Unraveling Quantitative Sensing Mechanism and Predictive Molecular Metrics for High‐Performance OFET Amine Sensors

Abstract Sensitive and selective detection of volatile amines has seen growing interest in the past few years due to the applications it has in food quality control, medical diagnosis, and environmental protection. Metal organic hybrid materials such as phthalocyanines have emerged as promising sensing materials due to their high sensing performance at ambient conditions, solution processibility, and lightweight, flexible form factors. Herein, the amine sensing capabilities of a composite system consisting of chloro boron subphthalocyanine and isoindigo bithiophene polymer are demonstrated, achieving a limit of detection of 0.005 part per billion (ppb) for ammonia while maintaining high selectivity against analogues at room temperature. To quantitatively describe the sensing mechanism and the effect of introducing the metal organic compound, the data are modeled using the Freundlich isotherm, which reveals the presence of multiple sensing regimes and heterogeneity in surface adsorption of amines. Meaningful trends are experimentally shown between the sensor's performance to different amines, and their respective molecular volumes and Lewis basicity. These trends are built upon by proposing an equation inspired by Polanyi adsorption theory that can theoretically predict the sensor's performance to a given amine and subsequently derive a new theoretical term which represents the intrinsic binding affinity of the material system.