[Resonance light scattering of 4-(2-pyridylazo)-resorcinol (PAR)].

Mechanism and influence factors of resonance light scattering (RLS) spectra of 4-(2-pyridylazo)-resorcinol (PAR) aqueous solution were studied. In weak acidic solutions, strong RLS of PAR can be observed. The spectral feature of RLS is related to the absorption spectra of PAR. Acidity of the solutions influenced the acid-base equilibrium of PAR and its existing state, thereby influenced the RLS intensity. At pH 3.1 to pH 6.2, PAR exists as neutral molecule, which may assemble into molecular aggregates by hydrophobic force giving a light scattering enhancement. By a light polarization experiment, the RLS of PAR was demonstrated to be complete polarized light. The relationship between RLS intensity and PAR concentration was examined to be linear at a given set of experimental conditions.