Supramolecular Polymorphism of the Hydrogen-Bonded C₃-Symmetrical Hexadehydrotribenzo[12]annulene Derivative

The C₃-symmetric hexadehydrotribenzo[12]annulene ([12]DBA) derivative (1a) with three tetradecylamide (-NHCOC₁₄H₂₉) chains capable of hydrogen-bonding interaction formed either a two-dimensional lamellar (LM) or a one-dimensional (1D) nanofiber (NF) molecular assembly, depending on the association state of the amide hydrogen bonds in the solution phase. The intermolecular amide hydrogen-bonding modes in the LM and NF structures were different from each other. The NF structure was metastable, 2.2 kJ mol^-1 less stable than that of the LM structure, and was obtained through organogel formation. In CHCl₃, 1a exhibited a 1D association behavior following the isodesmic model (K = 2.18 × 10³ M^-1) due to intermolecular amide hydrogen bonds, whereas the presence of CH₃CN inhibited this association state. The NF structure had larger amplitude dynamics about the polar amide group than that of the LM structure, undergoing a phase transition from the NF to the LM structure upon heating. The absorption spectra of NF and solid-state LM were different from each other, exhibiting different optical properties. The coexistence of intermolecular amide hydrogen bonds and van der Waals interactions among the C₃-symmetric molecules resulted in polymorphic phenomena, where energetically similar molecular assemblies were expressed.