Air-Stable n‑Type Organic Field-Effect Transistors Based on 4,9-Dihydro‑s‑indaceno[1,2‑b:5,6‑b′]dithiazole-4,9-dione Unit

4,9-Dihydro-s-indaceno­[1,2-b:5,6-b′]­dithiazole-4,9-dione (IDD) was designed as a novel electronegative unit, and the π-conjugated compound (2C-TzPhTz) containing it was synthesized as a candidate for air-stable n-type organic field-effect transistor (OFET) materials. Cyclic voltammetry measurements revealed that the IDD unit contributes to lowering the lowest unoccupied molecular orbital (LUMO) energy level. X-ray crystallographic analysis of 2C-TzPhTz showed an almost planar molecular geometry and dense molecular packing, which is advantageous to electron transport. OFETs based on 2C-TzPhTz showed high electron mobility of up to 0.39 cm2 V–1 s–1, which is one of the highest electron mobilities observed among pentacyclic dione-based materials. Top-contact OFET devices showed operating stability and long-term stability under ambient conditions, attributed to the low-lying LUMO energy level and dense packing in the solid state. Furthermore, bottom-contact OFETs also maintained good electron mobility beyond 0.1 cm2 V–1 s–1 under air-exposed conditions. We demonstrated that n-type OFETs are more sensitive to H2O than O2 and found that the acquirement of air stability for the 2C-TzPhTz-based OFET is due to the increased stability against not only O2 but also H2O. All of these results indicate that IDD is a potentially useful building unit for high-performance air-stable n-type semiconducting materials.