Aggregation and tautomeric properties of CI Acid Red 138

Abstract The spectral properties of CI Acid Red 138 and related dyes in respect of their azo(A)-hydrazone(H) tautomeric behavior were investigated. The observed influence of temperature and concentration was taken into account in the described theoretical model. The absorption spectra of the H-form and its corresponding H-dimer were calculated along with the structural parameters—the distance R between the molecules in the dimer (∼5.3 A) and the angle α between the transition dipole moments (∼56°).