Nucleophilic aromatic substitution of 2,6-O-dimethyl-p-cyclodextrin (beta-DMCD)-complexed 4-fluoro-3-nitroaniline derivatives with poly(vinyl amine) (PVAm) in water results in 2-nitro-1,4-benzenediamine-functionalized water-soluble PVAms in one step. The 2-nitro-1,4-benzenediamine moiety linked to the polymer is solvatochromic and undergoes protonation and deprotonation as function of pH as shown by UV-Vis spectroscopy. The occurrence of an isosbestic point in the UV-Vis spectrum is suitable to directly determine the pK(a) value using the Henderson-Hasselbalch equation. The influence of the methyl group substitution of the polymer and the 2-nitro-1,4-benzenediamine moiety on the pK(a) is discussed.