Optimization of Naphtho[2,3-b]thiophene diimide-Based Triads with Varying π-Bridge Structures for Enhanced Charge Transport

A deep understanding of the relationship between material structure and performance is essential for the advancement of high-performance n-type organic semiconductor materials. This study investigates the design of NTI-based triads, focusing on how varying π-bridge structures affect their electronic properties and charge transport in organic field-effect transistors (OFETs). Four triads—NTI-Tz-NTI, NTI-BTTz-NTI, NTI-BBTdz-NTI, and NTI-BBTz-NTI—were synthesized by incorporating electron-deficient π-bridges with different conjugation lengths, aimed at optimizing molecular planarity and lowering the lowest unoccupied molecular orbital (LUMO) energy, crucial for improving n-type charge transport. The study systematically evaluated the effects of these structural variations on charge transport, thermal stability, and optoelectronic properties. NTI-BTTz-NTI and NTI-BBTz-NTI, with longer conjugated π-bridges, showed an increase of more than one order of magnitude increase in electron mobility compared to NTI-Tz-NTI and NTI-BBTdz-NTI, with NTI-BTTz-NTI achieving the highest mobility of 0.056 cm ² V ^-1 s ^-1 . X-ray diffraction (XRD) and atomic force microscopy (AFM) analysis revealed highly ordered molecular packing and strong π-π stacking interactions in NTI-BTTz-NTI, enhancing charge transport. These findings underscore the importance of molecular structure and packing morphology in optimizing OFET performance, providing a framework for designing high-performance n-type organic semiconductors for efficient and stable organic electronic devices.