Halogen-Bonding-Steered Thermal Reassembly into Brickwork Packing Motifs Enhances Electron Transport in Naphthalenediimides.

Electron transport in organic semiconductor solids with high carrier mobility is crucial for the realization of high-performance organic electronic devices. In molecular semiconductors, self-assembly pathways and the resulting supramolecular superstructures play a decisive role in dictating the molecular packing, which in turn governs charge-transport efficiency. Therefore, weak noncovalent interactions must be carefully engineered to fine-tune molecular stacking motifs. Herein, we investigate the role of halogen-bonded intermolecular interactions in directing naphthalenediimide (NDI) stacks toward temperature-induced realignment, leading to robust brickwork-type molecular assemblies in both thin films and solids. This structural reorganization significantly influences their optical properties and electron transport characteristics. In core-unsubstituted NDI derivatives, assembly is typically governed by hydrogen-bond-driven in-plane interactions, resulting in slipped one-dimensional columnar stacks. In contrast, brominated NDI cores promote halogen-bond-mediated organization, yielding efficient brickwork stacking motifs, either in their pristine state or after thermal realignment, depending on the end-group substitution. In summary, hydrogen-bond-dominated assembly pathways tend to produce poorly stacked domains with limited charge-transport efficiency, whereas halogen-bond-driven pathways generate well-ordered brickwork assemblies that facilitate superior electron mobility. To substantiate these findings, we performed comprehensive optical measurements, grazing incidence wide angle X-ray scattering (GIWAXS) analysis, and electrical characterization of organic field-effect transistors (OFETs).