Insights into the molecular self-assembly of urea-functionalized acetylenes

Abstract This study investigates simple acetylenes substituted with phenylurea as a constant H-bonding unit (Alk-R) and varied hydrophobic units (R = H, Phenyl (Ph), phenylacetylene (PA), Ph-NMe₂) to understand self-assembly properties driven by synergistic non-covalent interactions. Our observations reveal hierarchical self-assembled fibrillar networks with luminescent needles, fibers, and flowers on nano- to micro-meter scales. Subtle changes in substituents led to significant differences: H, Ph, PA, and Ph-NMe₂ produced needle-like crystals, dendritic nanofibers, microflakes, and no self-assembly, respectively. Alk-Ph-NMe₂ likely did not self-assemble due to reduced hydrophobic interactions and steric hindrance. Interestingly, Alk-Ph exhibited a uniform spherulitic pattern and effectively gelled organic solvents and water. This luminescent gel demonstrated multifunctionality, including white light emission when doped with rhodamine-B dye and adsorption of organic cationic dyes (methylene blue and crystal violet) from water. This study offers valuable insights into balancing interactions to achieve desired hierarchical networks and understand material properties, guiding future molecular design.