Supramolecular Polymorphism of the Hydrogen-Bonded <i>C</i>₃-Symmetrical Hexadehydrotribenzo[12]annulene Derivative

The <i>C</i>₃-symmetric hexadehydrotribenzo[12]annulene (<b>[12]DBA</b>) derivative (<b>1a</b>) with three tetradecylamide (-NHCOC₁₄H₂₉) chains capable of hydrogen-bonding interaction formed either a two-dimensional lamellar (<b>LM</b>) or a one-dimensional (1D) nanofiber (<b>NF</b>) molecular assembly, depending on the association state of the amide hydrogen bonds in the solution phase. The intermolecular amide hydrogen-bonding modes in the <b>LM</b> and <b>NF</b> structures were different from each other. The <b>NF</b> structure was metastable, 2.2 kJ mol^-1 less stable than that of the <b>LM</b> structure, and was obtained through organogel formation. In CHCl₃, <b>1a</b> exhibited a 1D association behavior following the isodesmic model (<i>K</i> = 2.18 × 10³ M^-1) due to intermolecular amide hydrogen bonds, whereas the presence of CH₃CN inhibited this association state. The <b>NF</b> structure had larger amplitude dynamics about the polar amide group than that of the <b>LM</b> structure, undergoing a phase transition from the <b>NF</b> to the <b>LM</b> structure upon heating. The absorption spectra of <b>NF</b> and solid-state <b>LM</b> were different from each other, exhibiting different optical properties. The coexistence of intermolecular amide hydrogen bonds and van der Waals interactions among the <i>C</i>₃-symmetric molecules resulted in polymorphic phenomena, where energetically similar molecular assemblies were expressed.