Computational Studies of Self-assembling Squaramide and Urea Derivatives

Computational quantum chemical tools were applied to investigate important driving forces underlying the monomer self-assembly of squaramide and urea synthons to form supermolecular polymers. The roles of noncovalent interactions, such as hydrogen bonding and π-stacking, also were examined. Computed results suggest that replacing oxygen by sulfur in squaramide and urea synthons resulted in drastically different self-assembly arrangements of the synthons; oxo derivatives prefer linear hydrogen bonded arrangements while thio derivatives prefer stacked arrangements. Geometric, energetic, and magnetic criteria of aromaticity were employed to investigate the effects of aromaticity gain in the assembled synthons. Computed results show that the aromatic character of squaramide synthons increased through hydrogen bonded self-assembly, and suggest that aromaticity gain should be considered in the molecular designs of self-assembling monomers for supramolecular chemistry.