H-Bonding Control of Supramolecular Ordering of Diketopyrrolopyrroles

Diketopyrrolopyrrole (DPP) is a widely used building block for high-mobility ambipolar semiconductors. Hydrogen bonding of N-unsubstituted DPPs has recently been identified as a tool for controlling their solid state structure and properties of semiconducting films, yet little is known about supramolecular packing of H-bonded DPP derivatives. Here we report a comparative study of three archetypical DPP derivatives, difurylDPP (DFDPP), diphenylDPP (DPDPP), and dithienylDPP (DTDPP), at the interface and in bulk crystals. Using scanning tunneling microscopy (STM) combined with X-ray crystallographic analysis, we demonstrate how the interactions of the (hetero)aromatic substituents interplay with H-bonding, causing dramatic differences in the supramolecular ordering of these structurally similar building blocks. Under all explored conditions, DPDPP exclusively forms H-bonded homoassemblies; DFDPP strongly prefers to co-assemble with alkanoic acids, through a rare lactam···carboxylic acid H-bonded complex, and DTDPP, depending on conditions, either co-assembles with alkanoic acids or self-assembles in one of two H-bonded polymorphs. One of these polymorphs suggests an out-of-plane twist of thiophene rings that form π-stacks running along the surface plane; this is unexpected considering the large energetic penalty of DTDPP deplanarization. The results are explained in terms of inter- versus intramolecular interactions, which are quantified with density functional theory calculations. This work shows that aryl substituents can strongly influence H-bonding assembly of DPP derivatives that is likely to affect their charge-transport properties.