already pronounced columnar π‐stacking (see Figure). The thermal properties as well as the supramolecular order of the materials can be improved; such improvement is a prerequisite for successful implementation in electronic devices.