Naphthobispyrazine Bisimide: A Strong Acceptor Unit for Conjugated Polymers Enabling Highly Coplanar Backbone, Short π–π Stacking, and High Electron Transport

Abstract

The development of acceptor units that ensure high electron transport in π-conjugated polymers is imperative to advance the field of printable electronics. We have designed and synthesized naphthobispyrazine bisimide (NPI) as a novel strong acceptor unit by chemical conversion from naphthobispyrazine tetraester (NPE). We have also synthesized NPI-based polymers using bithiophene derivatives with and without fluorine groups as co-monomers. Notably, the NPI polymer-based transistors demonstrated ambipolar characteristics with hole and electron mobilities of up to 0.8 and 0.7 cm2 V–1 s–1, respectively, despite the unfavorable face-on orientation, and those values were more than 2 orders of magnitude higher than the hole and electron mobilities of their NPE counterpart. We ascribed the greatly enhanced mobilities to the highly coplanar and rigid backbone and the quite high crystallinity along with the short π–π stacking distances of the order of 3.4 Å, which resulted in efficient intra- and interchain charge carrier transport. We also found that the fluorine atom can act as a conformation-directing group, depending on the substitution position, which led to a more regular backbone structure with reduced energetic disorder while achieving higher solubility. We showed that NPI is a promising acceptor unit for high-performance electron-transporting π-conjugated polymers.

Non-covalent interactions (NCIs) in π-conjugated functional materials: advances and perspectives

“…Indeed, the enhanced performance could be attributed to the greater extent of inter and intramolecular NCIs and regular backbone. 103…”

Electron-Transporting Conjugated Polymers from Novel Aromatic Five-Membered Diimides: Naphtho[1,2-b:4,3-b′]-dithiophene and -Diselenophene Diimides

“…Imide-functionalized arenes − such as pyromellitic, , perylene, , and naphthalene , diimides are regarded as the important building blocks in the design and synthesis of polymeric engineering materials, intense organic chromophores, , and organic/polymeric semiconductors. , For example, Kapton is a well-known imide-functionalized polymeric engineering material with excellent mechanical properties and high temperature resistance . The utilization of these species in donor–acceptor (D–A)-conjugated polymers has also received increasing attention during the past few decades owing to their high electron deficiencies, desirable optoelectronic properties, high carrier mobilities, as well as fine-tunable solubility and solid-state packing via imide N -alkylation .…”

Carboxamide and carbamate substituted π-conjugated polymers: the effect of hydrogen bonding on photovoltaic properties

“…7 Recently, noncovalent intramolecular interactions were employed to increase the torsional barrier, thereby enhancing coplanarity. [8][9][10][11] The binding energies of the noncovalent interactions such as S⋯X and C-H⋯X (X = O, N, F) are usually small (in the range of 0.44-2.20 kcal mol −1 ). 7 However, their existence significantly improves the semiconducting properties of many conjugated polymers.…”