A small library of ureas and related compounds was synthesized and examined by scanning electron microscopy (SEM), single-crystal X-ray diffraction, powder X-ray (pXRD), and polarized optical microscopy (POM) techniques in order to elucidate the factors controlling their self-assembly in the solid state. Inspection of the 12 solid-state structures revealed that molecules in the crystal lattice are held together by intermolecular H-bonding, π-π stacking as well as C-H/p interactions. The same interactions are likely responsible for the formation of supramolecular aggregates (e.g. sheet-like assemblies, micro- and nano-fibers, and the porous networks easily identifiable by SEM technique) and in certain cases led to the small molecules gelation. [ABSTRACT FROM AUTHOR]