Sensoric properties of aromatic and heterocyclic compounds with conjugated bonds

Dipyridyldiketopyrrolopyrrole and phenylpyridyldiketopyrrolopyrrole were investigated in terms of the effect of acid vapour on their properties, in comparison with diphenyldiketopyrrolopyrrole. Materials were deposited by vacuum evaporation in the form of thin films ca. 100 nm thick. Reversible changes of UV-VIS absorption spectra as well as those of IR absorption spectra when treated with acid vapour were tested. The explanation for the protonation of the ternary nitrogen atom in the pyridyl ring was found. The conductivity measured in a gap electrode arrangement increased by 5 to 6 orders of magnitude. All changes remained stable, unless the sample was regenerated by annealing at 170 °C and the entire process was fully reversible. The compounds exhibit good thermal and chemical stability and are suitable as detector materials in sensors of acids, vapours, and hydrogen.