Influence of Backbone Chlorination on the Electronic Properties of Diketopyrrolopyrrole (DPP)‐Based Dimers

Abstract

Chlorination of π‐conjugated backbones is garnering great interest because of fine‐tuning electronic properties of conjugated materials for organic devices. Herein we report a synthesis of thiophene‐based diketopyrrolopyrrole (DPP) dimers and their chlorinated counterparts by introducing a chlorine atom in the outer thiophene ring to investigate the influence of the chlorination on charge transport. The backbone chlorination lowers both the HOMO and the LUMO of the dimers and leads to a blue‐shift of maximum absorption in compared to unsubstituted counterparts. X‐ray analysis reveals that the chlorine atom prompts the outer thiophene ring out of the planarity of the backbone with a relatively large torsional angle. The chlorinated dimers exhibit slipped one‐dimensional packing decorated with multiple intermolecular interactions, because of a combination of a negative inductive effect and a positive mesomeric effect of the halogen atom, which might facilitate charge transport within the oligomeric backbones. The mobility in the single‐crystal OFET devices of the chlorinated dimers is up to 1.5 cm2 V−1 s−1, which is two times higher than that of the non‐chlorinated DPP dimers. Our results indicate that the chlorine atom plays a key role in directing non‐covalent interactions to lock the slipped stacks, enabling electronic coupling between adjacent molecules for efficient charge transport. In addition, our results also demonstrate that these DPP dimers with straight n‐octyl chains exhibit higher mobilities than the dimers with branched 2‐ethylhexyl chains.

Crystal Engineering of Angular-Shaped Heteroarenes Based on Cyclopenta[b]thiopyran for Controlling the Charge Carrier Mobility

“…The shortest S···H contact distances of C 4 -SS , C 6 -SS , C 8 -SS , and C 10 -SS are 3.13, 2.91, 3.15, and 3.13 Å, respectively (Figures a–d). Moreover, the halogen substituents on oligoacenes have been reported to facilitate cofacial π–π stacking of aromatic systems due to the halogen-induced intermolecular interactions . Upon the introduction of chlorides at the 2-, 3-, and 4-positions of the thiopyran rings of C 8 -SS , intermolecular C–Cl···H–C interactions can be found for all the three chlorinated heteroarenes.…”

“…Moreover, the halogen substituents on oligoacenes have been reported to facilitate cofacial π−π stacking of aromatic systems due to the halogeninduced intermolecular interactions. 48 contact interactions, which may facilitate the denser and tighter packing of the chlorinated heteroarene molecules. Figure 6 displays the molecular packing structures in the obtained 10 single crystals for the angular-shaped heteroarenes based on cyclopenta[b]thiopyran.…”

Polymorphism of a semi‐crystalline diketopyrrolopyrrole‐terthiophene polymer

“…[15] To learn more about the structural molecular parameters that induce or influence polymorphism in PDPPnT polymers, we here investigate the corresponding PDPP3T polymer with a terthiophene (3T) conjugated segment in the main chain instead of 4T (Figure 1). Assuming that adjacent thiophenes adopt an s-trans conformation, [25,26] the relative orientation of the DPP units along the main chain then changes from parallel in PDPP4T to an alternating (right-left) orientation in PDPP3T as a consequence of the odd number of thiophene rings in the repeat unit of PDPP3T (Figure 2). This then leads to alternating large and small separations between the linear alkyl chains and at the same time the branched alkyl chains no longer have an anti orientation, [17] but would be present in syn oriented pairs.…”

Synthesis and Optoelectronic Properties of New Methoxy-Substituted Diketopyrrolopyrrole Polymers

“…15 Only recently has the derivatization of the 4-position of the flanking thiophenes of the DPP unit with functional groups of varying electron densities taken hold as an avenue for exploration in polymer systems. 26−31 Of the derivatives synthesized, most involve a σ/π-withdrawing group, including −F, −Cl, −CN, whereas the only other derivative imparts a slightly donating −Me. All of these showed optical and electrochemical E g changes attributed to the newly imparted functional group.…”

“…Thiophenes, thereby, allow for planar configurations with longer effective conjugation and smaller π–π-stacking distances to effectively modulate the electrochemical and optical band-gaps ( E g ) of polymers. − Other strategies include the incorporation of various solubilizing sidechains, − the modification of polymer backbones, , favorable D–A co-monomer matching, and donor unit modification . Only recently has the derivatization of the 4-position of the flanking thiophenes of the DPP unit with functional groups of varying electron densities taken hold as an avenue for exploration in polymer systems. − Of the derivatives synthesized, most involve a σ/π-withdrawing group, including −F, −Cl, −CN, whereas the only other derivative imparts a slightly donating −Me. All of these showed optical and electrochemical E g changes attributed to the newly imparted functional group.…”