PVC undergoes a high degree of dehydrochlorination when exposed to energetic photons. The released HCl (acid), however, can be trapped if a suitable trapping material (base) is also enclosed within the solid matrix as a result of formation an acid-base adduct. Color changes or electrical conductivity changes can easily be obtained if suitable acid-base indicators or conducting polymers in their basic (nonconducting) form are enclosed in the matrix as trapping materials. We used bromcresol green and polyaniline for inducing color and electrical conductivity changes, respectively, within the PVC matrix as a result of exposure to UV light at 254 nm. Both changes can to some extent be reversed by further exposure of the films to NH3 vapour. The color and electrical conductivity changes and their reversibility were followed by using UV–Vis, IR and XPS spectroscopic techniques. q