Boosting Carrier Mobility in Novel Naphthodithiophene Diimide (NDTI)-Based Triad Through π-Conjugation Expansion

Enhancing the length of π-conjugation in molecules represents an efficient strategy for fine-tuning the optoelectronic characteristics of organic semiconductors. Nevertheless, this approach is infrequently conducted for small molecules with n-type properties. Herein, we report the design and synthesis of a novel naphthodithiophene diimide (NDTI)-based small-molecule semiconductor, NDTI-BBTE, featuring a long benzo[b]thiophen-2-ylethynyl (BTE) end cap. NDTI-BBTE exhibits good solubility in some common organic solvents and a LUMO energy level of −4.15 eV, promoting stable electron transport in ambient conditions. Compared to our previously reported NDTI-BET with a thiophenylethynyl end cap, NDTI-BBTE shows improved device performance, achieving a maximum electron mobility of 0.052 cm² V⁻¹ s⁻¹ under identical conditions. The XRD and AFM measurements reveal that NDTI-BBTE has lower d-spacing and higher crystallinity than NDTI-BTE. These results demonstrate that increasing π-conjugation length of the molecules is a simple and effective strategy for designing solution-processable, air-stable n-type organic semiconductors for printed electronics.