Thermal Desorption of Explosives Vapour from Organic Fluorescent Sensors

Organic semiconductors can be used as highly sensitive fluorescent sensors for the detection of nitroaromatic explosives such as TNT. When trace-level vapours of explosives encounter an organic fluorescent sensor, molecules from the vapour are absorbed into the film and modify the light-emitting properties. Specifically, an electron is transferred from a photogenerated exciton in the sensor to a sorbed nitroaromatic molecule which results in fluorescence quenching and indicates the presence of explosives in the surrounding environment. The response to ppb levels of explosives is very rapid, however for many organic fluorescent sensors, the quenching of fluorescence is irreversible which make them single use sensors, and imposes a limitation in terms of reusability of the sensors. Here, we present a study of thermal desorption of 2,4-DNT from thin film explosives sensors made from the commercial fluorescent polymer, Super Yellow. Thermal cycling of the sensor results in recovery of fluorescence thereby making them reusable, and providing a route to confirm that fluorescence quenching arises from analyte response. To optimise the sensors performance in terms of reusability, Super Yellow sensors, and blend of Super Yellow/Poly carbazole (PVK) sensors were fabricated. The sensors were exposed to 2,4-DNT vapour in a custom-made chamber while monitoring their fluorescence, and then heated to an optimum desorption temperature to desorb the DNT molecules from the sensors. Finally, the improvement of the sensors made from the polymer blend, and the effect of temperature on the sensors is discussed. This method can be applied to other organic fluorescent sensors, removing the limitation of single use sensors.