Strategic Approach for Enhancing Sensitivity of Ammonia Gas Detection: Molecular Design Rule and Morphology Optimization for Stable Radical Anion Formation of Rylene Diimide Semiconductors

Herein, a strategic approach to enhance the sensitivity of ammonia gas detection using organic semiconductors by boosting the efficiency of ammonia gas‐induced stable radical anion formation (SRAF) is reported. This is achieved through rational molecular design and engineering of field‐effect transistors (FETs). New rylene diimide derivatives are designed and used to prepare molecular templates for efficient SRAF in thin films, and they are applied as gas‐adsorbing active layers in FETs. Substituting linear‐shaped perfluoroalkyl (PF) groups to π‐electron‐deficient naphthalene diimide (NDI) backbone enhances the ammonia gas detection limit to 200 ppb, attributed to the strong electron‐withdrawing capability and low steric hindrance of PF groups. Replacing the core backbone (NDI) with perylene diimide (PDI) while retaining the PF group further enhances gas‐responsivity up to 18.17 (1700% increase in current) due to the enlarged π‐conjugated bridge area. Computational characterization further supports that high electron affinity of the PDI‐PF molecules and a larger gas‐adsorption area in the PDI core result in the exceptional ammonia gas sensitivity. In addition, beneficial molecular orientation and nanopore formation of PDI‐PF facilitate gas adsorption, resulting in remarkably enhanced gas‐responsivity. The results indicate that molecular engineering for high‐efficiency SRAF suggests a new strategy for developing high‐sensitivity ammonia sensing platforms. A strategic approach to enhance the sensitivity of ammonia gas detection using n‐type organic semiconductor thin film is developed by boosting the efficiency of ammonia‐gas‐induced stable radical anion formation, which enables simultaneous achievement of excellent gas‐responsivity and detection limit.