Naphtho[2,3-b]thiophene diimide-terminated acceptor triads for improved n-type organic semiconductors
The development of high-performance n-type organic semiconductors is critical for advancing organic field-effect transistors (OFETs) and p-n complementary logic circuits. This study reports two novel n-type triple-acceptor triads, NTI-BTT and NTI-BT, based on naphtho[2,3-b]thiophene diimide (NTI), a monothiophene-extended naphthalene diimide (NDI). The influence of thiophene fusion versus spacer insertion on physicochemical and charge transport properties is systematically investigated. NTI-terminated triads exhibit enhanced electron-withdrawing capabilities, deeper energy levels, and more planar backbones compared to NDI-based counterparts. However, NTI-BT-based OFETs suffer a substantial drop in electron mobility to 0.004 cm2 V−1 s−1 due to polycrystalline structure with multiple grain boundaries that increase trap state density. In contrast, introducing thiophene spacers between NTI and benzothiadiazole units in NTI-BTT effectively enhances n-type charge transport by improving π-π interactions and reducing intermolecular distances, achieving a short π-π stacking distance of 3.45 Å. Consequently, NTI-BTT exhibits a significantly improved electron mobility of 0.13 cm2 V−1 s−1, four times higher than the NDI-based counterpart. These findings provide valuable insights into molecular design principles for high-performance n-type organic semiconductors, highlighting the impact of molecular structure and intermolecular interactions on charge transport.