Optical response of 6FDA–DAD fluorinated polyimide to water and alcohols

Thin films of a fluorinated polyimide derived from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride and 2,3,5,6-tetramethyl-1,4-phenylenediamine have been obtained by spin-coating a solution of polyimide powder dissolved in chloroform. The synthesized polyimide has been characterized by Fourier transform infrared spectroscopy, optical transmission spectroscopy and fluorescence spectroscopy. Significant changes in some intrinsic fluorescence features such as the intensity, the shape and the position of the emission peaks have been observed under exposure to vapours of water, ethanol and isopropanol. These effects have been correlated to the developing of specific chemical interactions between these analytes and the macromolecules, including the formation of hydrogen bridges. In order to determine the detection capabilities and the response and recovery times towards the various analytes, single-wavelength fluorescence versus time measurements have been performed as the polyimide films were exposed to alternating pulses of pure nitrogen and different vapour concentrations. The polymer proved capable to respond to all the tested analytes, with response and recovery times in the order of the tens of seconds and detection thresholds in the 500–1000 ppm range.