Investigation of gas sensing properties of organic π–π* complexes spin coated thin films in dry and humid environment

Exposure to gaseous pollutants in both enclosed and open environments poses a significant risk to human health. In this study, an optical detection-based sensor was developed for the selective detection of toxic ammonia gas in the environment at low concentrations. Three newly synthesized organic π–π* charge-transfer (CT) complexes—anthracene picrate (ANTPc), phenanthrene picrate (PHENPc), and pyrene picrate (PYRPc)—obtained from polynuclear aromatic hydrocarbons and picric acid precursors (ANTP, PHENP, and PYRP, respectively), were evaluated for the first time as sensing thin film materials in gas sensor applications. These complexes were transferred as thin films onto the substrates using the spin-coating method for structural characterization and investigation of their sensor properties. The sensor analyses were conducted using the surface plasmon resonance (SPR) method. It was observed that the PHENPc-, ANTPc-, and PRYPc-based thin film sensors were highly selective to ammonia with the sensitivity values of 0.00007, 0.0003, and 0.0017 ppm⁻¹, respectively. Although they are very similar to each other in terms of chemical structure, the thin film sensors produced from these three materials exhibited different responses to the vapors at room temperature. In the last section of the study, repeated gas detection measurements conducted under varying humidity conditions demonstrated that humidity affects the sensitivity of the sensors.