Hydrogen Bonds Control Single-Chain Conformation, Crystallinity, and Electron Transport in Isoelectronic Diketopyrrolopyrrole Copolymers

The combination of computational methods and advanced characterization techniques is used to highlight the role of the intramolecular hydrogen bond in thienyldiketopyrrolopyrrole (ThDPPTh) copolymerized with tetrafluorobenzene (F4) to PThDPPThF4. We investigate how the torsion potentials of ThDPPTh and isoelectronic dithiazolyldiketopyrrolopyrrole (TzDPPTz) are influenced by hydrogen bonding and translate into different conformation, molecular, structural, and opto-electronic characteristics. ThDPPTh exhibits N,S-syn orientation in the most stable conformer locked by an intramolecular hydrogen bond. In TzDPPTz, such a hydrogen bond is not possible, which leads to a “ring flip” and makes the N,S-anti conformer most stable. Copolymers with F4, PThDPPThF4 and PTzDPPTzF4, exhibit straight and curved backbones, respectively, but similar chain rigidity. These conformations are experimentally confirmed by local packing motifs from solid-state NMR spectroscopy. The differences in conformation strongly influence the opto-electronic and structural properties. X-ray scattering and atomic force microscopy reveal lamellar morphologies of both PThDPPThF4 and PTzDPPTzF4, but increased long range order, reduced paracrystallinity, and larger domains of the former. In-depth analysis of solid-state NMR spectra allows for obtaining information on absolute degrees of crystallinity, which are substantially higher for PThDPPThF4. These differences in structural properties cause field-effect electron mobilities of PThDPPThF4 to be larger by a factor of 20.