AbstractThe absorption spectra and relative basicities ofp‐dimethylamino‐azobenzene and of ten of itsp′‐ orm′‐substituted derivatives have been determined. The bathochromic shift of the long‐wave π → π*‐transition on protonation of the azo link and the pK′1values for this particular acid‐base equilibrium have been compared with the respective values found previously for correspondingly substi