Organic semiconductors emerge as promising chemiresistive gas-sensing materials, benefiting from their high selectivity and sensitivity toward various gases. However, these materials usually work at room temperature; thus, the adsorption of water vapor is usually unavoidable and produces interfering signals, which significantly hinders the detection of nitric dioxide (NO2) at the parts per billion (ppb) level and their practical application. In this work, side-chain engineering was applied to ion-in-conjugation (IIC) polymers for addressing moisture interference in NO2 sensing. By controlling the condensing precursors, different numbers of methyl groups (n = 0/1/2) were introduced on the phenyl ring. The side-chain engineering could enable the polymers to stably detect NO2 even at relative humidity levels ranging from 0 to 75% at the parts per billion level. Specifically, the p-PTS (n = 1)-based sensor shows only a 10.3% decrease in response to NO2 at room temperature without requiring heating or hydrophobic layer coverage. Moreover, these polymers demonstrate the highest charge transfer after adsorbing NO2 compared to other interfering gases, which endow the sensors with high selectivity for NO2. Theoretical calculations reveal that the introduction of methyl groups improves the planarity of the polymer backbone upon water adsorption, which enhances the charge transfer following NO2 adsorption. At the same time, the presence of methyl groups prevents water molecules from accessing the adsorption sites and provides an inherent moisture resistance. These results offer an approach for creating high-performance NO2 sensors with built-in moisture resistance and establish a foundation for future use in more challenging environmental conditions.
Wang et al. (2026) studied this question.