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.
Dedicated to Professor Klaus Müllen on the occasion of his 75th birthday.Curved graphene nanoribbons (GNRs) with hybrid edge structures have recently attracted increasing attention due to their unique band structures and electronic properties as a result of their nonplanar conformation. This work reports the solution synthesis of a long and curved multi-edged GNR (cMGNR) with unprecedented cove-armchair-gulf edge structures. The synthesis involves an efficient A 2 B 2 -type Diels-Alder polymerization between a diethynyl-substituted prefused bichrysene monomer (3b) and a dicyclopenta[e,l]pyrene-5,11-dione derivative (6) followed by FeCl 3 -mediated Scholl oxidative cyclodehydrogenation of the obtained polyarylenes (P1). Model compounds 1a and 1b are first synthesized to examine the suitability and efficiency of the corresponding polymers for the Scholl reaction. The successful formation of cMGNR from polymer P1 bearing prefused bichrysene units is confirmed by FTIR, Raman, and solid-state NMR analyses. The cove-edge structure of the cMGNR imparts the ribbon with a unique nonplanar conformation as revealed by density functional theory (DFT) simulation, which effectively enhances its dispersibility in solution. The cMGNR has a narrow optical bandgap of 1.61 eV, as estimated from the UV-vis absorption spectrum, which is among the family of low-bandgap solution-synthesized GNRs. Moreover, the cMGNR exhibits a carrier mobility of ≈2 cm 2 V −1 s −1 inferred from contact-free terahertz spectroscopy.
The lithiation mechanism of tin nanoparticle-based negative electrodes is reported and systematically studied via operando 7 Li nuclear magnetic resonance (NMR) and X-ray diffraction (XRD) combined with ex situ 119 Sn magic-angle spinning (MAS) NMR. Besides the formation of the Sn-rich phases Li 2 Sn 5 and LiSn, also the Li-richer phase Li 7 Sn 3 is observed in good agreement with the structural evolution of the binary Li−Sn phase diagram. However, the structural investigations using ex situ 119 Sn MAS NMR clearly reveal the formation of a disordered Li x Sn phase with increasing lithiation, possessing the structural fingerprints of Li 7 Sn 3 with no longrange order and a body-centered cubic (bcc) packing of Sn (from XRD). Thus, in contrast to previous studies relying on 7 Li NMR only, the formation of any of the Li-rich bulk crystalline Li−Sn phases
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