Spectral investigation of conjugated azomethines: A large palette of colors possible with acid and oxidant doping

The color transitions between the neutral and doped states of a series of heterocyclic azomethines were investigated in both thin films immobilized on glass substrates and in solution. Their doping and subsequent dedoping of the intermediate could easily be followed spectroscopically owing to their strong visible absorbance. With all the azomethines, spectral changes occurred when doped with trifluoroacetic acid and ferric chloride. Absorbance bathochromic shifts up to 250 nm were observed and these were contingent on the azomethine structure. Meanwhile, the doping was found to be fully reversible with no detectable azomethine decomposition. Reversible color changes were also possible with Lewis acids. The shift in the absorbance spectrum was contingent on the Lewis acid.