Impact of Molecular Structure on Self-Assembly Morphology: A Comparative Study of V-Shaped and U-Shaped Bis(biphenyl)ureas

Analysis based on single crystal structures of V-shaped and U-shaped urea derivatives revealed that the spatial relationship between the urea hydrogen-bonding axis and the biphenyl axis plays a critical role in governing molecular packing. The V-shaped urea derivative adopts a skewed orientation of the biphenyl moieties relative to the urea hydrogen-bonding axis, which is assumed to allow rotational freedom of the biphenyl units in the formed molecular aggregates and to facilitate strong phenyl–phenyl interactions when the aggregates approach each other in an antiparallel manner. This results in the formation of a densely packed three-dimensional network. In contrast, the U-shaped urea derivative arranges its biphenyl moieties parallel to the urea hydrogen-bonding axis in the formed one-dimensional molecular aggregates, where steric hindrance limits biphenyl rotation and hinders effective interaggregate phenyl–phenyl interactions, presumably resulting in a weakly packed antiparallel assembly of these one-dimensional structures. These findings demonstrate that both the overall molecular shape and the conformational flexibility of its components play a highly important role in constructing supramolecular architecture, providing a guiding principle for designing organic crystals with specific packing patterns and desired properties.